MACAO-VLTI First Light - ESO

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MACAO-VLTI First Light - ESO Powered By Docstoc
					                                                                                                    No. 112 – June 2003




Computer simulation of the Atacama Large Millimeter Array (ALMA). Image created by Herbert Zodet.

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     T E L E S C O P E S A N D I N S T R U M E N TAT I O N
Progress with the
Atacama Large Millimeter Array (ALMA)
CATHERINE CESARSKY, Director General of ESO
   The ALMA project has made remark-           construction of the VLT, was named              sembled at the site. These tests will be
able progress over the last several            Director of the ALMA Project in April.          critical in deciding on the 64 production
months, as important agreements have              The European ALMA Board (EAB)                antennas.
been signed, the project structure final-      was also established by ESO Council,               Work on the many other aspects of the
ized and prototype antennas moved              to oversee the European side of the             project continues at an accelerating pace,
from construction to testing.                  project, and the European Scientific            with several contracts being awarded or
   The most important milestone, of            Advisory Committee (ESAC) was ex-               in preparation. The work covers all as-
course, was the signing in February of         panded. Both have representation from           pects of the project, including system en-
the Bilateral Agreement between ESO            all ESO member states and Spain. An             gineering, the layout and development of
and the U.S. National Science Foun-            ALMA Division within ESO was formally           the site infrastructure, the antenna trans-
dation for the construction and opera-         established at the beginning of the year,       porters, the receivers and associated
tion of ALMA, as reported in the last is-      and key personnel continue to be hired.         hardware and electronics, the backend
sue of The Messenger. Following the               Negotiations with the Chilean govern-        subsystems, software development, cali-
signature of the agreement with Spain          ment have been proceeding rapidly and           bration, and many others.
for ALMA participation in January, this        successfully. In October 2002, an                  In parallel with all this activity, discus-
gave the final green light for the ALMA        agreement between Chile and ESO was             sions with Japan continue concerning
project. At the same time the ALMA             signed authorizing ESO to establish a           the possibility of its becoming a major
Board was formally established, to             new centre for astronomical observation         partner, with the enhancements that this
oversee the realization of the project via     in Chile – the ALMA Observatory on the          would bring to the project. A decision by
the management structure; P. van der           Plateau of Chajnantor, near San Pedro           the Japanese government may be
Kruit, President of ESO Council, is also       de Atacama. This agreement has been             made this year, for possible entry into
the first ALMA Board Chairman. The             ratified by the Chilean parliament.             the project early next year.
Board has since approved the Project              An important aspect in the develop-
Plan that had been under development           ment of ALMA is the manufacture and
through the Phase 1 period, and has es-        testing of two prototype antennas. The
tablished the Joint ALMA Office with           first prototype, produced by VertexRSI,
overall management responsibility un-          is under test at the ALMA Test Facility in
der the Board. Massimo Tarenghi, who           New Mexico, and the second prototype,
played such an important role in the           produced by Alcatel/EIE, is being as-




On 16 May 2003, at the airport of Milano Malpensa, the receiver cabin and reflector backup
structure (BUS) of the Alcatel/EIE Antenna prototype were loaded on the special Airbus A 300
transporter (“Beluga”) for shipment to Albuquerque airport (NM, USA) en route to their final
destination, the VLA site in Socorro. Both cabin and BUS were manufactered in Italy and are
made of carbon fibre reinforced plastic (CFRP) based on a design by the European Industrial    Computer simulation illustrating the “zoom
Engineering (I) under the supervision of Alcatel Space Industries (F).                         array” of ALMA.


2
The Science Verification of FLAMES
FRANCESCA PRIMAS, User Support Group, ESO
   After a new VLT instrument has been         sition of UVES and GIRAFFE observa-         munity at large) and the proposed ex-
commissioned and thoroughly tested1, a         tions.                                      ploitation of the instrument capabilities:
series of scientific and technical check-         The FLAMES Dry Runs took place
ups are scheduled in order to test the         successfully between the end of             • The Chemical Signature of Different
front-to-end operations chain before the       January and the beginning of February       Stellar Populations in the LMC: al-
official start of regular operations.          (Jan 24 – Feb 03, 2003). Nine science       though it is considered an intermediate-
Technically speaking, these are the so-        programmes, proposed and assembled          age galaxy, the LMC is characterised by
called Dry Runs, part of which are usu-        by the FLAMES SV Team (which in-            a large range of stellar ages, from a
ally devoted to the Science Verification       cluded the VLT Programme Scientist,         genuine old to a prominent young pop-
(SV for short) of that specific instru-        the Instrument PI, the Paranal              ulation. The main goal of this project
ment.                                          Instrument Scientist, the User Support      was to investigate further its metal en-
   A Science Verification programme in-        Astronomer, members of the FLAMES           richment history by measuring the
cludes a set of typical scientific obser-      Commissioning and Science Advisory          abundances of several elements for a
vations with the aim of verifying and          Teams and representatives of the            statistically significant sample of Red
demonstrating to the community the ca-         FLAMES Consortia), were executed.           Giant Branch stars (17 < Vmag < 18).
pabilities of a new instrument in the op-      More than 5200 spectra were collected       Two complementary projects were com-
erational framework of the VLT Paranal         during the ten observing nights, and        bined: (1) the first spectroscopic metal-
Observatory. Though manifold, its goals        publicly released on March 3, exactly       licity determination of the LMC Clump to
can be summarised in two main points:          one month after the last observing          verify its influence (if any) on the intrin-
from the scientific point of view, by          night. This one-month time lag was nec-     sic luminosity of the stars (by allocating
demonstrating the scientific potential of      essary to visually inspect the quality of   1/4 of the Medusa fibres to Clump
the new instrument, these observations         the frames (both raw and reduced), to       stars); (2) the chemical analysis of LMC
will provide ESO users with first sci-         make the correct association between        Long Period Variables in order to inves-
ence-grade data, thus fostering an ear-        raw and calibration frames to be distrib-   tigate the connection (if any) among
ly scientific return. From the technical       uted, and to prepare a detailed set of      their chemical composition, pulsation
point of view, by testing the whole oper-      summaries and technical explanations.       mode, and evolutionary phase (the
ational system (from the preparation of        Any user from one of the ESO Member         UVES fibres were used for this pur-
the observations to their execution and        States and with an active registration      pose). Figure 1 shows the H-α region
analysis), it will provide important feed-     to the ESO/ST-ECF Archive (see              for one RGB, one Clump, and one LPV
back to the Instrument Operation               http://archive.eso.org/register/new for     star.
Teams (both in Paranal and in                  more information), can download the
Garching), to the Instrument Division,         FLAMES SV datasets, whose scientific        • Massive Kinematic Study of
and to the Data Flow groups. More de-          justifications are briefly described be-    NGC 5128 using its Planetary
tails about the concept(s) behind a            low. The interested reader is reminded      Nebulae and Globular Clusters as
Science Verification can be found in the       that a wealth of details (such as colour-   Test Probes: planetary nebulae (PN)
“Science Verification Policy and               magnitude diagrams - to check which         are emission line objects, the systemic
Procedures” document (available at             targets were observed, Field Charts         velocities of which can be probed using
http://www.eso.org/science/vltsv/).            and README files - two of the main          the brightest emission lines (see
                                               user requirements) are available            Figure 2). The 785 PN found and cata-
Science Goals and Achievements                 from the FLAMES SV web page                 logued by Hui et al. (1993), over a large
                                               (http://www.eso.org/science/vltsv). The     area (40 46 arcmin, EWxNS) of
   The Fibre Large Array Multi-Element         following SV programmes were select-        NGC 5128 (Centaurus A) were targeted
Spectrograph (FLAMES) is the new               ed based on their scientific weight (they   in order to verify the initial findings that
multi-object, intermediate- and high-          must be interesting for the ESO com-        PN kinematics trace a triaxial potential,
resolution spectrograph of the VLT
(Pasquini et al. 2002). Mounted at the
Nasmyth A platform of Kueyen (Unit
Telescope #2), FLAMES can access
targets over a large corrected field of
view (25 arcmin diameter). It consists of
three main components: a Fibre
Positioner (OzPoz) hosting two plates
(while one plate is observing, the other
is positioning the fibres for the next ob-
servation); a link to the Red Arm of
UVES (the high-resolution Ultraviolet
and Visible Echelle Spectrograph) via 8
single fibres of 1 arcsec entrance aper-                                                                           Figure 1: The H-α
ture; a medium-high resolution optical                                                                             region as observed
spectrograph, GIRAFFE, equipped with                                                                               with Medusa and
three types of feeding fibre systems:                                                                              UVES (top spec-
130 MEDUSA fibres, 15 deployable in-                                                                               trum) in three stars
tegral field units (IFU), and 1 large, fixed                                                                       representative of
integral field unit (ARGUS). A special                                                                             the different stellar
Observing Software (OS) coordinates                                                                                populations probed
the operation of the different subsys-                                                                             in the Large
tems, also allowing simultaneous acqui-                                                                            Magellanic Cloud.
1
 Please note that all commissioning data are now available from
http://www.eso.org/science/flames_comm/                                                                                               3
Figure 2: H-β and two [O III] lines in emission (the 495.9 and
500.7 nm), as detected in one of the planetary nebula observed
with one Medusa fibre, at low resolution. More than 500 PN were
observed in total.
                                                                  Figure 3: Two mass-loss diagnostics: the Ca H,K and the NaD lines, as
                                                                  observed in two different RGB stars of NGC 2808.

with the mass-to-light ratio increasing       •Elemental Abundances in NGC 2243:              • Probing Activity and Angular Mo-
with radius (thus suggesting the pres-        a complete chemical analysis of sub-gi-         mentum Evolution of Low-Mass
ence of a dark matter halo). Some             ant stars and membership information            Members of the Orion Nebular
MEDUSA and all UVES fibres were al-           for the fainter, turn-off stars in this open,   Cluster: surface rotation is a key ob-
located to the brightest globular clusters    metal-poor, intermediate-age (~ 2 Gyr)          servational parameter for stellar evolu-
of this giant elliptical galaxy in order to   cluster were the main goals of the pro-         tion, being tightly linked to the internal
compare their kinematics and to derive        gramme, which used two contiguous               angular momentum transport, hence to
their metallicity.                            (hence slightly overlapping) high-reso-         mass loss. The main goal of this pro-
                                              lution Medusa set-ups (Figure 4). The           gramme was to determine the v sini dis-
• Mass Loss in Red Giant Stars of             main scientific interest of this cluster lies   tribution for a large number (120 tar-
the Globular Cluster NGC 2808:                in two aspects: its metallicity, which is       gets, selected from the low-resolution
about 100 stars of the Red Giant              comparable to the halo cluster 47               survey of Hillenbrand 1997) of low-
Branch, in the magnitude interval             Tucanae, and its age which is instead           mass (0.2–0.06 M ), relatively cold
V=13.2–16.5 mag, within a radius of           remarkably smaller (47 Tuc formed               (logTeff < 3.5), M5–M7 type stars in the
about 7 arcmin from the cluster centre,       some 10–12 Gyrs earlier). A direct              Orion Nebular Cluster (~1 Myr old,
were targeted, with the aim of measur-        abundance comparison between these              430 pc away), for which only little infor-
ing shifts of the CaII-K3, NaD and H-α        two clusters (47 Tucanae has been ex-           mation is available. Recent observa-
core line profiles that are major diag-       tensively observed with UVES in the             tions in Orion have shown that while the
nostics of mass outflow, hence mass           past) will shed light not only on their         majority of low-mass pre-main se-
loss. In order to observe the Ca H and        chemical history, but also on the forma-        quence stars are rotating at rates ap-
K lines, this programme made use of           tion and evolution of our own Galaxy.           proaching 30% of breakup, late-type
one of the bluest settings available on
FLAMES, HR#2, which covers the
spectral range between 385 and
405 nm (see Figure 3). The brightest
stars of the cluster were observed si-
multaneously with UVES, to obtain a
larger spectral coverage (480–680 nm)
for chemical abundance purposes.

• Geometric Distances of the Galactic
Globular Cluster NGC 2808: the main
idea behind this science case was to
observe a very large number of stars
(1000), and derive their radial velocities,
in order to obtain the first determination
of the cluster geometric distance (with
an uncertainty of 2–3%, i.e. an age with
an error less than 1 Gyr) via a direct
comparison of the radial velocities to
the (already available) proper motions.
One GIRAFFE set-up (HR#5), together
with the simultaneous allocation of
UVES-fibres, was also used to obtain
spectra of horizontal branch stars, thus
increasing by one order of magnitude
the size of the present sample.               Figure 4: The same NGC 2243 sub-giant star, as observed in two contiguous high resolu-
                                              tion Medusa settings: the total spectral coverage is from 638 to 697 nm.


4
stars in older clusters appear to be slow     Figure 5: The efficiency
rotators (e.g. Stassun et al. 1999, and       rate achieved during the
Queloz et al. 1998, respectively).            FLAMES Dry Runs:
                                              “Science” means the
• Kinematics of Distant Galaxies from         time spent on target, with
FLAMES-GIRAFFE IFU Mode: the                  respect to the “astronom-
main goals of this programme were a)          ical” length of each night,
to derive, from spatially-resolved spec-      whereas the values on
troscopy and HST images, velocity             the “Science+Acquisition”
fields and rotation curves of galaxies        curve also include the
with emission lines at moderately high        time spent on acquiring
redshift; b) to kinematically map merg-       the target fields and the
ing systems, in order to quantify the         set-up of the instrument.
number of perturbed galaxies and the
merging rate; c) to study the evolution of
the Tully-Fisher relation in order to com-    persion and infer some constraint on         ticular phase during which a user, with
plement the study of the mass and M/L         the ellipsoid of velocity dispersions in     advice (if needed) from a pre-assigned
functions. The chosen target was the          the central part of the galaxy NGC 3585.     support astronomer, submits a set of
well-known cluster of galaxies, MS            This programme made use of one high-         Observation Blocks (i.e. logical units of
1054-03, at redshift z = 0.83. FLAMES         and one low-resolution setting (HR#12        exposures to be executed at the tele-
was used in combined mode: the 15             and LR#05, respectively) using the           scope to obtain a coherent set of data)
Integral Field Units were mainly allocat-     same fibre configuration.                    and detailed information on how her/his
ed to late-type galaxies Sc-Sd, merger                                                     own programme should be carried out.
systems and post-starburst spiral galax-        The time spent on each of these pro-       This process requires the availability of
ies, whereas UVES fibres were devoted         grammes and their completion rate (giv-      software tools, documentation, and a
to four elliptical galaxies and one merg-     en in percentage), together with the         list of generic and instrument-depend-
ing system, all brighter than 21 mag in       chosen instrument modes and set-ups,         ent requirements that need to be ful-
I-band.                                       are summarised in Table 1.                   filled.
                                                                                               In the case of a SV Phase 2, this
• Dark and Stellar Mass in Late-type          A Success                                    process must be anomalous, by defini-
Dwarfs: even if the existence of dark                                                      tion: the instrument has not yet been re-
matter in spiral galaxies is well estab-         Three important factors are behind        leased for official operations, and all
lished, there are large uncertainties re-     the success of the FLAMES SV : a sta-        software tools, user documentation and
garding its distribution inside the optical   ble instrument, very cooperative atmos-      user manuals are still in the final stages
disc. The aim of this programme was to        pheric conditions, and a set of well pre-    of revision. These uncertainties clearly
measure the (stellar) vertical velocity       pared science observations. The com-         require some flexibility on the side of the
dispersion, from which one can directly       bination of the first two points made it     SV Team while preparing the observa-
measure the product M/L × q0, where           possible to achieve a very high efficien-    tions (this is also why a SV Team main-
M/L is the stellar mass-to-light ratio of     cy over the entire window of the ob-         ly includes people who have been al-
the stars and q0 the thickness of the         serving run, as shown in Figure 5,           ready exposed to the instrument, during
disc. Observationally, this requires high     where the time spent on “science tar-        its development, assembling, and com-
spectral resolution: the selected target,     gets” and normalised to the total num-       missioning phases).
NGC 1310, is less massive than the            ber of hours available per night (as de-         In the case of FLAMES SV, Phase 2
Milky Way; it rotates at 110 km/s, thus       fined by the astronomical twilights) is      took place over the Christmas break. All
requiring a velocity resolution of the or-    shown for the entire run. On the third       the required material was delivered to
der of 10–20 km/s. The target was se-         aspect, i.e. the preparation of the sci-     ESO in mid January, then checked and
lected to fulfil the following criteria:      ence observations, a more extensive          verified by the FLAMES user support
preferably late-type, close to face-on,       and detailed description is needed.          astronomer, and made available to the
and not barred. The observations were            In the very early organisational phas-    team of night- and day-time astro-
carried out with 5 IFU placed at a radius     es of the FLAMES SV, it was decided to       nomers present on Paranal for the exe-
of 1 scale length and the remaining 10        try and implement a real (although for       cution of the observations. During this
at a radius of 2 scale lengths.               many aspects anomalous) Phase 2.             phase, a thorough assessment of the
                                              With this term, familiar to all those as-    quality of the available tools and manu-
• Dynamical Study of Elliptical               tronomers who have had their observa-        als was made, which proved to be very
Galaxies: the scientific objective was        tions carried out in “Service Mode” (cf      useful for the official Period 71 Phase 2,
to accurately determine the velocity dis-     Silva 2001), we usually identify that par-   that started at the beginning of February

Table 1: FLAMES SV Science Programmes
Programme                                Instr. Mode           Instr. Set-Up             Invested Time    Completion Rate
                                                                                             hours            %

NGC 5128: PN and GC                     Medusa+UVES         LR3+R580                          7                  75
LMC: Stellar Populations                Medusa+UVES         HR13,14+R580,R860                21                  76
NGC 2808: Mass loss                     Medusa+UVES         HR2,11,14+R520                    4                 100
NGC 2808: Geometric Distance            Medusa+UVES         HR5,9+R520                        7                 100
NGC 2243: Abundances                    Medusa+UVES         HR14,15+R580,R860                 4                 100
ONC: Low-mass Stars                     Medusa              HR14,15                           5                  62
MS 1054-03: Kinematics                  IFU+UVES            LR6+R860                          9                  75
NGC 1310: Dark and Stellar Mass         IFU                 LR4                               5.5               100
NGC 3585: Dynamics                      IFU                 HR12,LR5                          5                 100



                                                                                                                                    5
                                                packages to the users), and the               der to have a quick-look at the spectra
                                                Instrument Division in Garching (which        quality, while observing. All these
                                                has been responsible for developing,          “quick-look” reduced spectra were pub-
                                                building and commissioning the instru-        licly distributed together with the raw
                                                ment).                                        science and calibration frames, so that
                                                   The FLAMES SV has been a very              the entire ESO community could bene-
                                                positive experience, also from the oper-      fit equally from this set of observations.
                                                ational point of view. The lessons            Those observations for which no quick-
                                                learned during the implementation, exe-       look spectrum could be extracted, were
                                                cution, and quality assessment of these       promptly made available to the Data
                                                FLAMES observations have proven to            Flow System group, in order to test the
                                                be very valuable, for the instrument          robustness and repeatability of the
                                                support teams and also for the first          pipeline-reduction framework against
                                                FLAMES users (i.e. those with FLAMES          different sets of science data.
                                                programmes approved for P71), who
                                                benefited from more robust and user-          The End of the Adventure
                                                friendly instrument-related tools.
                                                   The first positive outcome came from          In retrospect, as the FLAMES SV co-
                                                the (SV) Phase 2 exercise, which              ordinator, I must say that the very posi-
Figure 6: The centring of the reference stars   turned out to be a thorough testing of        tive and successful experience of the
on the Fibre Acquisition Coherence Bundles,     the FLAMES Fibre Positioner Obser-            FLAMES Science Verification Dry Runs
as seen at the telescope console.               vation Support Software (FPOSS) on            has undoubtedly resulted from the hard
                                                real and different science cases (for         work of several people, who deserve to
(see next section). Passing the Phase 2         which the user wants to allocate one          be properly acknowledged. First of all,
verification usually offers the user and        specific group of fibres to one specific      the FLAMES SV Team members (led by
the operations team some confidence             group of targets). This revealed a series     A. Renzini, and including M. R. Cioni, N.
that the execution of a given pro-              of shortcomings in the FPOSS tool,            Cretton, A. Kaufer, C. Melo, L. Pasquini,
gramme should go smoothly. However,             which was revised and further tested as       M. Rejkuba, M. Romaniello J. Walsh, M.
should the user have mistyped some              SV observations were taking place.            Zoccali, and myself - at ESO - and A.
crucial information (like the target coor-      Among the technical problems encoun-          Blecha, C. Cacciari, V. Cayatte, and V.
dinates), this will be detected only at the     tered at the telescope, the most recur-       Hill, as representatives of the FLAMES
telescope. Because of the multiplex ca-         ring one was the “non-validity” of some       Consortia) for having proposed and de-
pability of FLAMES, target coordinates          UVES+Medusa fibre configurations,             veloped the science cases in a very
are even more important for successful          which had instead been validated by           flexible and timely manner. The Paranal
observations. One needs very precise            FPOSS during Phase 2. The need for            FLAMES SV Team (A. Kaufer, J.
relative coordinates of several hun-            solving this type of problem in real-time     Smoker, R. Schmutzer, C. Melo, M.
dreds of targets in the field to be ob-         gave us a deeper understanding of how         Rejkuba and myself) played a funda-
served - technically speaking, one              fibre-collisions were handled and treat-      mental role in securing an excellent set
needs very accurate astrometry (< 0.3           ed, both at FPOSS and OzPoz levels. A         of first-grade science data (considering
arcsec). As FLAMES does not have a              quick recovery procedure at night time        all the debugging, fixes and revisions
pre-imaging option, there is only one           (by “manually” de-allocating the collid-      implemented in real time at the tele-
parameter/tool available to evaluate the        ing fibres) was then followed by the de-      scope). One of the main strengths of
quality of the astrometry: Figure 6             bugging phase at software level during        this group was its very positive, friendly,
shows an image of the Field Acquisition         day-time operations, perfectly in time to     and constructive team spirit. Among the
Coherence Bundles (as seen at the tel-          test the newly revised version during         ESO Fellows, the extra workloads un-
escope console) for one set of observa-         the following night.                          dertaken at different stages of the
tions that were carried out during the             As SV observations are carried out in      FLAMES SV adventure by M. Rejkuba,
FLAMES SV. These bundles (normally              Service Mode, the presence or absence         M. Zoccali, and N. Cretton need to be
four, but at the time of the SV run the         of difficulties during the execution of a     recognised. Finally, the cooperation of-
fourth one was not available) show how          given programme (based on the infor-          fered by the ESO/ST-ECF Science
well centred the reference stars are,           mation provided by the Principal              Archive (in particular, B. Pirenne and N.
which must be chosen in the same as-            Investigator) gave us an idea of how          Rainer) made it possible to release all
trometric solution as the science tar-          complete the preliminary list of user re-     the data packages on a very com-
gets.                                           quirements (set up during the SV Phase        pressed timescale. Thank you all!
                                                2) was. Because of the presence at the
Lessons Learned                                 telescope of most of the persons in-          Acknowledgements
                                                volved in the FLAMES operations, it
   As stated at the very beginning of this      was possible to revise in real time all the     The author would like to thank
presentation, one of the main goals of a        user-related documentation (e.g. User         Pamela Bristow for a careful reading of
Science Verification run is the important       Manuals) and the software tools, like         the manuscript.
technical feedback that can be given to         FPOSS, thus solving and implementing
the teams directly involved in the front-       all the “bugs and wishes” we had as-          References
to-end operations of that instrument, i.e.      sembled after Phase 2, and to prepare
the Paranal Science Operation team              all FLAMES operations-related Web             Hillenbrand, L. A., 1997, AJ, 113, 173
(responsible for its operations), the           pages.                                        Hui, X., Ford, H. C., Ciardullo, R., Jacoby, G.
User Support Group (the operational-in-            As the observations were being car-           H., 1993, ApJS, 88, 423
terface between the users community             ried out, we also tried to reduce all the     Pasquini, L. et al., 2002, The Messenger,
and the Observatory), the Data Flow             frames in a semi-automatic way, with             110, 1-9
groups (i.e. those behind the develop-                                                        Queloz, D., Allain, S., Mermilliod, J.-C.,
                                                the reduction recipes available at that
                                                                                                 Bouvier, J., Mayor, M., 1998, A&A, 335,
ment of instrument-specific data-reduc-         time. This was done on a best-effort ba-         183
tion recipes, the implementation of qual-       sis, as it was a low priority item on the     Silva, D., 2001, The Messenger, 105, 18-24
ity-control and monitoring checks, the          FLAMES SV team “to-do” list. However,         Stassun, K. G., Mathieu, R. D., Mazeh, T.,
archival and distribution of the data-          it was decided to invest the effort in or-       Vrba, F. J., 1999, AJ, 117, 2941

6
MACAO-VLTI First Light: Adaptive Optics at the
Service of Interferometry
R. ARSENAULT 1, J. ALONSO 2,H. BONNET 1,J. BRYNNEL1, B. DELABRE1, R. DONALDSON 1,
C. DUPUY 1 , E. FEDRIGO1, J. SPYROMILIO 3,T. ERM 3,J. FARINATO 4 , N. HUBIN 1 , L. IVANESCU 1,
M. KASPER1, S. OBERTI1, J. PAUFIQUE1, S. ROSSI1, S. TORDO1, S. STROEBELE1, J.-L. LIZON1,
P. GIGAN 4,F. POUPLARD5, F. DELPLANCKE1, A. SILBER1, M. QUATTRI1, R. REISS1
1
 European Southern Observatory, Garching, Germany; 2ESO, La Silla, Chile; 3ESO, Paranal, Chile;
4
 Astronomical Observatory of Padova, Italy; 5LESIA, Observatoire de Paris, France

   The Multiple Application Curvature
Adaptive Optics (MACAO) programme
was initiated by ESO in 1998 to fulfil the
high angular resolution requirements of
the VLT Interferometer (Glindemann et
al., 2002) and also instruments like SIN-
FONI (Bonnet et al., 2002) and CRIRES
(Moorwood et al., 2002). After a learn-
ing phase of two years with the labora-
tory Curvature prototype delivered by
Laplacian Optics, the ESO Adaptive
Optics Department set up a project
team at the beginning of 2000 for the
line production of seven MACAO sys-
tems (Donaldson et al., 2000): four for
VLTI, one for SINFONI, one for CRIRES
and one spare. Although the AO key
components are similar for these seven
systems, the opto-mechanical imple-
mentations are different for the VLTI,
SINFONI and CRIRES. In the following
we will concentrate on the VLTI imple-
mentation.
   The main aim of MACAO-VLTI is to
feed the VLTI with a corrected wave-          Figure 1: The location of the Coudé focus where the MACAO-VLTI systems are installed.
front, to improve light injection efficien-   MACAO is the black box under the M9 tower (arch) shown on the photograph.
cy in the monomode fibres. The existing
Coudé mirror train M8 is replaced by the
corrective optics. The MACAO-VLTI
Wave Front Sensor (WFS) is located
just below M9 on the Coudé platform
(Figure 1). M9 is a dichroic that allows
the wavefront sensing in the visible
(transmits 0.45–0.9 µm) and reflects the
wavelengths 1 to 13 µm to the recombi-
nation laboratory.
   Simulations done for the design re-
views show that MACAO-VLTI will
reach a Strehl ratio of 0.58 at 2.2 µm on
bright stars (V < 10) with a seeing of
0.65 and this has been confirmed by
tests in the laboratory. Limiting magni-
tude is evaluated at V ~ 18 which would
result in a Strehl ratio slightly under
~0.1. MACAO will also operate with
worse seeing (1.0 ) but the correction is
less spectacular (expected Strehl ratio
of 0.39).
   The first MACAO-VLTI system was
delivered to Paranal on UT2 in April
2003, and results from the first light are
                                              Figure 2: MACAO exploded view. The T-Mount, at the centre, is the main structure holding
shown further down in this article. The
                                              all components. On the front side one can see the shutter and BSD (top), the WFS optics
other three systems will follow at 6          (just below) and STRAP with its density filters wheel (at the lower-left). The TCCD (centre-
month intervals. By the end of 2003 the       bottom) and the membrane mirror on its gimball mount (lower-right) complete the equipment
first two systems will be available and       mounted on the front side of the T-Mount. On the back side are installed the last elements in
will allow wavefront corrected beam re-       the optical path namely: the density filter wheel, the rotating unit and the derotator prism and
combination at the VLTI.                      finally the micro-lens mount (upper right).


                                                                                                                                            7
Figure 3: Opto-                                                                                varying number of lenslets: 4, 8, 12, 16
Mechanical setup                                                                               and 20. The Fibre Optic Bundle is made
of MACAO-VLTI                                                                                  of the lenslets and 60 optical fibres ter-
on the XY table                                                                                minated by FC connectors. It brings the
in the Coudé                                                                                   light to the 60 APD WFS Detectors.
room during
installation. The                                                                              Corrective optics
BSD can be seen                                                                                    The Deformable Mirror is fabricated
in the uppermost                                                                               by CILAS (France) and is of the bi-
part; the very                                                                                 morph type. Five such mirrors have
crowded area on                                                                                been ordered (four units plus one
the left-hand side                                                                             spare) and a prototype for development
hosts the WFS                                                                                  and tests. The surface quality with volt-
optics and the                                                                                 age applied can reach 10 nm RMS.
membrane mirror                                                                                Less than 60 Volts are required to flat-
gimball mount.                                                                                 ten the DM which leaves ample reserve
Water pipes can                                                                                for seeing correction (range of –400 to
be seen on the                                                                                 +400 V can be applied). The reflectivity
right side and are                                                                             is on average 99% in the IR (λ > 1 µm)
used for the cool-                                                                             and larger than 97% in the visible. It has
ing of the TCCD and STRAP units (if not helping in recognizing the components, this            been dimensioned to provide AO cor-
picture has at least the benefit of showing the complexity of the setup !).                    rection for seeing values up to 1 .
                                                                                                   The Tip-Tilt Mount is a custom design
                                                                                               from the Observatoire de Paris (LESIA).
MACAO-VLTI design                             ed in the pupil plane for curvature analy-       It is based on a gimball mount in which
                                              sis. The WaveFront Sensor Optics, a              the DM is inserted. The assembly is
Opto-mechanical design                        set of four diamond turned mirrors in a          controlled by a dedicated electronics
   The existing Coudé mirror train feeds      single mount, can be changed as a unit.          with its own internal 1 kHz control loop
the delay lines of the VLTI before beam       A Derotator Prism is needed to com-              which makes tests and integration trou-
recombination; this constitutes the “sci-     pensate the rotation between the DM              ble-free. The bandwidth of the system
ence path” of the system. M8, which co-       (rotates with azimuthal axis) and the            has been tuned at 100 Hz for both axis
incides with a pupil plane, is replaced by    lenslet array (at rest on the Coudé plat-        and the stroke is 240 arcsec PV me-
a 60 element bimorph mirror coupled           form). Figure 4 depicts the lenslet array        chanical which corresponds to 6 arcsec
with a curvature Wavefront Sensor             unit which consists of two arrays with 60        on the sky.
(WFS). The WFS detectors are 60               subapertures each and 60 optical fi-                 Figure 5 shows the bimorph DM in-
Avalanche Photo-Diodes (APDs) from            bres. The purpose of this assembly is            serted into the Tip-Tilt mount. It also
Perkin-Elmer (Canada).                        essentially to gather the light in the indi-     shows how this assembly replaces the
   The whole MACAO-VLTI assembly              vidual sub-apertures and inject it into          conventional glass M8 mirror of the
sits on the Coudé platform under a            the corresponding optical fibres. The            Coudé train.
structure called the “M9 tower”. Figure 2     telescope pupil image is divided in 60               An important property of this is the
shows an exploded view of all MACAO           sub-apertures, distributed in 5 rings of         coincidence of the centre of gravity of
components. The whole assembly is
contained in a 650         770    850 mm
volume (including the XY table, not
shown in this view). MACAO-VLTI pro-
vides acquisition mode with TCCD plus
two main observing modes:
   • Adaptive Optics image correction
     (curvature 60-element)
   • Tip-Tilt correction (STRAP-M2 loop)
     on faint stars
   The so-called “XY Table”, based on
an ESO design, fulfils the field selector
function of the AO system. It positions
the MACAO assembly in the 240 mm (2
arcmin) field of view of the Coudé focus.
It has been proven to provide a 2 µm
relative positioning accuracy. All axis
motions are linear to better than 20 arc-
sec (pitch, roll and yaw). Figure 3 shows
a picture of the inside (front) of the
MACAO-VLTI “box”. The XY table can
be seen under the opto-mechanical as-
sembly. Despite the small volume, one
can see that space is scarce and inte-
gration/alignment definitely requires
some skill.
   The WFS box is composed of the fol-
lowing components. The Membrane
Mirror, an aluminised pellicle mounted        Figure 4: MACAO Lenslet array unit: The MACAO lenslet array unit is an original design and
on a loudspeaker to be set in vibration       production of ESO. It uses two lenslet arrays in cascade. The first curvature lenslet array dis-
at 2.1 kHz. It is located in the image        sects the telescope pupil and focuses the light on the second ball lenslet array which concen-
plane and produces the defocus need-          trates and injects the light into the optical fibres connected at the other end to the 60 APDs.


8
the DM and its supporting ring with the          Electronics                                      ered by a wooden-insulated “coffin”-
intersection of the X and Y tilt axis. This         The MACAO-VLTI electronics is com-            type enclosure that reduces to a mini-
insures a better close-loop performance          posed of 4 cabinets containing all the           mum heat radiation in the Coudé room
of the TTM. Furthermore, the surface of          required electronics. Three of them are          and acoustic noise. Each cabinet’s heat
the DM is made coincident with the tilt          installed in the Coudé room: the RTC-            exchanger is connected to the SCP
axis (at centre) in order to have no opti-       VLTI cabinets, the IC cabinet and the            (Service Connection Point) which pro-
cal path difference produced when tilts          APD cabinet. The fourth one is located           vides the cooling fluid. No fans have
are applied.                                     on the VLT azimuth platform for its prox-        been implemented for the APD cabinet
                                                 imity to the corrective optics. All elec-        and all 60 APDs are mounted on cool-
Software                                         tronics conforms to the ESO standard.            ing “plates” in which the cooling fluid
   MACAO-VLTI is considered a tele-                 For the RTC hardware, an effort was           circulates. The azimuth platform cabinet
scope system and therefore is relative-          made to select commercially available            contains the DM voltage amplifier and
ly transparent to the astronomer. In the         component to insure a smooth integra-            the TTM servo-unit plus the usual cool-
end, the AO loop will be closed as part          tion into the VLT environment. Two               ing fans and heat exchanger.
of the interferometric source acquisition        PowerPC 2604 (400 MHz) boards are                   The HV amplifier has been designed
procedure. The so-called VLT-ISS (VLT            used, one as LCU controller (controls            and built by 4D Engineering (Germany)
Interferometer Supervisor Software)              VME rack and communication with out-             and uses a VME architecture. This rack
sends command to the MACAO-VLTI                  side world) and the second totally dedi-         is controlled by a PowerPC CPU and
OS (Observing Software) which coordi-            cated to the RTC calculation. A custom           signals are sent via a fast optical fibre
nates the operations of the MACAO                made APD Counter board (Shaktiware,              communication link. The rack contains
RTC (Real-Time Computer), ICS                    Marseille, France) is used to acquire the        4 boards which provide each 16 HV
(Instrument Control Software), STRAP             flux from the APD.                               channels for a total of 64. It is upgrade-
and TCCD subsystems.                                The membrane mirror is set in vibra-          able up to 15 boards (240 channels).
   In addition the MACAO OS supports             tion at 2.1 kHz; this function is managed        The 10 V signals to be sent to the TTM
the following observing modes:                   by the APD counter board, a solution             servo-unit also transit through the fast
   • Staring: a single acquisition in            chosen because a single board man-               optical fibre link.
which the AO loop remains closed dur-            ages the counter read rate and mem-
ing the entire observation.                      brane driving signal which need to be            Close loop & curvature
   • Chopping: an observation in which           well synchronized. The counts from the
M2 is used to shift the field from object        APD’s (intra-focal and extra-focal) tran-           A curvature system was chosen be-
to sky and back again. The AO loop is            sit on the VME bus and are acquired by           cause it offers a good performance for
synchronized (using the TIM board)               the RTC. They are processed (contrast            relatively low degrees of freedom, al-
with the frequency of M2 and the loop is         calculation and multiplication by control        lowing lower costs for components (DM,
opened during the chop on sky cycles.            matrix) and commands to the corrective           RTC, lenslet, etc. (Roddier, 1988)). It
   • Nodding: an observation in which            optics are sent at a frequency of 350            uses the curvature principle which is
the telescope is used to shift from object       Hz, hence 6 membrane mirror cycles.              that wavefront analysis is performed by
to sky and back again. The ISS informs           The time delay of the calculation has            measuring the intensity in 60 different
the MACAO OS of the nod to sky and               been measured to 310 µsec.                       sections of the pupil (sub-apertures).
nod to object cycles, the AO loop is                The VLTI LCU controls the STRAP               Measurements are performed with the
opened during the nod to sky cycles.             and TCCD operation for MACAO-VLTI                pupil defocused – so-called intra or ex-
   An engineering interface of the OS            while the IC cabinet (Instrument                 tra-focal images. This is produced by
has been designed and allows full con-           Control) contains a VME rack control-            the vibrating membrane set in vibration
trol of the functions during integration         ling all motorized functions. The two            at 2.1 kHz and the flux is then sampled
and tests.                                       cabinets are identical in size and cov-          at twice this frequency. The contrast
                                                                                                  value, (Iin–Iout)/(Iin+Iout), is proportional
                                                                                                  to the Laplacian, hence the curvature of
                                                                                                  the wavefront.

                                                                                                  Close loop control
                                                                                                     The commands are applied to the
                                                                                                  corrective optics at a frequency of 350
                                                                                                  Hz. The APD counter board provides
                                                                                                  the RTC with one set of intra/extra-focal
                                                                                                  counts every 0.48 msec. These counts
                                                                                                  are integrated by the RTC for 6 cycles
                                                                                                  and then multiplied by the command
                                                                                                  matrix to produce a command vector to
                                                                                                  be sent to the corrective optics. Besides
                                                                                                  acquiring WFS data, processing and
                                                                                                  sending commands to the correction
                                                                                                  optics (CO), the RTC also produces on-
                                                                                                  line diagnostic information and controls,
                                                                                                  a few electro-mechanisms (membrane
                                                                                                  mirror, neutral density filter and di-
                                                                                                  aphragm). Systematic aberrations sent
                                                                                                  to the CO can be off-loaded to the
                                                                                                  Telescope Control System (tilt & focus
                                                                                                  at 0.2 Hz).
Figure 5: Bimorph deformable mirror in its tip-tilt mount. On the left one can see the protect-      A watchdog is implemented to aver-
ed silver coating 100 mm in diameter. The bimorph mirror is held by a spring loaded radial 3      age the number of APD counts over a
points support in a dural ring. The assembly is inserted in the Tip-Tilt Mount (TTM) which can    tunable number of cycles to determine
tilt the DM during close loop. To the right is a picture of the DM mounted at the M8 location     whether they are over-illuminated.
of the VLT Coudé train. The hole on the left side leads up to M6.                                 There are two safety levels aiming at

                                                                                                                                             9
protecting the APDs from an over-illu-
mination. The routine which sends com-
mands to the DM is also responsible for
monitoring the voltages sent to the elec-
trodes. It clips values in excess of + or
–400 Volts, the maximum voltage.
   There is provision for a modal optimi-
sation, in which sensor data can be pro-




                                                 Strehl ratio
jected in another space where variable
gains can be used for the different
modes. Circular buffers can be generat-
ed to post-process sensor signals or
mirror commands off-line.

Piston free AO system
   For imaging purpose the piston pro-
duced by the deformable mirror in an
AO system is not critical and the main
concern is usually to avoid an accumu-
lation of piston applied on the DM which
would cause saturation of the elec-
trodes. One of the main challenges of                                              V magnitude
MACAO-VLTI is to insure that the cor-          Figure 6: The blue curve shows the simulated Strehl ratio versus guide star V magnitude. The
rective optics on 2 different UT’s do not      red curve shows the measured Strehl ratio in the laboratory (in K-band 2.2 µm). The simu-
introduce phase delay between the re-          lated values include an error budget which probably explains why the laboratory curve shows
combined beams during close loop op-           better performance. The straight dashed-dot line shows the Strehl ratio in open-loop.The
eration, which would limit fringe con-         crosses are the specifications issued by VLTI.
trast. This is extremely critical if it oc-
curs at high frequency, where the VLTI            A dedicated infrared camera working            In Figure 6 the blue curve shows the
delay lines are no longer able to detect       in K-band is installed permanently on          results of the simulations. The red curve
and correct for it. This is the reason for     the Test bench for characterization of         shows the values measured in the lab-
the strict piston specification: 25 nm         the resulting image quality and evalua-        oratory in Garching with simulated tur-
RMS in 48 msec windows.                        tion of the Strehl ratio.                      bulence. This shows a slightly higher
   The strategy has been described by             A second infrared test camera has           Strehl ratio, but the most interesting fea-
Vérinaud & Cassaing (2001) and in-             been fabricated for commissioning the          ture is that a trend very similar to the
volves defining a set of piston free influ-    four MACAO-VLTI and SINFONI as                 simulations is seen versus star magni-
ence functions. A special set-up using a       well. The design is simple and uses            tude. The curve may slightly shift left if
commercial Shack-Hartman WFS and a             three spherical mirrors. It uses a Hawaii      the whole system throughput (including
capacitive sensor allows one to meas-          1K chip and is controlled by an IRACE          telescope) is less efficient than what
ure accurately (better than 1%) the op-        system.                                        has been assumed (right if more). The
tical piston averaged over the DM pupil                                                       plot is for a 0.65 seeing. The crosses
for each electrode. The piston-free in-        Simulations & test results                     show the specifications issued by VLTI.
fluence functions are built by adding a            A whole set of simulations has been
pure piston to the original influence          carried out in order to predict the per-       Project organisation & future
function equal but opposite in sign.           formance of the system. The various
These are used to command the DM.              assumptions were a model of the at-            Tip-tilt boxes
The so-called tilt electrodes of the bi-       mosphere with three main layers,                  The milestone “Tip-Tilt Boxes
morph mirror (outside the pupil) con-          matching what is agreed to be the stan-        Delivery” was a partial delivery of the
tribute mostly to the production of a          dard average atmosphere in Paranal.            MACAO systems to accommodate the
pure piston.                                   The three layers are chosen to match a         VLTI planning. These are composed of
                                               seeing condition of 0.65 at 500 nm, t0 ~       the MACAO-VLTI opto-mechanical
Integration & test                             4 ms, wind speed ~11 m/s and r0 ~ 16           structure, including the XY tables, but
                                               cm. We have also tested one case of            without high order wavefront sensing
Test bench & facilities                        worse conditions, characterized by a           and wavefront correction capability. The
   A special effort was made to develop        seeing of 1 at 500 nm, t0 ~ 3 ms and r0 ~      TTB allows the observer to acquire
all necessary tools for a straightforward      10 cm. Two different values for the sky        stars, to track stars off-axis and per-
assembly and integration of the                background have been considered: mV            forms a tip-tilt correction of the source
MACAO systems. This has turned out             = 20.7 mag/arcsec2 (average dark sky)          (closed loop between STRAP & M2 mir-
to be justified since all together five sys-   and mV = 19 mag/arcsec2 (bright sky).          ror). This set-up was delivered to UT1
tems plus two Tip-tilt boxes (TTB) will            The reference flux for the simulations     and UT3 in November 2001 and has
have to be (have been) assembled and           is 4⋅105 detected photons/second at            been in use since then. They will ulti-
integrated in the life of this project.        magnitude 15 in the overall 8.2 m aper-        mately be replaced by full-fledged
   For AO integration and test aspects,        ture. We chose a value of 250 cps for          MACAO systems. Tests carried out on
a complete Test bench has been de-             the APDs’ dark current, from the Perkin-       an 11.7 mag star show a ~10 mas tilt
signed and fabricated. This bench re-          Elmer commercial list. The membrane            residual after correction.
produces an f/46.7 optical beam, identi-       stroke used is 0.25 m minimum (focal
cal to a Coudé focus. The source mod-          length) and a 500 µsec computing delay         Project aspect
ule provides alignment sources (laser)         was assumed. Different configurations             It is worth mentioning that, in addi-
and various set of target for the align-       of sub-apertures and electrodes geom-          tion to MACAO-VLTI, SINFONI and
ment of MACAO-VLTI with respect to             etry have been envisioned. The one             CRIRES also use similar AO compo-
the bench. A turbulence generator using        adopted minimizes the total noise vari-        nents. The implications are that several
phase screens produces a turbulent             ance and the variance of noise on the          components can be ordered in several
wavefront.                                     tilt correction.                               copies (usually 7 up to 10) leading to a

10
                                                                                                       absorbing filters was used to simulate
                                                                                                       fainter stars.
                                                                                                          Figure 7 shows a diffraction-limited
                                                                                                       K-band image of a bright star V = 9.86
                                                                                                       (HIC 69495) obtained in April. Three
                                                                                                       diffraction rings can clearly be seen and
                                                                                                       the FWHM image resolution achieved
                                                                                                       in 0.8 seeing was 60 mas with a Strehl
                                                                                                       ratio above 50%. Also shown is the
                                                                                                       moderate image improvement achie-
                                                                                                       ved using a faint (V = 16.5) guide star.
                                                                                                       In 0.55 seeing, the corrected K-band
                                                                                                       image resolution was 140 mas with a
                                                                                                       Strehl ratio of 10%.
                                                                                                         Figure 8 shows images of HIC 59206
Figure 7: On the left is a K-band image of a bright star (V~10) obtained in average seeing con-       (V = 9.9) taken in 0.75 seeing condi-
ditions (0.8 ). Three diffraction rings can clearly be seen with a Strehl ratio larger than 50% and   tions, illustrating the improvement of the
a FWHM of 60 mas. The plot on the right demonstrates the faint guide star performance. Using          image resolution when using MACAO-
a V = 16.5 star, a K-band Strehl ratio of 10% and a FWHM of 140 mas were achieved in 0.55             VLTI. The left image was taken in open-
seeing. The three dimensional plots also show the open loop images for comparison.                    loop (seeing limited), while the adaptive
                                                                                                      optics loop was closed during the expo-
                                                                                                      sure shown on the right. The separation
                                                                                                      of the binary is 0.12 .

                                                                                                      Astronomical targets
                                                                                                         A few interesting objects, from an as-
                                                                                                      tronomical point of view, were selected
                                                                                                      to illustrate the performance of
                                                                                                      MACAO-VLTI. It must be pointed out
                                                                                                      that the aim of MACAO is not to pro-
                                                                                                      duce astronomical images (the Test
                                                                                                      Camera is by no means a high per-
                                                                                                      formance scientific instrument) but
                                                                                                      rather to feed light to the VLTI. The fol-
                                                                                                      lowing images allow comparison with
                                                                                                      other instruments. Results are impres-
                                                                                                      sive and compare advantageously to
                                                                                                      other AO systems with higher number of
Figure 8 shows K-band images of a V=10 star obtained – before (left) and after (right) the            actuators.
adaptive optics was switched on. The separation of the binary is 0.12 and the seeing at the
time of observation was ~0.75 (see the text).                                                         Frosty Leo
                                                                                                         Frosty Leo is a post-AGB star sur-
                                                                                                      rounded by an envelope of gas, dust,
substantial cost reduction but also cre-           Sky observations                                   and large amounts of ice (therefore the
ating some motivation in industry.                                                                    name) displaying a bipolar morphology.
Besides, work or tasks accomplished                Goal                                               It is one of the best examples of the
on a particular project often benefit the            The main goal of the April 2003 com-             brief transitional phase between the
other which leads to a non-negligible              missioning was to test the functioning of          asymptotic giant branch (AGB) and
gain in development.                               the whole system in the telescope envi-            planetary nebulae (PNe). For a three
                                                   ronment and evaluate the AO perform-               solar mass object, this transitional
                                                   ance on the sky. These were voluntarily            phase is believed to last only a few
Schedule                                           decoupled from any interferometric
    The fast-track nature of the project is        functions and aim at assessing the per-
illustrated by the fact that Tip-tilt boxes        formance of MACAO-VLTI in stand-
delivery took place in November 2001,              alone mode. Further commissioning
barely 7 months after the final design             runs will take care of the interferometric
review. Then the first MACAO-VLTI sys-             aspects.
tem was delivered last April, and the
second will be delivered in August 2003.           Strehl ratio & resolution
Shortly afterwards, a joint team of the                After we were re-assured on the ba-
AO dept. and VLTI will perform a joint             sic functions of the system like source
commissioning to obtain fringes with               acquisition, closing of the loop, and sta-
two MACAO-VLTI systems. The last                   bility, the performance evaluation activ-
two MACAOs will be delivered not be-               ities started. This constituted an impor-
fore spring 2004 and winter 2004.                  tant part of this run and consisted in ob-
    The interval between the successive            serving a star (point source) while vary-
MACAO-VLTI deliveries is dictated by               ing the parameters of the system in or-
the manpower available to perform the              der to obtain the highest possible Strehl          Figure 9 shows a 5 i5 K-band image of
integration and optimisation of the sys-           ratio. The parameters that can be ad-              Frosty Leo taken in 0.7 seeing. Although
tems. However, the commissioning                   justed are the closed-loop main gain               Frosty Leo is rather bright (V=11), it is a dif-
schedule in Paranal is extremely busy              and the stroke of the vibrating mem-               ficult AO target because of its extension of
in 2004 and this may add further con-              brane. These are known to depend on                about 3 at visible wavelengths. The cor-
straints on the actual delivery dates.             source extend and brightness. A set of             rected image quality is about 0.1 FWHM.

                                                                                                                                                  11
thousand years, just a wink in the life of                                                        Summary
the star. Hence, post-AGB objects are
very rare, and Frosty Leo is one of the                                                              The AO department of ESO has com-
nearest and brightest among them (see                                                             pleted the design of an adaptive AO
Figure 9).                                                                                        system for the VLT Interferometer.
                                                                                                  Ordering of components, manufacturing
NGC 3603                                                                                          and integration took place in 2001 and
   Among the first objects observed was                                                           2002. The system is built in four copies,
the stellar cluster NGC 3603 located in                                                           one for each VLT. It is installed at the
the Carina spiral arm of the Milky Way                                                            Coudé room and the Coudé train is
at a distance of about 20,000 light-years                                                         used as a “science path”. Only one of
(see Figure 10). With its central star-                                                           the mirrors (M8, pupil conjugated) is re-
burst cluster, it is one of the densest and                                                       placed by the corrective optics. The 60
most massive star forming regions in                                                              elements system should allow a Strehl
our Galaxy. Some of the most massive                                                              ratio of ~0.6 on bright sources.
stars - with masses up to 120 times the                                                              Commissioning activities started in
mass of our Sun - can be found in this         Figure 11 displays a K narrow-band image of        April 2003 and the delivery of the 4th
cluster.                                       the massive star Eta Carinae. The image            system is planned for late 2004. At the
                                               quality is difficult to estimate because the       time of this writing the first commission-
                                               central star saturated the detector, but the       ing of the first MACAO has been com-
                                               clear structure of the diffraction spikes and      pleted and results are encouraging. The
                                               the size of the smallest features suggest a        integration and test phase of the 2nd
                                               nearly diffraction limited performance. The        system is in full swing.
                                               field measures roughly 6.5 i 6.5 arcsec.

                                                                                                  References
                                               light years away), Eta Carinae briefly
                                               became the second brightest star in the            Bonnet, H., et al. 2002, Proc. SPIE 4839:
                                               sky with an apparent magnitude of –1.                 Adaptive Optical System Technologies II,
                                                                                                     “Implementation of MACAO for SINFONI
                                               The Galactic Centre                                   at the Cassegrain focus of VLT, in NGS
                                                                                                     and LGS modes”
                                                  The centre of our own galaxy (Figure
                                                                                                  Donaldson, R. et al., 2000, Proc. SPIE 4007,
                                               12) is located in the Sagittarius constel-            p.82-93, “MACAO and its application for
                                               lation at a distance of approximately 8               the VLT interferometer”
                                               kpc from Earth. Recent AO observa-                 Glindemann, A., et al., 2002, Proc. SPIE
                                               tions using NACO at the VLT provide                   4838:     Interferometry     for    Optical
Figure 10 displays a K-band image of the       compelling evidence that a supermas-                  Astronomy II
starburst cluster NGC 3603. MACAO-VLTI         sive black hole with 2.6 million solar             Moorwood, A.F.M., et al., 2002, Proc. SPIE
compensated atmospheric disturbances by        masses sits in the centre (Schödel, R.,               Astronomical Telescopes and Instru-
                                               Ott, T., Genzel, R. et al., 2002; see also            mentation, “CRIRES: a high-resolution in-
analyzing light from a star which was 30
                                                                                                     frared spectrograph for the VLT”
separated from the field centre. The stellar   the March 2003 issue of The Mes-
                                                                                                  Roddier, F., 1988, “Curvature sensing and
images have a Full-Width-Half-Maximum          senger). This result, based on astro-                 compensation: a new concept in adaptive
(FWHM) diameter of 0.1 arcsec. The field       metric observations of a star orbiting the            optics”, Appl. Opt., 23, 1223-5
measures 9 i 9 arcsec.                         black hole at only 17 light hours mini-            Schödel, R., Ott, T., Genzel, R. et al., 2002,
                                               mum distance, could not have been ob-                 Nature, 419, 694-696
                                               tained without imaging at diffraction lim-         Verinaud, C., Cassaing, F., 2001, A&A, 365,
                                               ited resolution.                                      314
Eta Carinae
   Eta Carinae (Figure 11) is one of the
most massive stars in the Universe,
probably more than 100 solar masses.
It is about 4 million times brighter than
the Sun, making it one of the most lu-
minous stars known. As such massive
stars have a comparatively short ex-
pected lifetime of roughly 1 million
years, Eta Carinae must have formed
recently in the cosmic timescale. Eta
Carinae is also highly unstable and
prone to violent outbursts caused by the
fact that its high mass causes an ex-
tremely high luminosity. This leads to a
high radiation pressure at the star's
“surface”, which blows significant por-
tions of the outer layers off into space,
in a slow but violent eruption. The last of    Figure 12 shows a 90 second K-band exposure of the central 6 i13 around the Galactic Centre
these outbursts occurred between 1835          taken in 0.8 seeing, i.e., under average atmospheric conditions. Although the V=14.6 guide star
and 1855 and peaked in 1843, when,             is located roughly 20 from the field centre, leading to isoplanatic degradation of image quality, it
despite its distance (7,500 to 10,000          is nearly diffraction limited with a point source FWHM of about 0.130 .




12
MIDI Combines Light from the VLTI:
the Start of 10 µm Interferometry at ESO
CH. LEINERT 1, U. GRASER1, A. RICHICHI 2, M. SCHÖLLER 2, L. F. B. M. WATERS3,
G. PERRIN4, W. JAFFE 5, B. LOPEZ 6, A. GLAZENBORG-KLUTTIG7, F. PRZYGODDA1,
S. MOREL2, P. BIEREICHEL2, N. HADDAD 2, N. HOUSEN 2, A. WALLANDER 2
1MPI für Astronomie, Heidelberg, Germany; 2ESO, Garching, Germany; 3Astron. Institute Univ. of Amsterdam,

Netherlands; 4Obs. de Paris-Meudon, France; 5Sterrewacht Leiden, Netherlands; 6Obs. de la Côte d’Azur, Nice,
France; 7ASTRON, Dwingeloo, Netherlands
   When at the beginning of November          glows brightly! There is no distinction          tinely and reliably on several stars. This
2002 the MIDI containers were opened          between day and night, and even the              success might give the impression that
up in Paranal and the team members            brightest stars are just tiny speckles of        things were relatively simple. In reality,
together with ESO personnel started to        light in an overwhelmingly bright back-          it was quite the opposite.
assemble the instrument in the VLTI in-       ground. For this reason, previous at-
terferometric laboratory, nobody could        tempts to perform interferometry in the          Some history
be completely sure that their ambitious       thermal infrared had to find other ways
goal could actually be achieved: to bring     to combine the light (for example, like             When in January 1997 scientists at
together for the first time two beams of      Bester et al. (1990), in the style of ra-        the Max-Planck-Institut für Astronomie
light from distant giant telescopes at the    diointerferometers, thereby however              in Heidelberg (MPIA) were sitting to-
wavelength of 10 microns and obtaining        sacrificing sensitivity), or never achie-        gether to think about how to react to
stable, repeatable and accurate inter-        ved a real routine operation. Even the           ESO’s call for proposing interferometric
ference fringes. Although the instrument      ambitious efforts being carried out at           instrumentation for the VLTI, it was not
had been designed and built with the ut-      the Keck Interferometer, in spite of hav-        clear for which wavelength range they
most care and all laboratory tests in         ing started earlier than at ESO, are so          should propose to build an instrument.
Europe indicated that all specifications      far still confronted with difficulties in this   The near-infrared range around a wave-
were met, going to the sky was another        special area.                                    length of 2 µm had the advantage of be-
matter. The thermal infrared covers the          It was indeed a big satisfaction when,        ing a proven high-quality observing
wavelength range around the peak of           after a few weeks of integration, MIDI           method with detector arrays on many
the natural emission of a black body          achieved first fringes on the small              telescopes. Observing in the wave-
with a temperature about 300 K. This is       siderostat telescopes first, and on the          length region around 10 µm, the main
close to the ambient temperature of the       large Unit Telescopes immediately af-            mid-infrared atmospheric transmission
telescope mirrors and structure, of the       terwards. This encouraging result was            window, at first view appears laden with
two dozens of mirrors (in each arm)           immediately reported in an ESO Press             disadvantages: the thermal emission of
needed to bring the light into the tunnel     Release (25-02) and a press release by           the room temperature surroundings is
and the interferometric lab, of all the       the MPIA in Heidelberg (02-12-19).               at its maximum, about 10 W/m2/sr/µm,
mechanic structures, and of course of         After that, a First Commissioning run            by many orders of magnitude higher
the sky. Therefore, at the wavelengths        has also been completed in February              than the expected typical signal from a
to which MIDI is sensitive, everything        2003, with fringes being obtained rou-           star, and the long wavelength of 10 µm
                                                                                               will limit the spatial resolution achiev-
                                                                                               able on the VLT Interferometer - and
                                                                                               given by the ratio of λ/baseline - to a
                                                                                               value five times smaller than for near-in-
                                                                                               frared wavelengths. On the other hand,
                                                                                               the mid-infrared wavelength range has
                                                                                               its attractive sides, too. It is a tracer of
                                                                                               material at temperatures of a few hun-
                                                                                               dred K, at which 10 µm radiation is emit-
                                                                                               ted most efficiently. Such material is in-
                                                                                               timately connected to young stars in the
                                                                                               form of discs or circumstellar en-
                                                                                               velopes, to giant stars in dust shells
                                                                                               formed from expulsion of surface layers
                                                                                               and in Active Galactic Nuclei as tori con-
                                                                                               fining the space around the central
                                                                                               massive black holes - all of them areas
                                                                                               of high current research interest. The
                                                                                               higher penetrating power of the longer
                                                                                               wavelength is an additional advantage
                                                                                               in studying these often rather dense
                                                                                               clouds of material. And a 10 µm inter-
                                                                                               ferometric instrument using the full
                                                                                               available atmospheric transmission
                                                                                               window from 8 µm to 12 µm would have
                                                                                               been the first of its kind worldwide. In
                                                                                               the end, the enthusiasm for a totally
Figure 1: The fully assembled MIDI instrument in the interferometric laboratory on Paranal     new field of observations won over the
during commissioning in February.                                                              risks and challenges, and the acronym

                                                                                                                                       13
“MIDI” (Mid-infrared Interferometric in- this software work, not further described an intermediate focus is formed, where
strument) carries with it the chosen here, can hardly be overestimated. different slits or diaphragms (i.e. spatial
wavelength range.                                Mostly hidden to the outside and requir- filters) can be introduced for additional
   Looking back, those days now seem ing intense cooperation between the in- suppression of unwanted radiation. If no
history. MIDI was transported to strument and the VLTI software teams, spatial filters are used, the detector pix-
Paranal in October 2002, packed in 34 the development of specialized soft- els, which are much smaller than the
boxes with a total weight of nearly 8 ware is at the heart of the MIDI project. Airy disc, still provide an alternative way
tons. The assembly and installation be-             It should be noted here that MIDI to limit the spatial region admitted for
gan on November 4, and from started off as a specialised PI-instru- the measurement. Then the beams are
November 15 to 27, they were followed ment and only after Concept Design recollimated (again, reflective optics is
by an extensive alignment and verifica- Review was changed to a fully compli- represented by a lens for simplicity) and
tion phase in the interferometric labora- ant VLT instrument, following ESO stan- move on to combine on the surface of a
tory. Finally MIDI went to the sky. After dards as far as possible and with the 50-50 beam splitter, situated close to
several nights of testing with the 40 cm ambitious goal to be operated in a rou- the reimaged pupil plane. The active
siderostats MIDI eventually was con- tine and user-friendly fashion like any coating is indicated in the Figure on the
nected to the Coudé beams of ANTU other instrument on Paranal. This is a lower half of the back side of the ZnSe
and MELIPAL and in the second of two bold goal for an interferometric instru- plate. This is the heart of the instrument.
nights, the 15th of December, MIDI de- ment. As a result of this history, unlike                    From the beam combiner onwards,
tected its first fringes with the VLT tele- all other first generation ESO VLT in- the two interfering beams have a com-
scopes.                                          struments, in the MIDI project essential- mon optical axis. Actually, there are two
   This moment was full of emotion for ly all of the hardware was paid for by the such overlaid beams, one outgoing to
the people present and all their col- MIDI consortium. ESO also developed each side of the beam combiner. These
leagues back in Europe: it culminated and provided specialized hardware two outputs are modulated in flux de-
an effort of over 5 years. Indeed, the needed to integrate MIDI into the VLTI. pending on the optical path difference of
first solid step of planning a mid-infrared The total cost of MIDI born by the con- the interfering beams, but with opposite
instrument for the VLTI began at MPIA sortium - not counting the necessary sense because of energy conservation.
in summer 1997: it was the beginning of matching efforts on ESO’s side - is of Next, an image of the sky is formed for
a road which led to the “Preliminary the order of 6 million Euros. Of this, 1.8 each of the two combined beams on the
Acceptance Europe” (PAE) in Sept- million Euros are for equipment, materi- detector. Spectral information can be
ember 2002.                                      als and optical parts, with the remaining obtained by inserting filters or by spec-
   Besides the MPIA, which is leading for salaries during the extensive plan- trally dispersing the image using a
the effort with a PI team (project scien- ning, construction and testing.                        prism for low or a grism for intermediate
tist and project manager) and providing                                                          spectral resolution. If it is required to
cryogenics, mechanics, control and The instrument                                                monitor the flux in the incoming tele-
system software, detector including                                                              scope beams for high precision meas-
read-out electronics and associated Principle of measurement                                     urements, beam splitters can be insert-
software, major and important contribu-             The optical concept of the instrument ed in front of the beamcombiner unit.
tions came from the Netherlands, is shown in Figure 2. From the left, the The resulting additional monitoring
France, and other German institutes:             afocal beams from two telescopes of beams are imaged onto the same de-
   – the cold optics from ASTRON the VLTI are approaching the instru- tector.
(Dwingeloo), the near-real-time soft- ment. Their nominal diameter is 80 mm,                        MIDI measures the degree of coher-
ware, the templates to run the instru- and they are reduced to 18 mm diame- ence between the interfering beams
ment and the software management ter by a beam compressor provided as (i.e. the object visibility at the actual
from NEVEC (Sterrewacht Leiden) as part of the VLTI infrastructure, repre- baseline setting) by artificially stepping
Dutch contributions,                             sented here for simplicity by two lenses. the optical path difference between the
   – the data reduction software, man-              After the four folding mirrors of a two input beams rapidly over at least
agement of the instrument science small internal delay line, the com- one wavelength within the coherence
group (OCA, Nice) and efforts to pro- pressed beams enter the cryostat time of ~ 0.1 s. This is done with help of
vide MIDI with a 10 micron monomode (“Cold box”) through the entrance win- the piezo-driven roof mirrors forming
fibre as spatial filter (Observatoire de dow (“Dewar window”). The telescope part of the small delay lines just outside
Paris) from France,                              pupil is imaged by the VLTI delay line the cryostat. The result in both channels
   – the warm optics from the optics onto a cold pupil stop to provide is a signal modulated with time (“tem-
Kiepenheuer-Institut für Sonnenphysik the needed suppression of thermal poral fringe”), from which the fringe am-
(Freiburg) and preparation of interfero- emission from outside the beams. Next, plitude can be determined. The large
metric calibrators from the
Thüringer Landessternwarte
                                    Table 1: Basic parameters of the instrument
(Tautenburg).
   Last but not least one             Wavelength coverage                      N band (8 - 13 µm )            expandable to Q (17 - 26 µm)
should emphasize the crucial          Resolution (λ/B for 100 m)               20 milli-arcsec
collaboration with ESO per-           Spectral resolution                      up to 300                     (prism, grism)
sonnel both in Garching and           Airy disc (FWHM) at 10 µm                0.26 (for UTs)                (FOV = 2 )
Paranal in all areas of the                                                    1.14 (for ATs)
project.                              Sampling time for fringe motion          100 ms ... 1 sec              average ... best conditions
   The work carried out by the        Atmospheric stability for chopping       200 ms
consortium covered a very             Detector                                 50 microns                    pixel size
wide range of topics, from the                                                 320 x 240 pixels              dimensions
design and realisation of opti-                                                2 x 107 electrons             full well
cal and mechanical concepts,                                                   800 electrons                 read noise
to the demanding task of pro-         Background noise from sky                1.6 x 1010 photons/sec
                                         from VLTI (at UT in Airy disc)        1.23 x 1011 photons/sec
viding the complex software
                                      Limiting N-magnitude
needed to run the instrument
                                         (without/with external                at UTs 3-4 mag (1-2.5 Jy)     /7-9 mag (0.1-0.6 Jy)
as integral part of the VLTI.             fringe tracking)                     at ATs 0-1 mag                /4-6 mag
The importance and size of

14
Figure 2:
Schematic
diagram of the
instrument.
For explanation,
see text.




and not precisely known thermal back-         introduced by the very high and variable       the high background is corrected for by
ground forces us to determine the total       background at 10 µm (see Table 1).             chopping of the telescope and thus sub-
flux separately by a chopped measure-         With such a high background resulting          tracting the background. This also holds
ment, chopping between the object and         mainly from all the warm optical ele-          for interferometry where the knowledge
an empty region of the sky, and deter-        ments in the VLTI chain the detector           of the two beam intensities is needed
mining the source flux by subtraction.        pixels would be saturated very quickly         for the accurate calculation of the ob-
The raw normalised visibility is obtained     after several milliseconds. So, only dis-      ject’s visibility. In MIDI the two photo-
by dividing the fringe amplitude by the       persing of the signal over a number of         metric channels (see Figure 2) were
total flux. As in standard interferometric    pixels prevents saturation. The typical        foreseen for delivering this information.
practice, the calibrated visibility is ob-    integration times for MIDI therefore are       However, when the external fringe-
tained by dividing the raw visibility of an   in the range of one to several hundreds        tracker and the adaptive optics are in
object by that of a known star.               of milliseconds. It is clear that this could   operation, chopping will impose signifi-
                                              lead to a very high data rate of up to         cant losses in time efficiency and addi-
Critical points and basic features            some tens of Mbytes/sec. By windowing          tional synchronization constraints. This
   In the planning phase of MIDI three        the frames during detector read-out the        mode remains to be tested extensively
major technical fields were identified        most important operating modes will not        in the next commissioning runs.
that could at the end turn out to become      exceed a pure read-out time of 3 msec             A third major concern was the accu-
a show-stopper or at least create some        and a final data rate of 3 Mbyte/sec           racy of the alignment, and in particular
constraints for the technical develop-        which is compliant with the current ca-        how the alignment of the cold optical el-
ment of MIDI: vibrations, detector read-      pabilities of the ESO archiving system.        ements, which can only be performed in
out, and alignment.                           Developing this detector readout system        the warm when the devices are acces-
   Vibrations are a natural consequence       with the real-time synchronisation capa-       sible for adjustment, is maintained dur-
of the fact that MIDI had to apply a          bilities needed for self-fringe tracking       ing cooling. Two major steps have been
closed cycle cooler for cooling the op-       was one of the major tasks of instrument       taken to overcome this difficulty. First:
tics to below 40 K and the detector to        development (see Ligori et al. 2003).          the whole cold optical bench including
below 10 K. At the time when MIDI was            Normally with instruments working in        its mountings have all been made out of
planned this was the only option to           the mid-infrared regime the variability of     parts of one single block of aluminium
guarantee the necessary cooling power.
Over more than two years extensive
tests were carried out with several de-
war set-ups to find possibilities to damp                                                                         Figure 3: MIDI’s Cold
these vibrations both in the MIDI instru-                                                                         Optical Bench (COB)
ment itself and in the environment                                                                                inside the open de-
where we had to avoid disturbing neigh-                                                                           war. The two radia-
bouring instruments. Finally we ended                                                                             tion shields are visi-
up with a design that concentrates on a                                                                           ble around the opti-
very heavy (650 kg) separate mount for                                                                            cal setup which is
the cold head and we connected it to                                                                              cooled down with the
the MIDI vacuum by a metallic bellow                                                                              Closed Cycle Cooler
selected for its damping properties.                                                                              (on the left side in
Naturally, a number of additional techni-                                                                         the background) to a
cal measures such as special damping                                                                              temperature of 40 K.
feet had to be applied until we came up                                                                           The filter wheel
with a solution where the internal jitter                                                                         (black), focus and
on the detector would not exceed 0.04                                                                             other parts can be
pixel.                                                                                                            moved with the eight
   Another critical point for MIDI con-                                                                           motors at the sides
cerns the necessary fast read-out times                                                                           of the instrument.

                                                                                                                                    15
alloy, and they were designed in a way            ter at mid-IR-wavelengths (8–13 µm)               erating modes. At present, the first com-
that the shrinking of the material of                – Principle of measurement: The                missioning has been completed and al-
0.42% which comes from cooling down               beams from two telescopes meet on a               ready encouraging results can be pre-
from 300 to 40 K is nearly homologous             beam-combining beam splitter, where               sented.
and should keep the optical character-            their pupils are superimposed “on axis”.              Figure 4 shows the signals of the two
istics (see Glazenborg-Kluttig et al.                – The intensity of the two comple-             interferometric output channels ob-
2003). Second: A dewar mount was                  mentary outputs is modulated by step-             tained during an observation of Eta
constructed which is movable around               ping the optical path difference through          Carinae using the VLT unit telescopes
five of its six axes and thus provides for        one or more wavelengths by means of               ANTU and MELIPAL (UT1 and UT3).
an accurate adjustment of the heavy               an internal piezo-driven delay line.              The circular fields are dominated by
(230 kg) MIDI dewar. During the inte-                – a grism and a prism provide a spec-          background radiation from the sky and
gration and the first commissioning we            tral resolution up to 300.                        the VLTI tunnels. Only because the ob-
were very glad to find the concept of the            – phase measurement will occur                 ject is very bright (flux more than 5000
MIDI alignment to be fully confirmed. A           eventually by external referencing                Jy in the core, one of the brightest in the
view into the cold optics in the open de-         (when the dual beam capabilities of               sky at 10 µm) is it identifiable in MIDI’s
war is given in Figure 3.                         PRIMA become available on the VLTI).              FOV of 2 arcsec. Usually an object be-
   The outcome of all of these phases of                                                            comes distinguishable only after the
planning, design and development has              MIDI on Paranal: first results                    background is subtracted by chopping
been presented recently (Leinert,                 and scientific programme                          and nodding procedures. Chopping is
Graser et al. 2003a, 2003b, Przy-                                                                   performed by a modulation of the sec-
godda et al. 2003). Here is a summary               Currently the MIDI instrument is in a           ondary mirror with a frequency of about
description of the main characteristics of        phase of extensive tests during the first         2 Hz and an amplitude of 3 arcsec. The
the instrument (see also Table 1):                commissioning runs at Paranal to verify           resulting image in case of the observa-
   – Two beam pupil-plane interferome-            the function of the instrument in all op-         tion of Eta Carinae is shown in Figure 5.
                                                                                                    One can clearly identify the complex
                                                                                                    structure of the object. The image, ri-
                                                                                                    valling in sharpness the best mid-in-
                                                                                                    frared images obtained with dedicated
                                                                                                    imaging instruments on Mauna Kea,
                                                                                                    demonstrates the excellent imaging ca-
                                                                                                    pabilities of MIDI and the whole VLTI in-
                                                                                                    frastructure which sends the light via 31
                                                                                                    mirrors and 5 transmissive elements
                                                                                                    until it reaches the detector.
                                                                                                        When searching for the fringe signal,
                                                                                                    the large delay line of the VLTI infra-
                                                                                                    structure is moved in steps of 30 micron
                                                                                                    over a range of a few millimetres, while
                                                                                                    MIDIs internal piezo-driven delay line is
                                                                                                    performing additionally a few scans of
                                                                                                    60 micron each at each of those steps.
                                                                                                    At the position where the optical path
                                                                                                    difference (OPD) between the two inter-
Figure 4: Raw images of the very bright infrared object η Car during telescope pointing. Left:
                                                                                                    ferometric arms is almost zero, the
beam from UT1, right: beam from UT3. On the detector the two beams are at top and at bot-
                                                                                                    fringe signal from the object becomes
tom, separated by unexposed parts of the array. In these exposures, no field limitation has
                                                                                                    detectable in the subtraction of the two
been introduced except that given by the mechanical openings in the instrument. The outer,
                                                                                                    interferometric output channels. As an
bright ring is thermal emission from the VLTI tunnel and outside the field-of-view. The field-
                                                                                                    example, Figure 6 shows the superpo-
of-view through the VLTI to the colder sky (about 2 ) is seen as the darker inner circular struc-
                                                                                                    sition of five consecutively measured
ture. It is less pronounced for the beam from UT1 because at the time of this exposure there
                                                                                                    fringe packets, showing that fringe mo-
was some vignetting, increasing the contribution of unwanted thermal emission. η Car is
                                                                                                    tion can be quite small under good see-
bright enough to be seen already in these raw images.
                                                                                                    ing conditions. Fringe detection was
                                                                                                    performed also on a 9 Jansky source
                                                                                                    without problems, but finally the limiting
                                                                                                    magnitude of the instrument in self
                                                                                                    fringe tracking mode is not expected to
                                                                                                    be better than 1 Jansky, due to the fluc-
                                                                                                    tuations in the very strong background
                                                                                                    radiation. To increase the sensitivity it is
                                                                                                    necessary to apply external fringe track-
                                                                                                    ing. This possibility will be given by
                                                                                                    FINITO, which will be installed on
                                                                                                    Paranal later this year. Together with
                                                                                                    the adaptive optics system MACAO, it is
                                                                                                    expected to dramatically increase
                                                                                                    MIDI’s sensitivity.
                                                                                                        The scientific potential of MIDI has
                                                                                                    been discussed by the instrument sci-
                                                                                                    ence group and presented by
                                                                                                    Lopez et al. (2000). Further discussions
Figure 5: Chopped images of η Car obtained during the centring process. Left: beam from             led to a guaranteed time programme to
UT1, right: beam from UT3. The size of the blobs is close to the diffraction limit for 8-m tele-    fill the 300 hours of guaranteed observ-
scopes, about 0.25 . Note the good optical quality.                                                 ing time available to the instrument

16
Figure 6: The superpo-                                                                         FINITO should increase the sensitivity
sition of five fringe                                                                          of the highly background-limited instru-
packets, measured at                                                                           ment MIDI by at least a factor of 10 –
intervals of ~ 0.3 s and                                                                       even a factor of 80–100 appears possi-
their average plotted                                                                          ble. This will increase dramatically the
against the optical path                                                                       number of interesting objects to be
difference (OPD).                                                                              studied. Next, a proposal has been sub-
Here, the packets were                                                                         mitted to the funding agencies to allow
obtained in the fringe                                                                         an extension of MIDI operation into the
searching mode. The                                                                            20 µm wavelength range. Also, the pos-
fringe tracking mode                                                                           sibility is being studied to inject beams
allows one to adjust                                                                           from more than two telescopes simulta-
the delay lines                                                                                neously into the MIDI instrument by
automatically in order                                                                         means of an additional special external
to compensate the at-                                                                          optics rearranging the geometry of the
mospheric OPD varia-                                                                           input beams (Lopez et al. 2003). This
tions. Then, the object                                                                        would allow one to derive from the in-
visibility can be                                                                              terferometric measurements the so-
obtained with high accuracy by averaging the amplitude of hundreds of packets.                 called “closure phases” and thus enable
                                                                                               the reconstruction of images. An alter-
team on the UTs, which is shown in              of the VLTI will provide only a few meas-      native way for image reconstruction
Table 2. This list gives an impression of       ured points of visibility, in a reasonable     may open two years from now, when
what may be feasible to observe with            time of several hours, i.e. only a few         the VLTI will have installed the PRIMA
the MIDI instrument. It has to be kept in       points where the Fourier transform of          “dual-beam” facility which will allow one
mind that the objective of direct planet        the object image is determined. The sci-       to freeze the fringe motion at a particu-
detection is atypical. It tries to detect the   entific programme has to be checked in         lar position such that the phases neces-
very small shift with wavelength of the         advance as to whether its main ques-           sary for image reconstruction can be
centre of the combined image of star            tions can be answered on this basis            obtained even in normal operation of
and planet. Requiring a differential ac-        (e.g. to determine the diameter of a star      MIDI with two-beam combination. Mid-
curacy of 10–4, not guaranteed to be at-        one does not need to construct an im-          infrared interferometry promises to be-
tainable by the instrument, it is a pro-        age of its surface). As an example             come a field with much wider applica-
gramme of extremely high risk for pos-          Figure 7 shows a prediction for the            tions during the next decade. But the
sibly high reward.                              close young binary Z CMa. Here, the            most exciting time for those having
   When planning observations with              existence of circumstellar discs around        been involved in the instrument devel-
MIDI, a few constraints have to be kept         the two components will show in a              opment is now: the first steps into new
in mind. For self-fringe tracking, not only     strong reduction with telescope separa-        territory.
must the source be bright enough but            tion of the sinusoidal visibility variations
there must be sufficient flux in a very         typical for a binary source. Such a sig-       Acknowledgments
compact (<0.1 ) central region, to which        nature can be clearly identified with a
the interferometric measurements will           limited set of VLTI observations.                 The dedicated efforts of a large num-
refer. In general, the visual brightness                                                       ber of colleagues from the institutes in-
should be at least 16 mag, in order to al-      The near future                                volved were necessary to bring the in-
low the operation of the tip-tilt and                                                          strument MIDI to its present state of
MACAO adaptive optics system. For                  Now that MIDI is approaching routine        completion, in addition to the few who
observations with external fringe track-        observations as a science instrument           are honoured as authors of this article.
ing, the H-band brightness should be at         on Paranal, have we exhausted the po-          We very much want to thank all of those
least 11 mag in order to drive the fringe       tential of 10 µm interferometry? Quite         for their important work and helpful co-
tracker. In addition, one has to consider       certainly not. A year from now, external       operation and apologise if someone’s
that interferometry with two telescopes         fringe stabilisation by the fringe tracker     name should be missing in the following
                                                                                               list of contributing persons:
Figure 7: Simulation of                                                                        • from MPIA Heidelberg:
an observation of the                                                                             H. Baumeister, H. Becker, S.V.W.
young binary Z CMa.
                                                                                                  Beckwith (now STScI), A. Böhm, O.
                                                                                                  Chesneau, M. Feldt, A. Glindemann
The binary has been                                                                               (now ESO), B. Grimm, T. Herbst, S.
represented by two point                                                                          Hippler, W. Laun, R. Lenzen, S.
sources at the observed                                                                           Ligori, R. J. Mathar, K.
separation of 0.1 at P.A.                                                                         Meisenheimer, W. Morr, R. Mundt,
300°, each surrounded                                                                             U. Neumann, E. Pitz, I. Porro (now
by a circular disc with                                                                           MIT), M. Robberto (now STScI), R.-
Gaussian brightness dis-                                                                          R. Rohloff, N. Salm, P. Schuller (now
tribution and FWHM of                                                                             Harvard-Smithsonian Center for
10 mas. From upper left
                                                                                                  Astrophysics), C. Storz, K. Wagner,
                                                                                                  K. Zimmermann
to lower right we see:                                                                         • from Astronomical Institute of the
the image of the object;                                                                          University of Amsterdam: R. van
its Fourier transform and                                                                         Boekel
the tracks covered by                                                                          • from ASTRON, Dwingeloo: S.
the telescope pairs UT1-                                                                          Damstra, J. de Haas, H. Hanenburg
UT3 (outer lines) and                                                                          • from Kapteyn Institute Groningen:
UT1-UT2; the observed                                                                             J.-W. Pel
visibility as function of                                                                      • from Sterrewacht Leiden: E. Bakker,
time (left) and of spatial
                                                                                                  W. Cotton (now NRAO), J. de Jong,
                                                                                                  J. Meisner, I. Percheron (now ESO),
frequency. Here, the                                                                              H. Rottgering
curves with the lower visibility values correspond to the longer baseline UT1-UT3.             • from Observatoire de Paris Meudon:

                                                                                                                                     17
Table 2: Proposed guaranteed time programme                                                      4838, 1171-1181, 2003
                                                                                              C. Leinert, U. Graser et al., “Ten-micron in-
          Topic                                            Telescopes                            strument MIDI - getting ready for observa-
                                                           UTs     ATs                           tions on the VLTI”, SPIE 4838, 893-904,
Dust Tori in Nearby Active Galactic Nuclei                 65 h      –                           2003a
Inner discs of low-mass young stellar objects              65 h     90 h                      Ch. Leinert, U. Graser et al., “MIDI - the 10
Inner discs around intermediate-mass young                                                       µm instrument on the VLTI”, Conf. Proc.,
                                                                                                 11th EAS Meeting: “JENAM 2002: The
         and Vega-type stars                               62.5 h    100 h
                                                                                                 Unsolved Universe”, Porto, Portugal,
Massive young stars                                        52.5 h    305 h                       Astrophys. Space Sci. 2003b
The dusty environment of hot stars                         2h         68 h                    S. Ligori, U. Graser, B. Grimm, R. Klein,
Cool Late Type Stars and related objects                   25 h      450 h                       “Experiences with the Raethyon Si: As
Extra-solar planets and brown dwarfs                       25 h       –                          IBC detector arrays for mid-IR interfero-
                                                                                                 metric observations”, SPIE 4838, 774-
                                                                                                 785, 2003
    J. Bonmartin, G. Chagnon, V. Coude          Glindemann, S. Guisard, B. Koehler,           B. Lopez, Ch. Leinert, U. Graser et al., “The
    du Foresto, M. Nafati (now Nice)            S. Levêque, J.-M. Mariotti (†), S.               astrophysical potentials of the MIDI VLTI
•   from Observatoire de la Côte d’Azur         Menardi, F. Paresce, J. Spyromilio,              instrument”, SPIE 4006, 54 - 67, 2000.
    Nice: P. de Laverny, G. Niccolini           M. Tarenghi (now ALMA)                        B. Lopez, Ph. Mathias, D. M’ekarnia et al.,
•   from Laboratoire d’Astrophysique                                                             “APres-MIDI, APerture Synthesis in the
    Grenoble: A. Dutrey                                                                          MID-Infrared with the VLTI”, SPIE 4838,
•   from Kiepenheuer-Institut für             References                                         1011 - 1015, 2003.
    Sonnenphysik Freiburg: L. Gantzert,                                                       F. Przygodda, O. Chesneau, U. Graser, Ch.
    O. von der Lühe, Th. Sonner, K.           M. Bester, W. C. Danchi, and C. H. Townes,         Leinert, S. Morel, “Interferometric obser-
    Wallmeier                                   “Long baseline interferometer for the mid-       vations at mid-infrared wavelengths with
•   from Thüringer Landessternwarte             infrared” SPIE 1237, 40 - 48, 1990.              MIDI”, Conf. Proc., 11th EAS Meeting:
    Tautenburg: B. Stecklum                   A. W. Glazenborg-Kluttig, F. Przygodda, H.         “JENAM 2002: The Unsolved Universe”,
•   from ESO: P. Ballester, B. Bouvier,         Hanenburg, S. Morel, J.-W. Pel,                  Porto, Portugal, Astrophys. Space Sci.
    C. Sabet, F. Derie, Ph. Gitton, A.          “Realization of the MIDI cold optics”, SPIE      (2003)




L. GERMANY, SciOps

Danish 1.54m Handover

   On September 30, 2002, ESO
stopped offering the Danish 1.54 m tel-
escope to its community. The Danish
1.54 m is now only available to the
Danish community, and ESO continues
to perform the maintenance of the tele-
scope. The main repository of informa-
tion regarding that telescope is now the
“Ground-Based Astronomical Instru-
ment Centre” (IJAF) at the CUO
(http://www.astro.ku.dk/ijaf/).


Final Dishwalk at the SEST

   March saw us witness the last ever                                                                             Lars-Ake Nyman and
dishwalk at the SEST telescope before                                                                             Mikael Lerner make the
its closure later this year. The SEST                                                                             final dishwalk on the
dish is inspected once a year for dam-                                                                            SEST.
age to the teflon coating. This may be                                                                            Photo by Lauri Haikala.
caused by pebbles flying around in high
wind (which cause small holes in the          be pointed close to zenith (since only          and the SEST has a 50 degree Sun
coating), high humidity, and from the         aliens can defy gravity to walk on the          avoidance zone. Pointing too close to
coating peeling off at the edges of the       dish when it is at low elevations). The         the Sun will fry the secondary (as hap-
panels. This damage is “fixed” by stick-      work has to be done bare foot (so as not        pened back in the 80’s), and walking
ing small plastic patches over the af-        to damage the delicate surface), and            around with bare feet on a metal sur-
fected area.                                  usually in the Chilean autumn, since the        face in the middle of summer is also
   To do the inspection, the dish has to      sun is high in the sky during summer            probably going to fry the inspectors!



18
                    REPORTS FROM OBSERVERS
Studying High Redshift Galaxy Clusters with the
ESO Distant Cluster Survey
G. RUDNICK1, S. WHITE1, A. ARAGÓN-SALAMANCA2, R. BENDER3,4, P. BEST 5,
M. BREMER 6, S. CHARLOT 1,7, D. CLOWE8, J. DALCANTON 9, M. DANTEL10,
G. DE LUCIA1, V. DESAI 9, B. FORT7, C. HALLIDAY 11, P. JABLONKA10, G. KAUFFMANN1,
Y. MELLIER7, B. MILVANG-JENSEN 4, R. PELLO12, B. POGGIANTI11, S. POIRIER10,
H. ROTTGERING13, R. SAGLIA3, P. SCHNEIDER 8, L. SIMARD14, D. ZARITSKY15
1MPA,  Garching, Germany; 2University of Nottingham, UK; 3Ludwig-Maximilian University, Munich, Germany;
4MPE, Munich, Germany; 5ROE, Edinburgh, UK; 6University of Bristol, UK; 7IAP, Paris, France; 8IAEF, University
of Bonn, Germany; 9University of Washington, Seattle, USA ; 10OPM, Paris, France; 11Osservatorio Astronomico
di Padova, Padova, Italy; 12OMP, Toulouse, France; 13Leiden Observatory, The Netherlands; 14HIA, Victoria,
Canada; 15Steward Observatory, Tucson, USA

   Galaxy clusters are the most massive       which can accrete onto the disc and           largest available sample at z ~ 0.4–0.5
quasi-equilibrium objects in the Uni-         form stars (strangulation; e.g. Larson,       has heterogeneous and poorly defined
verse and are the meeting places of the       Tinsley & Caldwell 1980); the HI can be       selection criteria, significantly compli-
cosmos. Their deep potential wells are        similarly stripped by motion through the      cating any comparison with theoretical
dominated by unseen dark matter, but          intra-cluster medium (ram-pressure            predictions. Finally, few clusters have
contain a cosmologically representative       stripping; e.g. Gunn & Gott 1972) or          been observed in detail at z ≥ 0.5 where
baryon fraction in the form of galaxies       may be used up in a brief star-burst trig-    evolutionary changes become dramatic.
and intergalactic gas. These are              gered by the high pressure cluster envi-         The time is ripe to significantly ad-
trapped in a virialized state, with the gas   ronment (stimulated star formation; e.g.      vance our understanding of galaxy evo-
heated to tens of millions of degrees         Dressler & Gunn 1983); and massive            lution in clusters. The basic theoretical
and the galaxies moving with rms ve-          galaxies may merge into a central su-         paradigm for structure formation is now
locities of ~1000 km/s.                       pergiant cD (cannibalism; White 1976).        well established on the relevant scales,
   The study of the evolution of galaxy       Theoretical treatments of these               and many of the important physical
clusters and of the galaxies within them      processes have improved dramatically          processes can be calculated reliably.
has largely been driven by observation.       as computer capabilities have ad-             Even more importantly, improved instru-
Starting in the late 1970’s a picture be-     vanced. Dark matter simulations can           mental capabilities allow quite precise
gan to emerge in which cluster galaxies       follow the formation of rich clusters,        data on the structure and stellar content
evolve towards redder colours with de-        tracking the evolution of substructures       of galaxies to be obtained out to red-
creasing redshift (Butcher & Oemler           as small as the halos of the faintest         shifts where evolutionary effects are
1978) and in which galaxy morpholo-           dwarf galaxies. The formation of the          large — at z ~ 0.8 where the universe
gies are biased towards ellipticals and       galaxies themselves can then be stud-         was less than half as old as it is today.
bulge-dominated systems in denser en-         ied by adding simplified treatments of
vironments (Dressler 1980). In the fol-       gas cooling, star formation, feedback,        The ESO Distant Cluster Survey
lowing years, imaging with the Hubble         and stellar evolution (e.g. Springel et al.
Space Telescope (HST) and spec-               2001).                                           We initiated the ESO Distant Cluster
troscopy with 4-meter class and larger           The wealth of observations now avail-      Survey (EDisCS), an ESO Large
telescopes confirmed and extended             able suggests that none of these              Programme, to take the next step in sur-
these early results, adding detailed in-      processes dominates the transforma-           veying the evolution of clusters and
formation about the spectral and mor-         tion of galaxies; all appear to play some     cluster galaxies. We aim to make a sys-
phological properties of galaxies out to      role, and they may have differing impor-      tematic study of cluster structure and
z ~ 0.5.                                      tance in different environments. Their        cluster galaxies out to z ~ 0.8 at a level
   A theoretical framework has devel-         interplay makes clusters ideal laborato-      of detail which will allow quantitative
oped for interpreting these observa-          ries for studying galaxy evolution. This      comparison with the large and statisti-
tions, based largely on simulations of        usefulness is enhanced by several             cally complete samples of nearby clus-
dynamical effects on cluster galaxies.        practical advantages. Clusters contain        ters being provided by the 2dF and, par-
As galaxies fall into clusters along the      many galaxies close together on the sky       ticularly, the SDSS projects. Our pro-
filaments which define large-scale            and at the same redshift, making effi-        gramme involves matched optical pho-
structure, the observed trends can be         cient observation easy with a modest          tometry from the VLT and near-IR pho-
imprinted by a variety of processes:          field of view and permitting the approxi-     tometry from the NTT, followed up by
galaxy morphologies may be altered by         mation that all cluster members are           multi-object spectroscopy using FORS2
repeated gravitational shocking through       equidistant from the observer.                on the VLT. Science goals for the pho-
high speed encounters with other galax-          One of the limitations in using existing   tometric part of the survey include:
ies and with the global cluster potential     observations to constrain theoretical         characterizing the absolute rest-frame
(galaxy harassment; e.g. Farouki &            models is that most studies of clusters       ultraviolet (UV) to near infrared (NIR)
Shapiro 1981; Moore et al 1996); hot          at z > 0.3 have concentrated on X-ray         spectral energy distributions (SEDs) of
gas envelopes around galaxies can be          selected samples. This biases the sam-        the galaxies; studying galaxy morpholo-
removed by the hot intra-cluster medi-        ples towards the most massive and the         gy as a function of SED; measuring the
um, eliminating the reservoir of gas          densest systems. In addition, the             cluster luminosity functions as a func-


                                                                                                                                   19
tion of redshift and of cluster properties;   scopes is ideally suited for such a proj-     imaging is complete. Most of the data
estimating cluster masses through             ect, which requires optical and NIR im-       were taken under excellent conditions
gravitational lensing; and characterising     agers with excellent image quality and        with almost all combined images having
cluster structure. In practice, this invol-   relatively wide fields, as well as an effi-   <1.0 FWHM seeing. In Figure 1 we
ves deep, high resolution imaging of a        cient multi-object spectrograph mount-        show optical images for four of our clus-
large enough cluster sample to span the       ed on an 8-meter class telescope.             ters. I-band selected catalogues with
(large) expected variance in cluster                                                        multi-band photometry were then con-
properties, the use of bulge-disc de-         Survey Description and Progress               structed using the SExtractor software
composition software to quantify galaxy                                                     (Bertin & Arnouts 1996). The optical
morphology and of photometric red-               To ensure the most efficient use of        and NIR imaging, including the con-
shifts to reject non-members, and the         telescope time, successive refinement         struction of the catalogues, will be de-
careful analysis of faint image shapes to     steps were taken to arrive at a robust        scribed in upcoming papers (White et
measure the gravitational shear.              cluster sample. An original set of 30         al., in preparation; Aragón-Salamanca
   Our follow-up spectroscopy targets a       cluster candidates, 15 with estimated         et al., in preparation).
second set of science goals: measuring        redshifts z ~ 0.5 and 15 with z ~ 0.8,           An initial phase of spectroscopy con-
the stellar and dynamical masses of           was drawn from the optically selected         sisted of a relatively short exposure of a
cluster galaxies; characterizing their        Las Campanas Distant Cluster Survey           single mask in each field to confirm the
chemical abundances, star formation           (LCDCS; Gonzalez et. al. 2001). Given         presence of a true cluster in the expect-
rates (SFRs) dust contents, and star          that the spurious candidate rate in the       ed redshift range. This resulted in the
formation histories (SFHs); comparing         LCDS can be as high as 50% by z ~ 0.8,        elimination of one high-redshift candi-
these with the properties of field galax-     we used four nights on VLT/FORS2 to           date that appeared to be a superposi-
ies at the same redshift; and studying        obtain two-colour images of each field        tion of several weak groups. We then
the dynamical structure of the clusters.      to confirm the presence of a galaxy           began taking longer exposures of 3 or 4
These require high quality spectra for        overdensity with the expected elliptical-     masks per cluster with the aim of ob-
many member galaxies in each cluster          like colours. We then chose the 10 best       taining high quality spectra for ~50
and with well understood sampling and         cluster candidates at each estimated          members in each cluster. As of April
completeness statistics. Only with a          redshift for deeper imaging, followed by      2003 we have observed for 19 of our to-
dataset of this quality is a realistic con-   spectroscopy. These 20 clusters were          tal allocated 22 nights (the eight nights
frontation with theoretical models possi-     observed at the VLT in BVI for the z ~        of data from Spring 2002 are fully re-
ble. Our consortium has already carried       0.5 candidates and VRI for the z ~ 0.8        duced), confirming that all extensively
out suites of high resolution simulations     candidates. In addition, 20 nights of         observed clusters are indeed real. Our
of the formation of clusters and cluster      NIR observations were scheduled at the        final sample will have 7 clusters with
galaxies which can be used to investi-        New Technology Telescope (NTT) using          true redshifts in the range 0.6 ≤ z ≤ 0.8.
gate whether the physical processes           the SOFI NIR camera. This time was            We now have 1240 redshifts for our
outlined above can, in some combina-          used to get Ks-band data for the z ~ 0.5      high redshift clusters, and 554 for our
tion, account for the properties we ob-       candidates and JKs for the z ~ 0.8 can-       low redshift clusters. We project, given
serve for galaxies in our EDisCS sample.      didates. At the present time, all of the      our performance for the first eight
   ESO’s suite of instruments and tele-       optical and all but one night of the NIR      nights, that we now have at least 380




                                                                                            Figure 1: 3-colour images with overlaid weak
                                                                                            lensing mass maps for four of the clusters in
                                                                                            the EDisCS sample. The top two images,
                                                                                            cl1040-1155 on the left and cl1216-1201 on
                                                                                            the right, are from the high-redshift sample
                                                                                            and were imaged in I, R, and V. The bottom
                                                                                            two images, cl1232-1250 on the left and
                                                                                            cl1411-1148 on the right, are from the inter-
                                                                                            mediate-redshift sample and were imaged in
                                                                                            I, V, and B. The yellow arrow in each frame
                                                                                            indicates the location of the BCG. The weak
                                                                                            lensing mass maps are normalized to have
                                                                                            zero mean surface density at the edge of the
                                                                                            images, with the solid contours indicating
                                                                                            positive density, the dotted contour zero den-
                                                                                            sity, and the dashed contours negative den-
                                                                                            sity. Each contour represents a change in
                                                                                            surface mass density of about 10 8 (h70)-1 M /
                                                                                            kpc 2 in an Ωm = 0.3, Λ = 0.7 cosmology. All
                                                                                            of these clusters have been spectroscopical-
                                                                                            ly confirmed with many members, but some
                                                                                            of them show no associated peak in their
                                                                                            weak lensing mass distribution, demonstrat-
                                                                                            ing the diversity of the relation between light
                                                                                            and mass in our cluster sample. Figure pre-
                                                                                            pared by Douglas Clowe.


20
cluster members for the high redshift                                                                               Figure 2: The mean
fields and at least 200 cluster members                                                                             rest-frame bJ-band
for the intermediate redshift fields. After                                                                         galaxy luminosity
the remaining three nights of our allot-                                                                            function for all of our
ted spectroscopy, we should reach final                                                                             z > 0.6 clusters (solid
numbers of 1290/410 at high redshift                                                                                points) and for all of
and 1000/350 at intermediate redshift.                                                                              our z < 0.6 clusters
The spectroscopic data will be present-                                                                             (open points). The
ed in Halliday et al. (in preparation).                                                                             blue solid line is the
   At the present time we already have                                                                              best fit Schechter
an impressive data set, with extensive                                                                              function to the inter-
photometry over a long baseline in                                                                                  mediate redshift sam-
wavelength, a set of 19 fully confirmed                                                                             ple with α fixed at the
clusters at 0.4 < z < 0.8 with a range in                                                                           local value of –1.28.
cluster richness, and fully reduced                                                                                 The red dotted line is
spectroscopy of about 920 galaxies                                                                                  the best fit to the high
(from our spectroscopy in 2002). We                                                                                 redshift sample, also
are, however, still far from being spec-                                                                            with α = –1.28. The
troscopically complete even at bright                                                                               quoted brightening is
magnitudes. We remove non-members                                                                                   with respect to the
from our photometric samples in two                                                                                 2dF cluster luminosity
steps, first by using photometric red-                                                                              function. Figure pre-
shifts calculated with two independent                                                                              pared by Gregory
codes (Rudnick et al. 2001; Hyperz -                                                                                Rudnick.
Bolzonella, Miralles, & Pelló 2000); then
through statistical subtraction of the re-
maining background within a physical
projected radius, rclust = 0.75 (h70)-1
Mpc, using the observed population              newly accreted galaxies and the original       systematically fainter than those al-
density at larger clustercentric distance.      cluster members may also have their            ready present in clusters at high z.
Our photometric redshifts zphot are quite       luminosities altered by merging since
accurate, with 〈 zspec – zphot 〉 =            z = 1. Thus, quite detailed modelling is       The Colour-Magnitude Relation
0.06–0.08 for both the z ~ 0.5 and z ~          needed in order to interpret the evolu-        and Galaxy Morphology
0.8 clusters. Using our photometric red-        tion of cluster LFs.
shifts we reject ~60% of the field galax-          Observations of many local clusters             One powerful characterization of the
ies above the spectroscopic limit and           from 2dF Galaxy Redshift Survey                galaxy population is the joint luminosity-
75–80% of the field galaxies brighter           (2dFGRS) have shown that the LF of             morphology-colour distribution. Different
than I = 25, while retaining ~90% of all        cluster galaxies is remarkably similar for     morphological components are thought
confirmed cluster members, independ-            clusters with many different properties        to have different formation mechanisms
ent of rest-frame colour. The subse-            (De Propris et al. 2002). We use this          and the colour of a galaxy results from a
quent statistical subtraction removes           large local sample as a zero-point for         combination of its dust content, its SFH,
~50% of the remaining galaxies. The             studying evolution in our own dataset.         and its metallicity. Most clusters in the
performance of these techniques will be         Using the observed SED of each                 local universe have a dominant popula-
evaluated in detail in Pelló et al. (in         galaxy, normalized to its total I-band         tion of red galaxies which appear uni-
preparation).                                   flux, and the spectroscopic redshift of        formly old. These “red sequence” galax-
                                                the cluster in which it resides, we derive     ies are spheroid-dominated, but many of
The Cluster Luminosity Function                 the rest-frame bJ luminosity. We then          them also have a significant red disc.
and its Evolution                               use our cleaned cluster galaxy samples         These may be the transformed remnants
                                                to construct a LF for each cluster. To         of infalling spirals. There is also a small
   One important observational charac-          obtain a mean cluster LF in each red-          population of blue galaxies in clusters,
teristic of a galaxy population is its lu-      shift bin, we stack our clusters. We split     whose fractional contribution to the clus-
minosity function (LF), which describes         our sample at z = 0.6 and plot the mean        ter light increases with increasing red-
the galaxy abundance as a function of           high and intermediate redshift LFs in          shift (the so-called “Butcher-Oemler ef-
absolute magnitude. Evolution of the            Figure 2. We determine the brightening         fect”) and whose low redshift descen-
LF encodes how the luminosity distribu-         of our LFs with respect to the local           dants are uncertain.
tion of a galaxy population evolves as a        mean cluster LF from 2dF by fitting with           To study how galaxies are affected by
result of star formation, of stellar aging,     a Schechter function keeping α fixed at        the environments in which they reside,
of obscuration, and of galaxy merging.          the 2dF value of –1.28 and marginali-          it is necessary not only to go backwards
Observations of the structure and kine-         sing over the normalization. This re-          in time, but also to probe a range of en-
matics of cluster ellipticals show that         sults in derived brightenings of ∆MbJ =        vironments at each epoch. It is in this
their stellar mass-to-light ratios have in-     –1.05 ± 0.17 at 〈z〉 ≈ 0.5 and ∆MbJ =           area where EDisCS excels. Using our
creased by about a factor of 2.5 in the         –1.21 ± 0.14 at 〈z〉 ≈ 0.75. This can be        “cleaned” cluster samples we can con-
B-band since z = 1, presumably a result         compared to the brightening predicted          struct optical/NIR colour-magnitude dia-
of the aging of their stars. For mixed          by changing M/L values of ellipticals          grams with galaxies classified by mor-
populations, however, the fading may            (van Dokkum & Stanford, 2003), ∆MbJ =          phology. Examples are shown in Figure
be different because of dust, star for-         –0.57 ± 0.05 at z = 0.5 and ∆MbJ =             3. Immediately obvious is the large vari-
mation, and differential age effects. In        –0.86 ± 0.08 at z = 0.75. It is interesting    ation in the red sequence strength. The
addition, it is important to realise that al-   that we see a fading of the LF which ap-       clusters with a strong red sequence still
though the galaxies which populate              pears larger than expected just from the       have significant numbers of blue galax-
z = 0 clusters do include those which           aging of stars in early-type galaxies. It is   ies, however, although the most lumi-
populate z = 1 clusters, the majority           unclear whether this is due to the inclu-      nous galaxies are almost always red.
would probably be considered “field”            sion of later types in our sample, or to       These blue galaxies reflect the Butcher-
objects at the higher redshift. Both the        the fact that recently added galaxies are      Oemler effect, and we see its cluster-to-

                                                                                                                                        21
Figure 3: Colour-Magnitude morphology diagrams for six
of our intermediate and high redshift clusters. For each
cluster, the colour coding of the points indicates bulge-to-
total ratio. Blue triangles are galaxies with B/T < 0.3,
green plus marks are those with 0.3 ≤ B/T < 0.6, and the
red circles are those with B/T > 0.6. Note the large clus-
ter-to-cluster variation in red sequence strength as well
as the large and variable number of disc-dominated
galaxies which lie on the red sequence. Figure prepared
by Luc Simard.


cluster variation clearly. Another strik-
ing trend is for the relative strength of
the red sequence to decrease with in-
creasing redshift, along with the ratio of
red to blue galaxies at the bright end.
Our spectroscopy will show whether
these bright blue galaxies are still ac-
tively forming stars or if they are “post-
starburst” systems, devoid of current
star formation. Either way, these blue
galaxies must redden with time so that,
by lower redshift, the galaxy popula-
tions in these clusters resemble those
seen in the local universe.
   The excellent quality of our deep VLT
images makes it possible to undertake             are shown in Figure 3, where the differ-     starburst.
detailed morphological studies. Using             ent points correspond to different B/T          Even with the high quality of our
the GIM2D code we perform bulge-disc              values. At all redshifts, the blue galax-    FORS2 data, detailed morphological
decompositions for all galaxies by fitting        ies are predominantly disc-dominated.        classification at z ~ 0.6–0.8 is difficult,
seeing-convolved models directly to the           The red sequence, however, shows a           especially for structural parameters of
2D images. Extensive Monte Carlo                  large number of disc-dominated galax-        the bulge. To improve the quality of our
simulations (e.g., Simard et al. 2002)            ies, even in some of our richest clusters.   morphological classification at high red-
have allowed us to assess where the               In a few clusters, the disc-dominated        shift, we have obtained 80 orbits of
estimated morphological parameters                galaxies even dominate the red se-           Hubble Space Telescope (HST) F814W
can be trusted and we should robustly             quence. What are these galaxies? At          data using the Advanced Camera for
determine the bulge-to-total ratios (B/T)         the bright end, our spectroscopy should      Surveys (ACS) for 10 of our higher red-
and disc scale lengths for the brighter           tell us whether they are dominated by        shift clusters. These data are comprised
galaxies in all our clusters. First results       an old stellar population or by a dusty      of four one-orbit tiles that cover the




                                                                                                                Figure 4: A 5-orbit F814W
                                                                                                                image of the cluster
                                                                                                                cl1037-1243 (z = 0.580)
                                                                                                                taken with the Advanced
                                                                                                                Camera for Surveys
                                                                                                                (ACS) on board the
                                                                                                                Hubble Space Telescope
                                                                                                                (HST). This is one of our
                                                                                                                lowest redshift candidates
                                                                                                                imaged with ACS and
                                                                                                                therefore demonstrates
                                                                                                                the maximum image detail
                                                                                                                which we will obtain. The
                                                                                                                high spatial resolution af-
                                                                                                                forded by these images
                                                                                                                allows us to measure
                                                                                                                bulge scale lengths and
                                                                                                                bulge ellipticities for our
                                                                                                                highest redshift clusters,
                                                                                                                as well as to see small-
                                                                                                                scale structure in many
                                                                                                                galaxies. By using the
                                                                                                                ground-based and HST
                                                                                                                data to constrain the outer
                                                                                                                and inner regions respec-
                                                                                                                tively, we will be able to
                                                                                                                build a detailed picture of
                                                                                                                galaxy morphology in our
                                                                                                                highest redshift clusters.
                                                                                                                Figure prepared by
                                                                                                                Vandana Desai.


22
Figure 5: Stacked ra-                                                                        ulations. In Figure 5 we show the
dial profile for four                                                                        stacked density profile from four clus-
clusters with 〈 z 〉 =                                                                        ters with 〈z〉 = 0.75. Although the indi-
0.75. The black line                                                                         vidual cluster profiles can be quite
counts all retained                                                                          noisy, we clearly detect the mean clus-
galaxies with I < 24,                                                                        ter profile out to 1.5 Mpc.
while the red line                                                                              Our study of cluster structure will not,
counts galaxies                                                                              however, be limited to radial profiles.
rejected using photo-                                                                        Using our suite of high-resolution simu-
metric redshifts.                                                                            lations of cluster and cluster galaxy for-
Note that the rejected                                                                       mation, we can compare models and
galaxies show no                                                                             observations statistically in the full,
concentration to the                                                                         three-dimensional space of observ-
cluster centre (the                                                                          ables (projected position on the sky +
residual non-flatness                                                                        radial velocity). In Figure 6 we compare
is caused by large-                                                                          the projected galaxy density distribution
scale structure unas-                                                                        in two observed clusters with simula-
sociated with the                                                                            tions. All density maps were similarly
clusters) while the                                                                          constructed by smoothing the discrete
mean cluster profile                                                                         galaxy distribution with an adaptive ker-
is detected                                                                                  nel. The input catalogues correspond to
significantly to 1.5                                                                         a magnitude-limited sample, and, in the
Mpc. Figure prepared                                                                         observational case, contain only those
by Gabriella De                                                                              galaxies which survived our photomet-
Lucia.                                                                                       ric redshift cut. It is obvious from these
                                                                                             plots that the detail of the simulations
                                                                                             now matches that of the observations,
same field of view as the deep VLT im-           Cluster Structure                           allowing us to compare the two directly
ages, with an additional four orbit cen-                                                     using such “mock” catalogues.
tral exposure.                                      In addition to studying the galaxy
   A reduced image of the centre of one          populations within our clusters, our        Weak Lensing
of the lowest redshift clusters with HST         large dataset also allows us to study the
imaging, the cluster cl1037-1243, (z =           structure of the clusters themselves. To       The depth and image quality of our
0.58) is shown in Figure 4. This image,          mitigate cluster-to-cluster variations we   VLT imaging is so high that we can de-
which comprises five orbits of exposure          stack the clusters in a given redshift      tect and measure the shapes of many
time, already illustrates the wealth of          range and calculate their mean radial       faint background galaxies lying behind
structure visible, including spiral struc-       profile. Such an average profile can        our clusters. Gravitational lensing ef-
ture and bars. The apparent lack of              meaningfully be compared to a similar-      fects due to the matter within the clus-
bright galaxies with elliptical morpholo-        ly stacked profile of simulated clusters    ters distort these background images
gy is also quite striking. With these            to evaluate whether the physical pro-       causing a weak but measurable ten-
data, we will be able to derive bulge            cesses which influence galaxy proper-       dency for the principal axes of nearby
scale lengths and bulge ellipticities            ties as a function of clustercentric dis-   images to align. Measurements of this
even for our highest redshift clusters.          tance are correctly modelled in the sim-    effect across an image can be inverted




Figure 6: Projected galaxy density maps
smoothed using an adaptive kernel tech-
nique. The bottom right panel shows our
highest redshift cluster cl1216-1201 (z =
0.795) and the top right panel shows the
cluster cl1018-1211 (z = 0.472). All cluster
members at I < 25 are used. In both clus-
ters, many non-members have been exclud-
ed based on photometric redshifts. The pan-
els on the left show projections of two of our
high resolution simulations at similar red-
shifts to the observed clusters. The galaxies
in the simulations are selected over the
same projected area, accepting only objects
within ± 2000 km/s from the brightest cluster
galaxy and applying the same I-band mag-
nitude limit as in the observations. Figure
prepared by Gabriella De Lucia.

                                                                                                                                    23
to obtain a smoothed map of the pro-
jected total mass distribution. This can
be compared with the projected distri-
bution of cluster light and with the clus-
ter mass inferred using the Virial
Theorem and the observed motions of
galaxies within the cluster. The preci-
sion of such mass estimates from grav-
itational lensing can be enhanced by
using photometric redshifts or colour
cuts to isolate galaxies which lie behind
the cluster. In Figure 1 we show mass
surface density contours derived from a
weak lensing analysis overlaid on opti-
cal images of four of our clusters. At
each redshift we show two clusters,
both spectroscopically confirmed to
have many members, but only one of
which shows a clear lensing signal.
These results demonstrate yet again
the diversity of our sample, highlighting
the need for large datasets to correctly
characterize the cluster population.
When our spectroscopy is fully reduced
we will be able to compare the equiva-
lent “velocity dispersion” derived from
lensing to that measured from the
galaxy velocities, allowing us to check if
the clusters are in a relaxed dynamical
state. Deviations from such a state are
to be expected, given the evident
asymmetry of many of our clusters.
Comparison with our simulations will
check whether deviations from a re-
laxed state are at the theoretically pre-
dicted level.

Spectroscopic Science

   The EDisCS project is also distin-
guished by the abundance of high qual-
ity spectroscopy it is assembling. With
these data we will explore in detail the
physical characteristics of the ~800         Figure 7: Measures of velocity width for two galaxies in cl1216-1201 at z = 0.795. The dark
cluster members, together with a             line is the galaxy spectrum with the continuum removed. The red line is the best fit stellar
greater number of field galaxies. As         template convolved with the instrumental resolution and a Gaussian velocity dispersion.
shown in Figure 7, our data are good         Using our spectra, we are able to obtain precise velocity dispersion measurements from ab-
enough to measure the internal kine-         sorption lines down to I ~ 21.5. The instrumental resolution is approx 110 km/s. Figure pre-
matics of galaxies down to at least I =      pared by Roberto Saglia.
21.5. With such spectra we will make
field-to-cluster comparisons for funda-
mental plane and Tully-Fisher evolution,
we will determine how the stellar popu-      modelling, we will then be able to build       References
lations in elliptical galaxies evolve with   up a much clearer picture of how galaxy
time, we will identify active galactic nu-   evolution is driven by internal and envi-      Butcher, H. & Oemler, A. 1978, ApJ, 219, 18
clei, star-forming galaxies and “post-       ronmental processes.                           De Propris et al. 2002, submitted to MNRAS,
starburst” systems, and we will see how         Our programme has shown that the              astro-ph/0212562
the abundance of all such systems            cluster-to-cluster variance in many clus-      Dressler, A. 1980, ApJ, 236, 351
varies with redshift and environment.        ter properties is large. To obtain a pic-      Dressler, A. &Gunn, J. E. 1983, ApJ, 270, 7
Because our spectroscopic selection          ture of the typical clusters as a function     Dubinski, J. 1998, ApJ, 502, 141
                                             of redshift and environment, and to            Farouki, R. & Shapiro, S. L. 1981, ApJ, 243, 32
samples all morphological types, we
                                                                                            Gonzalez, A. H., Zaritsky, D., Dalcanton, J.
can examine the relations between lu-        study the scatter in their properties, it is
                                                                                              J., & Nelson, A. 2001, ApJS, 137, 117
minosity, mass, and size for disc galax-     necessary to study many objects in de-
                                                                                            Gunn, J. E. & Gott, J. R. I. 1972, ApJ, 176, 1
ies and compare these relations in the       tail. Thanks to our large and homoge-          Larson, R. B., Tinsley, B. M., & Caldwell, C.
cluster environment to those in the field    neously selected sample and the high             N. 1980, ApJ, 237, 692
at similar redshift, again providing im-     quality of the imaging and spectroscop-        Moore, B., Katz, N., Lake, G., Dressler, A., &
portant constraints for models of galaxy     ic data provided by ESO facilities, a            Oemler, A. 1996, Nature, 379, 613
evolution. In combination with our pho-      comparison of the EDisCS dataset to            Simard, L. et al. 2002, ApJS, 142, 1
tometric SEDs, the spectral range of our     nearby large cluster samples and to de-        Springel, V., White, S. D. M., Tormen, G., &
observations will allow us to character-     tailed theoretical models will substan-          Kauffmann, G. 2001, MNRAS, 328, 726
ize the stellar populations, SFRs, heavy     tially improve our understanding of how        van Dokkum, P. G. & Stanford, S. A. 2003,
element abundances, and SFHs of our          galaxies have evolved since the uni-             ApJ, 585, 78
galaxies. In combination with detailed       verse was half its present age.                White, S. D. M. 1976, MNRAS, 174, 19


24
SPY — The ESO Supernovae Type Ia
Progenitor Survey
R.   NAPIWOTZKI1, N. CHRISTLIEB 2, H. DRECHSEL1, H.-J. HAGEN 2, U. HEBER1,
D.   HOMEIER4, C. KARL1, D. KOESTER3, B. LEIBUNDGUT 5, T.R. MARSH 6,
S.   MOEHLER 3, G. NELEMANS7, E.-M. PAULI1, D. REIMERS2, A. RENZINI5,
L.   YUNGELSON 8
1
  Dr. Remeis-Sternwarte, Universität Erlangen-Nürnberg, Bamberg, Germany; 2Hamburger Sternwarte,
Hamburg, Germany; 3Institut für Theoretische Physik und Astrophysik, Universität Kiel, Germany; 4Department of
Physics & Astronomy, University of Georgia, USA; 5European Southern Observatory, Garching, Germany;
6
 Department of Physics & Astronomy, University of Southampton, UK; 7Institute of Astronomy, Cambridge, UK;
8
 Institute of Astronomy of the Russian Academy of Sciences, Moscow, Russia
Supernovae and their                             2000). SN Ia are observed in all types of      Since type Ia supernovae were identi-
progenitors                                      galaxies, including elliptical galaxies        fied as excellent distance indicators for
                                                 containing only old stellar populations.       cosmology and have provided indica-
   Supernovae (SNe) mark the violent             The light curves of SN Ia are dominated        tions of cosmic acceleration, it is ex-
termination of a star’s life in an explo-        by the decay of the radioactive material       tremely important to have a better un-
sion. They are classified according to           synthesized in the explosion (mainly           derstanding of their explosions and the
their light curve as type I or II, with the      nickel). The 56Ni isotope sits at the top      systems that lead up to them. While it is
type I SNe producing very similar light          of a decay chain leading to 56Co (half-        possible to test the quality of the dis-
curves, while the SNe type II are more           life 6.1 days) and to stable 56Fe (half-life   tance indicator in the nearby universe
diverse. Spectroscopic observations re-          77 days). The rapid evolution of SN Ia         by checking the linear Hubble expan-
veal the presence of hydrogen in SNe             light curves indicates that the precur-        sion, one has to rely on the accuracy of
type II, while no hydrogen lines are de-         sors of these supernovae must be com-          the distance indicator to go beyond the
tectable in SNe type I. According to             pact objects of small mass with very lit-      linear Hubble flow and probe the red-
their spectral appearance the type I             tle mass holding back the gamma-rays           shift regime, where the cosmological
class can be further subdivided into Ia,         produced by the radioactive decay. The         models differ in their predictions. At this
Ib, and Ic.                                      only candidate, which can fulfill the ob-      point, other signatures of the reliability
   SNe type II and Ib,c are observed             servational constraints, is the thermo-        of the distance indicator have to be se-
only in spiral galaxies and irregular            nuclear explosion of a white dwarf.            cured. With lookback times of about half
galaxies containing young stellar popu-
lations. This indicates that their progen-
itors are short-lived massive stars
(masses above 8 M ). Indeed, the oc-
currence of SN explosions and the for-
mation of a neutron star remnant at the
end of the nuclear lifetime of a massive
star are now relatively well understood
processes.
   However, the question of SN Ia pro-
genitors is not yet settled (e.g. Livio


Figure 1: Possible evolutionary channels for
the formation of a SN Ia progenitor via the
double degenerate (DD) and the single de-
generate (SD) scenarios. In both scenarios
the evolution starts with a binary of two main
sequence (MS) stars. The more massive
star becomes a red giant and its envelope is
ejected in a common envelope event. In the
DD scenario the second MS star evolves to
a red giant with a second common envelope
event and the formation of a close binary of
two white dwarfs (WD). If the DD system is
close enough and massive enough, gravita-
tional wave radiation will cause it to merge
and explode as a SN Ia. In the two variants
of the SD scenario the secondary fills its
Roche lobe while i) close to the main se-
quence or as red giant (RG) or ii) as a He-
star after another common envelope phase.
Mass is transferred onto the WD star and in-
creases the WD mass until the
Chandrasekhar limit is reached. Note that
the SD scenarios predict the survival of the
companion star.

                                                                                                                                       25
                                                                                                         Figure 2: Distribution of all
                                                                                                         known white dwarfs south
                                                                                                         of δ = +25° and brighter
                                                                                                         than V = 16.5. Red
                                                                                                         squares indicate white
                                                                                                         dwarfs with two spectra
                                                                                                         taken by SPY.
                                                                                                         A second spectrum
                                                                                                         remains to be collected for
                                                                                                         the green triangles, while
                                                                                                         the black dots are the re-
                                                                                                         maining objects without a
                                                                                                         SPY observation. The yel-
                                                                                                         low band indicates the po-
                                                                                                         sition of the Galactic disk
                                                                                                         (|b| < 20°).




the current age of the universe, one has      no physical process is known which          quence star, a (super)giant, or a helium
to make sure that evolution of the dis-       leads to such conditions in a single        star, as mass donor and the double de-
tance indicator is not mimicking a cos-       white dwarf, a companion star has to        generate (DD) channel where the com-
mological effect. To do this reliably one     help. This general picture of binary        panion is another white dwarf. Close
has to try to understand the distance in-     white dwarfs as the progenitor stars for    DDs radiate gravitational waves, which
dicator in as many aspects as possible.       type Ia supernovae is the most com-         results in a shrinking orbit due to the
One of the shortcomings of type Ia su-        monly held view today.                      loss of energy and angular momentum.
pernovae is our ignorance of the pro-            The growth of a white dwarf to           If the initial separation is close enough
genitor systems and the exact explo-          Chandrasekhar mass is a long-standing       (orbital periods below 10 h), a DD sys-
sion mechanism. By identifying these          problem of observational astrophysics.      tem could merge within a Hubble time,
progenitors we should be able to con-         Several channels have been identified       and if the combined mass exceeds the
strain possible evolutionary effects on       as possibly yielding such a critical mass   Chandrasekhar limit the DD would qual-
the cosmological result.                      (Fig. 1). They can broadly be grouped       ify as a potential SN Ia progenitor.
   While the cosmic microwave back-           into two classes (e.g. Livio 2000). The        The double degenerate scenario for
ground experiments have provided a            single degenerate (SD) channel in           the progenitors was proposed many
phenomenal accuracy of the integrated         which the white dwarf is accompanied        years ago. So far, no SN Ia progenitor
cosmological parameters, they cannot          by a regular star, either a main se-        has been identified, which is not really
provide the more detailed measure-
ments to explore the expansion history
of the universe, i.e. the equation of state
parameter. Only distance indicators,
like type Ia supernovae, can yield this
information. But the systematics of
these derivations have to be assessed
as precisely as possible. The knowl-
edge of the precursor state and the
physics of the transformation to the su-
pernova are hence vital ingredients for
our understanding of cosmology.
   Most stars (i.e. all stars with a mass
below about 8 solar masses) will end
their lives as white dwarfs. These are                                                                          Figure 3: UVES
small cooling bodies consisting mainly                                                                          spectrum of the DA
of carbon and oxygen with thin layers of                                                                        white dwarf WD
hydrogen and/or helium on top, sup-                                                                             1026+023. The up-
ported by degenerate electron gas.                                                                              per three panels
They will cool for billions of years and                                                                        correspond to the
disappear as small cold clumps into the                                                                         blue channel and to
cosmic background without signs of                                                                              both parts of the red
their once glorious lives. Some white                                                                           channel covered by
dwarfs will, however, destroy them-                                                                             different CCDs. The
selves in a gigantic thermonuclear ex-                                                                          spectra were
plosion. To do so, they have to be                                                                              smoothed to a reso-
forced into a density and temperature                                                                           lution of 1 Å.
regime, where carbon and oxygen burn                                                                            Two reduction arti-
explosively and disrupt the star. Above                                                                         facts are indicated
the Chandrasekhar mass (1.4 M ) the                                                                             by asterisks.
electron degeneracy can no longer sup-                                                                          The lower panel
port white dwarfs. At this point the white                                                                      shows the unbinned
dwarf either has to collapse to a neutron                                                                       spectra of the Hα
star or explode as a supernova. Since                                                                           and Hβ line cores.

26
surprising considering the rareness of                                                                         Figure 4: Three single-
SNe Ia and the small volume that can                                                                           lined RV variable DDs
be surveyed for white dwarfs. The or-                                                                          from our VLT survey. The
bital velocity of white dwarfs in potential                                                                    vertical line marks the
SN Ia progenitor systems must be large                                                                         rest wavelength of Hα.
(>150 km/s) making radial velocity (RV)                                                                        The spectra are slightly
surveys of white dwarfs the most prom-                                                                         rebinned (0.1 Å) without
ising detection method. Several sys-                                                                           degrading the resolution.
tematic RV searches for DDs were un-
dertaken starting in the mid 1980’s.
Before 2001, combining all the surveys,
    200 white dwarfs were checked for
RV variations with sufficient accuracy
yielding 18 DDs with periods P < 6.3 d
(Marsh 2000 and references therein).
None of the 18 systems seems massive
enough to qualify as a SN Ia precursor.
This is not surprising, as theoretical
simulations suggest that only a few per-
cent of all DDs are potential SN Ia pro-
genitors (Iben, Tutukov & Yungelson
1997; Nelemans et al. 2001). It is obvi-
ous that larger samples are needed for
statistically significant tests.
   The surveys mentioned above were
performed with 3–4-m class telescopes.
A significant extension of the sample
size without the use of larger telescopes
would be difficult due to the limited num-
ber of bright white dwarfs. This situation
changed after the ESO VLT became
available. In order to perform a defini-
tive test of the DD scenario we have
embarked on a large spectroscopic sur-          the detection of galaxies and quasars         spectra is in most cases very good; es-
vey of more than 1000 white dwarfs us-          and restricted to high Galactic latitudes.    pecially the removal of the interorder
ing the UVES spectrograph at the UT2               Spectra were taken with the UV-            sensitivity variation and merging of the
telescope (Kueyen) of VLT to search for         Visual Echelle Spectrograph (UVES) of         orders works very well. Sometimes the
RV variable white dwarfs (ESO SN Ia             the UT2 telescope (Kueyen) of the ESO         reduction pipeline produces artifacts of
Progenitor surveY – SPY). SPY will              VLT. UVES is a high resolution Echelle        varying strength, e.g. a quasiperiodic
overcome the main limitation of all ef-         spectrograph, which can reach a reso-         pattern in the red region similar in ap-
forts so far to detect DDs that are plau-       lution of 110,000 in the red region with      pearance to a fringing pattern. In a few
sible SN Ia precursors: the samples of          a narrow slit. Our instrument set-up          cases either the blue or the red part of
surveyed objects were too small.                (Dichroic 1, central wavelengths 3900         the spectrum has extremely strong arti-
                                                Å and 5640 Å) uses UVES in a dichroic         facts of unknown origin. This pipeline
The survey                                      mode. Nearly complete spectral cover-         reduction was extremely useful for a
                                                age from 3200 Å to 6650 Å with only two       fast selection of RV variable DDs for fol-
   As outlined above, we need a very            roughly 80 Å wide gaps at 4580 Å and          low-up observations (described below).
large input sample of white dwarfs,             5640 Å is achieved.                           In the meantime we have produced a
which are bright enough (B 16.5) to                Our programme was implemented as           semi-automatic set of procedures for
take high-resolution spectra with a suf-        a large programme in service mode. It         the reduction of our UVES spectra. A re-
ficiently high signal-to-noise ratio. The       takes advantage of those observing            reduction of the survey data is already
most complete catalogue of spectro-             conditions, which are not usable by           completed and yielded a large set of
scopically confirmed white dwarfs is the        most other programmes (moon, bad              good quality white dwarf spectra.
actual version of the McCook & Sion             seeing, clouds) and keeps the VLT busy            As an example of the quality achiev-
(1999) catalogue. However, it contains          when other programmes are not feasi-          able the spectrum of a hydrogen-rich
“only” 918 white dwarfs brighter than           ble. A wide slit (2.1 ) is used to minimize   DA white dwarf is shown in Fig. 3. A
B = 16.5 south of δ = +25°. Since we            slit losses and a 2 x 2 binning is applied    characteristic feature of white dwarfs
needed a larger input sample, we                to the CCDs to reduce read out noise.         are the very broad spectral lines caused
added more objects from recent sur-             Our wide slit reduces the spectral reso-      by the high densities in their atmos-
veys: the Hamburg-ESO survey (HES),             lution to R = 18,500 (0.36 Å at Hα) or        pheres. Obviously, broad lines are very
the Hamburg-Quasar survey (HQS), the            better, if seeing discs were smaller than     ill-suited for RV measurements. Howe-
Montreal-Cambridge-Tololo survey (MCT),         the slit width. Depending on the bright-      ver, deviations from local thermal equi-
and the Edinburgh-Cape survey (EC). A           ness of the objects, exposure times be-       librium (LTE) produce sharp NLTE
map of all known white dwarfs (ob-              tween 5 min and 10 min were chosen.           cores of the Hα lines in the atmos-
served and unobserved by SPY) fulfill-          The S/N per binned pixel (0.03 Å) of the      pheres of hydrogen-rich DA white
ing our criteria is shown in Fig. 2. A strik-   extracted spectrum is usually 15 or           dwarfs (Fig. 3), which allow accurate
ing feature is a lack of white dwarfs in        higher. Due to the nature of the project,     RV measurements. This feature is not
the Galactic plane. This cannot be ex-          two spectra at different, “random”            present in non-DA white dwarfs (spec-
plained by interstellar extinction, be-         epochs separated by at least one day          tral types DB, DO) with hydrogen-poor
cause bright white dwarfs are nearby            are observed.                                 atmospheres, but the use of several he-
objects. However, all major surveys dur-           ESO provides a data reduction              lium-lines enables us to reach a similar
ing the last decades (including the sur-        pipeline for UVES, based on MIDAS             accuracy.
veys mentioned above) were aimed at             procedures. The quality of the reduced            Since SPY produces a large number

                                                                                                                                     27
                                                                                            tions we have detected a very promis-
Figure 5: Mass deter-                                                                       ing potential SN Ia precursor candidate.
mination of (single and                                                                     However, some additional observations
binary) DA white                                                                            are necessary to verify our RV curve so-
dwarfs. Temperature                                                                         lution.
and gravity, determined                                                                        Although important information like
from a model                                                                                the periods, which can only be derived
atmosphere analysis of                                                                      from follow-up observations, are pre-
the UVES spectra                                                                            sently lacking for most of the stars, the
(Koester et al., 2001)                                                                      large sample size already allows us to
are compared to cool-                                                                       draw some conclusions. (Note that fun-
ing sequences of white                                                                      damental white dwarf parameters like
dwarfs (Blöcker et al.,                                                                     masses are known from the spectral
1997) for a range of                                                                        analysis described below). One inter-
white dwarf masses.                                                                         esting aspect concerns white dwarfs of
                                                                                            non-DA classes (basically the helium-
                                                                                            rich spectral types DB, DO, and DZ, in
                                                                                            contrast to the hydrogen-rich DAs).
                                                                                            SPY is the first RV survey which per-
                                                                                            forms a systematic investigation of both
                                                                                            classes of white dwarfs: DAs and non-
of spectra, which have to be checked            ondary. Our sample includes many            DAs. Previous surveys were restricted
for RV variations, a fast and reliable al-      short period binaries (some examples        to DA white dwarfs. Our result is that the
gorithm to measure RV shifts is neces-          are discussed in the next section), sev-    binary frequency of the non-DA white
sary. We apply a “cross-correlation”            eral with masses closer to the              dwarfs is equal to the value determined
routine based on a χ2 test (description         Chandrasekhar limit than any system         for the DA population within the statisti-
in Napiwotzki et al. 2001). The RV shift        known before. In addition, we detected      cal accuracy.
is evaluated from the minimum χ2. Error         19 RV variable systems with a cool
margins can be estimated from the χ2            main sequence companion (pre-cata-          Parameters of
statistics as well. One great advantage         clysmic variables; pre-CVs). Some ex-       double degenerates
of our procedure is its flexibility and that    amples of single-lined and double-lined
it can easily be applied to measure RV          DDs are shown in Fig. 4 and 7. Our ob-        Once the binaries in the white dwarf
shifts in stars of different spectral types     servations have already increased the       sample have been revealed, follow-up
(Balmer lines of DA white dwarfs, HeI           DD sample by a factor of seven. After       observations are necessary to deter-
lines of DBs, HeII and metal lines of hot       completion, a final sample of about 150     mine the system parameters of the
DO white dwarfs). We routinely meas-            DDs is expected.                            DDs. We concentrated on candidates
ure RVs with an accuracy of about 2                Follow-up observations of this sam-      with high RV variations, indicating short
km/s, therefore running only a very             ple are mandatory to exploit its full po-   periods, because the probability to find
small risk of missing a merger precur-          tential. Periods and white dwarf param-     potential SN Ia candidates is highest
sor, which have orbital velocities of 150       eters must be determined to find poten-     among these systems. However, let us
km/s or higher.                                 tial SN Ia progenitors among the candi-     note that probably some of the “small
   The large programme was finished at          dates. Good statistics of a large DD        RV” DDs could be short period systems
the end of last semester. A total of 1014       sample will also set stringent con-         (possibly even SN Ia progenitors) with
stars were observed (Fig. 2). This cor-         straints on the evolution of close bina-    low inclination angles and/or un-
responds to 75% of the known white              ries, which will dramatically improve our   favourable phase differences of the
dwarfs accessible by VLT and brighter           understanding of this phase of stellar      SPY observations.
than B =16.5. A second spectrum is still        evolution. During our follow-up observa-      The secondary of most DD systems
lacking for 242 white dwarfs, but time
has been granted to complete these ob-
servations. Currently we could check
772 stars for RV variations, and detect-
ed 121 new DDs, 16 are double-lined
systems (only 6 were known before).
The great advantage of double-lined bi-
naries is that they provide us with a well
determined total mass. Since it is likely
that the SPY sample contains even
more double-lined systems (with a faint
secondary), we will check follow-up ob-
servations of apparently single-lined
systems for the signature of the sec-

Figure 6: Periods (P) and system masses
(Mtotal) determined from follow-up observa-
tions of DDs from SPY. Results for double-
lined systems (black circles) are compared
to previously known systems (green circles).
The other DD systems are single-lined (tri-
angles: WD primaries; diamonds: sdB pri-
maries). The masses of the unseen com-
panions are estimated from the mass func-
tion for the expected average inclination an-
gle (i = 52 °).


28
                                                               spectra of single-lined       tional redshifts can be computed as a
                                                               systems. The RVs of           function of mass. Since the mass ratio
                                                               both white dwarfs can         is given by Eq. 2, only one combination
                                                               be measured, and the          of masses can fulfil both constraints. In
                                                               orbits of both individual     the case of He1414-0828 we derived in-
                                                               components can be de-         dividual masses M1 = 0.55 ± 0.03 M
                                                               termined (Fig. 8). For        and M2 = 0.71 ± 0.03 M . The result for
                                                               our example HE1414-           HE1414-0848 did not depend much
                                                               0848 we derived a peri-       (deviations not larger than 0.01 M ) on
                                                               od of P=12h25m44s and         the particular choice of a mass-radius
                                                               semi-amplitudes K1 =          relation. The sum of both white dwarf
                                                               127 km/s and K2 = 96          masses is M = 1.26 ± 0.06 M . Thus
                                                               km/s. The ratio of veloc-     HE1414-0848 is a massive DD with a
                                                               ity amplitudes is directly    total mass only 10% below the
                                                               related to the mass ratio     Chandrasekhar limit.
                                                               of both components:
                                                                   M2 / M1 = K1 / K2 =          If double-lined systems contain white
                                                               1.28 ± 0.02. (2)              dwarfs of low mass and/or similar mass
                                                                                             the gravitational redshift differences are
                                                                     However, additional     very small and this method cannot be
                                                                  information is needed      used to determine absolute masses.
                                                                  before the absolute        Another method, which works in these
                                                                  masses can be deter-       cases as well, are model atmosphere
                                                                  mined. There exist two     analyses of the spectra to determine the
                                                                  options to achieve this    fundamental parameters effective tem-
                                                                  goal in double-lined       perature and surface gravity, g =
                                                                  DDs. From Fig. 8, it is    GM/R2, of the stars. Because the
                                                                  evident that the “system   HE1414-0848 system is double-lined
                                                                  velocities” derived for    the spectra are a superposition of both
                                                                  components 1 and 2 dif-    individual white dwarf spectra. A direct
                                                                  fer by 14.3 km/s, much     approach would be to disentangle the
                                                                  more than naively ex-      observed spectra by deconvolution
Figure 7: Hα spectra of HE 1414-0848 covering 5 hours during pected from the error           techniques into the spectra of the indi-
one night together with a fit of the line cores. The numbers in- bars. However, this is      vidual components. Then we could
dicate the Julian date of the exposures and the orbital phase φ. easily explained by the     analyse the spectra by fitting synthetic
                                                                  mass dependent gravi-      spectra developed for single-lined white
has already cooled down to invisibility. tational redshift of white dwarfs, z =              dwarfs to the individual line profiles.
These DDs are single-lined spectro- GM/(Rc 2).                                               Such procedures were successfully ap-
scopic binaries (SB1). Our spectroscop-              This offers the opportunity to deter-   plied to main sequence double-lined bi-
ic follow-up observations allow us to de- mine masses of the individual white                naries. However, they have not been
termine the orbit of the primary compo- dwarfs in double-lined DDs. For a given              tested for white dwarfs, for which the
nent (i.e. the period P and the radial ve- mass-radius relation (e.g. from the cool-         wavelength shifts caused by orbital mo-
locity amplitude K1). The mass of the ing sequences plotted in Fig. 5) gravita-              tions are much smaller than the line
primary M1 is known from a model at-
mosphere analysis (Fig. 5). Cons-
traints on the mass of the secondary M2
can be derived from the mass function:
    3   3             2      3
M2 sin i / (M1 + M2) = K1 P/(2πG).           (1)

    For a given inclination angle i the
mass of the secondary can be comput-
ed. However, i is rarely known, but the
result for i = 90° yields a lower mass lim-
it. For a statistical analysis it is useful to
adopt the most probable inclination i =
52°. We have plotted the single-lined
systems with the resulting system mass
in Fig. 6. Note that two binaries have
probably combined masses in excess of
the Chandrasekhar limit. However, the
periods are rather long preventing
merging within a few Hubble times.

   Sometimes spectral features of both
DD components are visible (Fig. 7), i.e.
these are double-lined spectroscopic bi-
naries (SB2). As an example for other
double-lined systems we discuss here
the DA+DA system HE1414-0848
(Napiwotzki et al. 2002). On one hand               Figure 8: Measured RVs as a function of orbital phase and fitted sine curves for HE
the analysis is complicated for double-             1414-0848. Blue circles/red rectangles indicate the less/more massive component.
lined systems, but on the other hand the            Note the difference of the ``systemic velocities'' γ0 between both components caused
spectra contain more information than               by gravitational redshift.


                                                                                                                                    29
widths of the broad Balmer lines.
                                                                                                                      Figure 9: Model
Therefore we choose a different ap-
                                                                                                                      atmosphere fit of the
proach for our analysis of double-lined
                                                                                                                      Balmer series of HE
DD systems. We used the programme
                                                                                                                      1414-0848 with
FITSB2, which performs a spectral
                                                                                                                      FITSB2. This is only a
analysis of both components of double-
                                                                                                                      sample fit. All
lined systems. It is based on a χ2 mini-
                                                                                                                      available spectra,
mization technique using a simplex al-
                                                                                                                      covering different or-
gorithm. The fit is performed on all avail-
                                                                                                                      bital phases, were
able spectra covering different spectral
                                                                                                                      used simultaneously.
phases simultaneously, i.e. all available
spectral information is combined into
the parameter determination procedure.
   The total number of fit parameters
(stellar and orbital) is high. Therefore
we fixed as many parameters as possi-
ble before performing the model atmos-
phere analysis. We have kept the radial
velocities of the individual components
fixed according to the radial velocity
curve. Since the mass ratio is already
accurately determined from the radial
velocity curve we fixed the gravity ratio.
The remaining fit parameters are the ef-
fective temperatures of both compo-
nents and the gravity of the primary.
The gravity of the secondary is adjusted
according to the primary value during
the fitting procedure. The surface gravi-     closer to the Chandrasekhar limit than          time to tackle many longstanding ques-
ties also determine the relative weight       any system known before, greatly im-            tions on a firm statistical basis. Among
of the two model spectra from the ra-         proving the statistics of DDs. We expect        those are the mass distribution of white
dius, obtained from mass-radius rela-         this survey to produce a sample of              dwarfs, the kinematical properties of the
tions. The flux ratio in the V-band is cal-   about 150 DDs.                                  white dwarf population, surface compo-
culated from the actual parameters and           This will allow us not only to find sev-     sitions, luminosity function, rotational
the model fluxes are scaled according-        eral of the long sought potential SN Ia         velocities, and detection of weak mag-
ly. The individual contributions are up-      precursors (if they are DDs), but will          netic fields. A first part of the SPY sam-
dated consistently as part of the itera-      also provide a census of the final bina-        ple was published in a recent paper of
tion procedure.                               ry configurations, hence an important           Koester et al. (2001), covering observa-
   The results for HE1414-0848 are            test for the theory of close binary star        tions of about 200 white dwarfs of spec-
Teff/log g = 8380 K/7.83 and 10900            evolution after mass and angular mo-            tral types DA and DB. For all spin-off op-
K/8.14 for components 1 and 2. A sam-         mentum losses through winds and com-            portunities mentioned above the statis-
ple fit is shown in Fig. 9. The derived log   mon envelope phases, which are very             tics will be dramatically improved by the
g values are in good agreement with the       difficult to model. An empirical calibra-       final white dwarf spectra database. We
values corresponding to the masses de-        tion provides the most promising ap-            are exploiting the SPY sample for two
rived from the RV curves: log g = 7.92        proach. A large sample of binary white          spin-off projects, which take advantage
and 8.16, respectively.                       dwarfs covering a wide range in param-          of the high spectral resolution: the kine-
   We have plotted HE1414-0848 as             eter space is the most important ingre-         matics of white dwarfs (Pauli et al.
well as our other results on double-lined     dient for this task.                            2003) and their rotational velocities. A
systems in Fig. 6. Note that one double-         Our ongoing follow-up observations           more detailed description of ongoing
lined system is probably a SN Ia pro-         already revealed the existence of three         spin-off activity is given in Napiwotzki et
genitor. However, the RV curve of the         short period systems with masses close          al. (2001).
hotter component is very difficult to         to the Chandrasekhar limit, which will
measure causing the large error bars.         merge within 4 Gyrs to two Hubble               References
Observing time with the far-UV satellite      times. Even if it will finally turn out that
FUSE has been allocated, which will           the mass of our most promising SN Ia            Blöcker, T., Herwig, F., Driebe, T., Bramkamp,
enable us to measure more accurate            progenitor candidate system is slightly            H., Schönberner D.1997, in: White dwarfs,
RVs.                                          below the Chandrasekhar limit, our re-             eds. J. Isern, M. Hernanz, E. Garcia-
                                              sults already allow a qualitative evalua-          Berro, Kluwer, Dordrecht, p.57
                                                                                              Iben, I. Jr., Tutukov, A. V., Yungelson, L. R.,
Concluding remarks                            tion of the DD channel. Since the for-             1997, ApJ, 475, 291
                                              mation of a system slightly below               Koester, D., Napiwotzki, R., Christlieb, N., et
   The large programme part of SPY            Chandrasekhar limit is not very different          al., 2001, A&A, 378, 556
has now been completed with some ob-          from the formation of a system above            Livio, M., 2000, in: “Type Ia Supernovae:
servations underway to complete the           this limit, the presence of these three            Theory and Cosmology”, Cambridge Univ.
observations of the white dwarfs with         systems alone provides evidence (al-               Press, p. 33
only one spectrum taken during the sur-       though not final proof) that potential DD       Marsh, T. R., 2000, NewAR, 44, 119
vey. We increased the number of white         progenitors of SN Ia do exist.                  McCook, G. P., Sion, E. M., 1999, ApJS, 121, 1
                                                                                              Napiwotzki, R., Christlieb, N., Drechsel, H.,
dwarfs checked for RV variablity from
                                                                                                 et al. 2001, AN, 322, 201
200 to 1000 and multiplied the number         Spin-off results                                Napiwotzki, R., Koester, K., Nelemans, G., et
of known DDs by a factor of seven (from         SPY produces an immense, unique                  al., 2002, A&A, 386, 957
18 to 139) compared to the results            sample of very high resolution white            Nelemans, G., Yungelson, L. R., Portegies
achieved during the last 20 years. Our        dwarf spectra. This database will have             Zwart, S. F., Verbunt, F., 2001, A&A, 365, 491
sample includes many short period bi-         a large impact on many fields of white          Pauli, E.-M., Napiwotzki, R., Altmann, M. et
naries (Fig. 6), several with masses          dwarf science. It will allow us for the first      al., 2003, A&A, 400, 877


30
Abundances in Globular Cluster Dwarfs
R.G. GRATTON1, P. BONIFACIO 2, A. BRAGAGLIA3, E. CARRETTA1, V. CASTELLANI4,
M. CENTURION2, A. CHIEFFI5, R. CLAUDI1, G. CLEMENTINI3, F. D’ANTONA6,
S. DESIDERA1,7, P. FRANCOIS 8, F. GRUNDAHL9, S. LUCATELLO1,7, P. MOLARO 2,
L. PASQUINI 8, C. SNEDEN10, F. SPITE11, O. STRANIERO12, M. ZOCCALI 8
1
 Osservatorio Astronomico di Padova, INAF, Italy; 2Osservatorio Astronomico di Trieste, INAF, Italy; 3Osservatorio
Astronomico di Bologna, INAF, Italy; 4Dipartimento di Fisica, Università di Pisa, Italy; 5Istituto di Astrofisica
Spaziale, CNR, Italy; 6Osservatorio Astronomico di Roma, INAF, Italy; 7Dipartimento di Astronomia, Università di
Padova, Italy; 8European Southern Observatory; 9Department of Astronomy, University of Aarhus, Denmark;
10
   The University of Texas at Austin, USA; 11Observatoire de Meudon, France; 12Osservatorio Astronomico di
Collurania, INAF, Italy


   Globular Clusters are huge, very
compact aggregates of hundreds of
thousands of stars (see Figure 1).
There are about 150 such systems in
our Galaxy, the closest being about
10,000 light years from us; some of
them are visible with the naked eye (ω
Centauri, 47 Tucanae), and many oth-
ers are spectacular objects visible with
small telescopes.
   Globular Clusters play an important
role in modern astrophysics mainly be-
cause they are the oldest objects in our
Galaxy and in the whole Universe that
we can accurately date. Provided that
their distances are known, ages of
Globular Clusters can in fact be deter-
mined quite precisely from the luminos-
ity of the turn-off stars, that is the stars
that are exhausting Hydrogen at their
centre. The oldest Globular Clusters are
so old that they formed when the
Universe was very young, and very dif-
ferent from what it appears now.
Accurately dating them is then basic to
constraining the early epochs of forma-
tion of our own Galaxy, and even the
age of the Universe. This last is impor-
tant for cosmology: combined with esti-
mates of the Hubble constant, it may tell
us about the presence and nature of the
mysterious dark energy, whose pres-
ence is suggested by the apparent de-
cline of the luminosity of type Ia super-      Figure 1: Image of a typical Globular Cluster (NGC 5024)
novae at high redshifts (Perlmutter et al.
1999), and by the characteristics of the
X-ray emission of galaxy clusters (see         ponents of the thin disc. These               that temporarily cleaned our Galaxy of
the review by Rosati et al. 2002).             “younger” Globular Clusters differ sys-       gas from which stars could form. This
   Observations of external galaxies in-       tematically from the oldest ones: they        strong dynamical interaction may be the
dicate that Globular Clusters form dur-        are more metal rich, and more concen-         site for the formation of the group of
ing epochs of strong dynamical interac-        trated toward the centre of the Galaxy.       “younger” Globular Clusters. Precisely
tions. The lack of young Globular              This second group of clusters is proba-       dating them can help to fix the scenario
Clusters in our Galaxy can then be con-        bly related to the thick disc, and per-       of the early evolution of the Galaxy.
nected to the presence of the thin disc:       haps to the bulge. Comparison between
in fact the thin disc would have been de-      the chemical composition of the thick         Globular Cluster distances
stroyed by strong dynamical interac-           and thin disc stars suggests that there
tions. The oldest components of the thin       was an interval of low star formation be-        Dating Globular Clusters requires
disc formed about 10 Gyr ago. While a          tween these two phases of the history of      knowledge of their distances. Globular
substantial fraction of the Galactic           our Galaxy (Gratton et al. 1996). This        Clusters are too far for direct distance
Globular Clusters seems to be coeval           hiatus in the star formation might be due     estimates using trigonometric parallax-
and extremely old, there is a group of         to the accretion of a gas rich satellite,     es with the presently available instru-
clusters that appears to be slightly           which may have caused the heating of          mentation, although in the next decade
younger (Rosenberg et al. 1999), al-           the pre-existing disc, a burst of star for-   accurate distances will be likely ob-
though still older than the oldest com-        mation, and possibly a galactic wind          tained with GAIA. However, distances

                                                                                                                                  31
Figure 2: Location                                                                           abundances from weak metallic lines. In
in the colour mag-                                                                           principle the method requires extraction
nitude of the stars                                                                          of these parameters for the same field
observed in our                                                                              and cluster stars used to derive dis-
programme in the                                                                             tances, that is, unevolved stars that are
Globular Clusters                                                                            still on the main sequence. However,
NGC6397 and                                                                                  these stars are very faint even in the
NGC6752 (from                                                                                closest Globular Clusters. Slightly
Gratton et al.                                                                               evolved stars near the turn-off can still
2001)                                                                                        be used: these are accessible in the
                                                                                             case of the closest Globular Clusters
                                                                                             using UVES at KUEYEN. If this tech-
                                                                                             nique is used, uncertainties in the dis-
                                                                                             tances are reduced to about 3%, allow-
                                                                                             ing determinations of ages with errors of
                                                                                             only about 1 Gyr. Such an accurate de-
                                                                                             termination allows much more critical
                                                                                             tests for both cosmology and Galaxy
                                                                                             evolution.
                                                                                                UVES at the VLT is particularly suit-
                                                                                             able for a number of reasons: first, it is
                                                                                             a very efficient spectrograph providing
                                                                                             enough spectral resolution and S/N on
                                                                                             faint sources (V~17) such as Turn-Off
                                                                                             stars in Globular Clusters; second, the
                                                                                             wide spectral coverage observable in a
to Globular Clusters can be obtained            On the other side, temperatures and          single exposure allows simultaneous
with various more indirect techniques.       metallicities can be derived, independ-         observation of Hα and of a suitable
In the next few years, high precision dis-   ently of concerns related to reddening,         number of metal lines in the blue portion
tances will probably be obtained by          from high resolution spectra. In this           of the spectra (the stars at the turn-off of
comparing internal proper motions            case, temperatures may be derived e.g.          metal-poor Globular Clusters have
measured by HST with extensive radial        from the strength of the Balmer lines           spectra with very few measurable
velocity measurements obtained with          (good temperature indicators for stars          lines). Third, the location of Paranal
the stellar multi-object spectrograph GI-    warmer than about 5000 K), and metal            gives access to the closest Globular
RAFFE fed by FLAMES at KUEYEN
(VLT Unit Telescope 2). In the mean-
time, the best known method is the so-
called Main Sequence Fitting. In this
method, local subdwarfs whose paral-
laxes have been accurately measured
by the ESA HIPPARCOS astrometric
satellite are used as standard candles.
Assuming that these stars are identical
to main sequence stars in Globular
Clusters, distances may be derived by
the difference in the apparent magni-
tude. Since the luminosity of main se-
quence stars depends on temperature
and metallicity, we need to know these
quantities for both field and cluster
stars. Note that these quantities must
be derived differentially: what is impor-
tant is that temperature and metallicities
for field and cluster stars are on the
same scale; absolute values have a
much smaller impact. Up to now, all
data about cluster abundances were
based on giant stars; these values
might not be consistent with those de-
rived from dwarfs. Furthermore, temper-
atures are derived from colours; such a
derivation is sensitive to the value
adopted for interstellar reddening, but it
is not demonstrated whether the red-
dening scale used for Globular Clusters
is the same as for local subdwarfs, be-
cause the local subdwarfs lie within the
dust absorbing layer, while Globular         Figure 3: Observed colours of the Main Sequence at Mv = 6, as derived from local subdwarfs
Clusters are much farther. This leads to     with accurate parallaxes from HIPPARCOS and metal abundances [M/H] determined in our
about 6% uncertainty in the adopted dis-     programme. Filled symbols are stars actually used in the distance derivations; open symbols
tances. While this may appear as a           are control stars. The upper panel shows the run with metallicity for the Johnson B-V colour;
small value, it translates into uncertain-   the bottom panel is for the Strömgren b-y colour. Superimposed are the predictions by mod-
ties of almost 2 Gyr in the ages.            els by Straniero et al.


32
                                                                                            Figure 4: Fit of the Main Sequences of the
                                                                                            program Globular Clusters NGC 6397, NGC
                                                                                            6752 and 47 Tucanae, with local subdwarfs.
                                                                                            Left panels are for Johnson B-V colours;
                                                                                            right panels are for Strömgren b-y colours



                                                                                            band Johnson B-V and the intermediate
                                                                                            band Strömgren b-y colours. The
                                                                                            agreement between observations and
                                                                                            theoretical predictions is excellent, with
                                                                                            only a small offset for B-V. Note howev-
                                                                                            er that these relations are only used to
                                                                                            correct colours, i.e. differentially, so that
                                                                                            this small offset has no impact in our
                                                                                            analysis.
                                                                                               Figure 4 shows the fits we obtained
                                                                                            for the three clusters, in both the
                                                                                            Johnson (V, B-V) and Strömgren (V, b-
                                                                                            y) colour-magnitude diagrams. There
                                                                                            are small differences in the results ob-
                                                                                            tained with different colours that can be
                                                                                            attributed to small errors in the colour
                                                                                            transformations from observed to stan-
                                                                                            dard sequences in the used photome-
                                                                                            try. However, the agreement is on the
                                                                                            whole very good: distances estimated
                                                                                            with this procedure have errors as small
                                                                                            as 3.5%, and they are the best esti-
                                                                                            mates currently available for these
                                                                                            three clusters.

Clusters that are all located in the          error stems from uncertainties in the flat    Globular Cluster Absolute Ages
Southern hemisphere.                          fielding procedure, so that the error is      and their impact
   We addressed this issue in an ESO          fairly independent of the actual S/N of
Large Programme. UVES high resolu-            the spectra. However, averaging results          The ages of the three Globular
tion spectra were obtained for about          from all stars, we were able to constrain     Clusters that can be obtained from the
15–20 stars in each of the Globular           the temperatures for the stars in a clus-     luminosity of the turn-off point using
Clusters NGC6397, NGC6752 and 47              ter to within 30 K. This in turn translates   these distances are 13.8 ± 1.1 Gyr for
Tucanae. These three Globular Clus-           into unprecedented accuracies of about        NGC6397, 13.7 ±1.1 Gyr for NGC 6752,
ters were selected for observations be-       0.005 mag in the estimates of the inter-      and 11.2 ±1.1 Gyr for 47 Tuc. This last
cause they are the closest to the Sun,        stellar reddening E(B-V), and of about        cluster turns out to be about 2.5 Gyr
except M4, which however has a vari-          0.04 dex in the metal abundance [Fe/H].       younger than the other two, in excellent
able foreground reddening, making it          Furthermore, we derive the abundances         agreement with the age difference ob-
less suitable for precise dating. These       of important elements like O, Mg, Si,         tained by Rosenberg et al. (1999) using
three clusters cover a wide range in          Ca, and Ti, so that appropriate values of     relative dating methods.
metal abundance, from very metal-poor         the overall metal abundance could be             Leaving aside 47 Tucanae, the age of
([Fe/H]~ –2.0: NGC6397) to rather met-        obtained for each star.                       the two other clusters (that are coeval to
al-rich ([Fe/H]~ –0.7: 47 Tucanae).              Once reddening and metal abun-             the oldest Globular Clusters, accor-
NGC 6397 and NGC6752 belong to the            dances for both field stars and Globular      ding to Rosenberg et al. 1999) is
group of old clusters, while 47 Tucanae       Clusters were derived, distances could        13.7 ± 0.8 ± 0.6 Gyr, where the first er-
is likely slightly younger (Rosenberg et      be obtained by fitting the main se-           ror bar accounts for internal errors, and
al. 1999). In each of these clusters, we      quence of the Globular Clusters to the        the second one for systematics, includ-
selected for observations two groups of       location occupied by the field subd-          ing uncertainties in the stellar models.
stars, one near the turn-off, and the sec-    warfs. Only unevolved stars (that is          This estimate for the age of Globular
ond one at the base of the subgiant           stars with an absolute magnitude              Clusters coincides with the age of the
branch (see Figure 2). This choice al-        MV > 5.5) were considered, in order to        Universe determined by the WMAP
lowed us to make further tests on the         avoid possible concerns due to differ-        group for a standard ΛCDM model
program stars, described in the next          ences between the ages of field and           (Spergel et al. 2003). This indicates
Sections. In order to ensure that the         cluster stars. However, before this fitting   that, in the framework of a standard
analysis of the stars in these clusters is    is done, the temperature (colours) of the     ΛCDM model, the Galactic Globular
strictly identical to that of field subd-     field stars should be corrected to take       Clusters began to form very early, with-
warfs, we also acquired spectra of            into account the difference in metallicity    in 1.4 Gyr from the Big Bang.
about thirty such stars, selected to have     between the field and the Globular            Alternatively, this age estimate, com-
good Hipparcos parallaxes.                    Cluster stars. This was done using the-       bined with the estimate of the Hubble
   The analysis of the spectra of all these   oretical relations by Straniero et al.        constant given by the HST Key
stars was done using the same proce-          (1997): in Figure 3 we compare the pre-       Program (Freedman et al. 2001) and
dures: effective temperatures were de-        diction for the colour of the main se-        the WMAP experiment (Spergel et al.
rived from the wings of Hα, using the         quence at MV = 6 obtained with these          2003) can be used to constrain the val-
same precepts for both field and cluster      models with the observed colours of the       ue of the matter density ΩM in a flat
stars. From these analyses, we derived        field subdwarfs used in the distance          Universe Ωtot = ΩM + ΩΛ =1, as deter-
effective temperatures with errors of         derivations. We considered two inde-          mined by the spectrum of perturbations
about 150 K for each star. Most of this       pendent colours for each star: the broad      of the microwave background (Spergel

                                                                                                                                     33
et al. 2003). This estimate is independ-
ent from results provided by type Ia SNe                                                        Figure 5: Allowed values of ΩM as a
and clusters of galaxies. The results of                                                        function of H0 derived using our
this exercise are shown in Figure 5: ΩM                                                         estimate for the age of the oldest
is constrained to be ΩM < 0.57 (and ΩΛ                                                          Globular Clusters (13.7 ± 1.4 billion
> 0.43) at the 95% level of confidence.                                                         years), for a flat Universe (Ωtot = 1)
This confirms the need for some form of
dark energy (ΩΛ ≠ 0) providing the ob-
served acceleration in the expansion of
the Universe.
   Our distance estimates can also be
used to derive the luminosity of the hor-
izontal branch (a benchmark for dis-
tance scales, as well as for theoretical
models). When coupled with estimates
of the apparent magnitudes of RR Lyrae
stars in the LMC (e.g. using the deriva-
tion of Clementini et al. 2003 based on
photometric data acquired with the
Danish 1.5 m telescope and metallici-
ties derived from FORS spectra), they
can be used to derive the distance to         giants of NGC6397 (a metal poor clus-         mediate steps the participation of
the closest satellite to our Galaxy, the      ter with [Fe/H] = –2.0) may be used to        Carbon, Nitrogen, and Oxygen atoms.
first step in the extragalactic distance      test the effects of sedimentation. We         When the temperature is low (a few mil-
scale. The value we obtain is 50 ± 4          found that there is no appreciable dif-       lion degrees), as in the central regions
Kpc, the same value adopted in the            ference between the abundances of Fe          of main sequence stars like the Sun,
HST Key Project to derive the Hubble          and several other elements (Gratton et        only part of this cycle is active, due to
constant.                                     al. 2001). This severely constrains the       the large Coulomb barrier of Oxygen
                                              impact of diffusion. The most reason-         nuclei: practically, only Carbon and
No evidence for element                       able explanation for the lack of evi-         Nitrogen nuclei participate, and most of
sedimentation in Globular                     dence of sedimentation in stars of            the original Carbon is transformed into
Cluster stars                                 NGC6397 is that there is a region at the      Nitrogen because Nitrogen has a much
                                              base of the outer convective envelope         smaller cross section for proton capture
   The most important theoretical uncer-      mixed up by turbulence that cancels the       and then tends to accumulate. Howe-
tainty in the evolution of solar type stars   effects of sedimentation. Richard et al.      ver, at the higher temperatures of a few
concerns the impact of element sedi-          (2002) showed that such a mixing ef-          tens of millions of degrees K that may be
mentation due to microscopic diffusion.       fectively reduces the impact of micro-        reached in the H-shell burning of Red
Microscopic diffusion is a basic physical     scopic diffusion on both the ages of          Giants, Oxygen nuclei also participate in
mechanism; it needs to be included in         Globular Clusters and on the depletion        the cycle, and they are effectively trans-
the solar models in order to predict cor-     of the primordial Lithium abundances.         formed into Nitrogen nuclei too, because
rectly the very accurate and detailed run     This makes both ages and the interpre-        the cross section for proton capture is
of the sound velocity within the interior     tation of the Lithium abundances much         much larger than that for proton capture
of the Sun provided by helioseismology.       sounder.                                      on Nitrogen. Hence, material coming
Microscopic diffusion is a slow process                                                     from this region is depleted in Oxygen.
and its effects may take billion of years     A second generation of stars in               However, at the same temperature, pro-
to show up. Element sedimentation             Globular Clusters?                            ton capture on Neon nuclei effectively
causes two important effects: first,                                                        produces Sodium; hence this material
Globular Cluster ages computed from              Precise dating is not the only reason      will be rich in Sodium.
models that include the effect of micro-      why Globular Clusters are interesting.           It is not easy to bring material
scopic diffusion are about 1 billion years    They are also very dense stellar envi-        processed through the complete CNO
smaller than those obtained neglecting        ronments and this may cause system-           cycle to the surface of small mass red
this effect. Second, the abundances of        atic differences with respect to stars in     giants like those in Globular Clusters.
heavy elements for metal-poor stars           the general (low density) field. A very in-   The structure of the star in fact prevents
near the turn-off should be quite differ-     triguing difference concerns the anticor-     such a phenomenon, unless some deep
ent from those obtained for stars at the      relation between abundances of ele-           mixing not predicted by standard mod-
base of the subgiant branch, where the        ments like O and Na that the Lick-Texas       els (i.e. normal non rotating stars) oc-
inward deep penetration of the outer          group (Kraft, Sneden and co-workers:          curs. The reason is the large jump in en-
convective envelope should have can-          see Kraft 1994) found among the stars         tropy due to the variation of the molec-
celled the sedimentation effects due to       they observed in Globular Clusters            ular weight left over in the star by the
microscopic diffusion. This may have          (close to the tip of the red giant branch).   maximum extension of the central con-
important consequences, e.g. on the in-       Figure 6 illustrates this anticorrelation:    vective region when the stars left the
terpretation of the observed abun-            within Globular Clusters, stars that are      main sequence. Only when this molec-
dances of Lithium (see below). Detailed       rich in Oxygen are poor in Sodium, and        ular weight barrier is cancelled by the
predictions that takes into account par-      vice versa. Such an anticorrelation is        outward shift of the H-burning shell of
tial ionisation and the effects of radia-     not present among stars in the general        the star evolving along the red giant
tion pressure have been presented by          field and thus seems a peculiarity of         branch is deep mixing allowed. This re-
Richard et al. (2002): these authors          Globular Clusters (Gratton et al. 2000).      sult is fully confirmed by observations of
found that Fe is expected to be over-            The Oxygen-Sodium anticorrelation          the field stars (see Figure 7). Why then
abundant (and Li underabundant) by            is a sign of the presence of material         do stars in Globular Clusters behave
quite a large factor in turn-off stars with   processed throughout the complete             differently?
an initial value of [Fe/H]=–2 and an age      CNO cycle. In fact, at high tempera-             The critical observation is that of
of 12–14 Gyr.                                 tures, Hydrogen is burnt into Helium          dwarfs in Globular Clusters. In fact, the
   Our observations of turn-off and sub-      through a chain that includes as inter-       central temperature of these stars is still

34
Figure 6: Run of                                                                               is observed, that is in much smaller un-
the ratio between                                                                              evolved stars. This requires a transport
the abundances of                                                                              mechanism: the most likely is that the
Na and Fe, against                                                                             O-poor, Na-rich stars belong to a sec-
the ratio between                                                                              ond generation, born from the ejecta of
the abundances of                                                                              these massive AGB stars. These stars
O and Fe, for stars                                                                            should be a bit younger than the others:
in the Globular                                                                                however, the age difference that corre-
Cluster M13 (lower                                                                             sponds to the lifetime of 4–5 solar
panel), and in the                                                                             masses stars is tiny (only 100 or 200
field (upper panel).                                                                           million years), compared with the age of
Note that an                                                                                   the clusters (about 13 billion years).
extended O-Na an-                                                                              Such a small age difference would go
ticorrelation is                                                                               undetected as far as the magnitude and
present only                                                                                   colour of the turn-off in the colour-mag-
among Globular                                                                                 nitude diagram are concerned.
Cluster stars (from                                                                               This fascinating scenario for the evo-
Gratton et al.                                                                                 lution of clusters may help to under-
2000).                                                                                         stand one of the mysteries of Globular
                                                                                               Clusters, the so-called second parame-
                                                                                               ter. This concerns the horizontal branch
                                                                                               of Globular Clusters, the phase where
                                                                                               Globular Cluster stars burn helium at
                                                                                               their centres. Theory predicts that the
                                                                                               colour of stars along the horizontal
                                                                                               branch should be essentially deter-
                                                                                               mined by their metal content. In the six-
too low for complete CNO burning. If               base of the outer convective are            ties, Sandage, van den Bergh and oth-
then the O-Na anticorrelation is ob-               brought to the surface, and then lost at    ers noticed that there are pairs of
served also in these stars, the deep               low velocity by the slow wind blowing       Globular Clusters with apparently the
mixing hypothesis is untenable. We per-            from these stars. The escape velocity       same metal content, but very different
formed this test using the turn-off stars          from Globular Clusters is typically a few   colours of stars on the horizontal
we observed in NGC6752, a cluster that             tens of km/s, so that this material may     branch: the most famous pair includes
shows a clear O-Na anticorrelation                 be retained by these massive, concen-       M3 and M13. This anomaly indicates
among its giants. We found (see Figure             trated objects, explaining the difference   that there is a second parameter (other
8) that the O-Na anticorrelation is pres-          between cluster and field stars. Detailed   than metallicity) that determines the
ent also among dwarf stars, where it is            computations show that massive metal-       colour of the horizontal branch. This
actually very similar to what is observed          poor AGB stars may do the job. In some      mystery has gone unsolved for over 35
in giants (Gratton et al. 2001). It is then        way, this material should arrive where it   years. The differences in colours are
clear that the O-Na anticorrelation is not
due to deep mixing.
   What is then the source of the CNO
processed material we see in a large
fraction of the Globular Cluster stars?
The most probable sources are now ex-
tinct massive AGB stars (stars with
masses of 4–5 solar masses), where
large amounts of material processed
through the complete CNO cycle at the

Figure 7: Overabundances of various ele-
ments with respect to Fe vs. stellar luminos-
ity in field metal-poor stars. Stars evolve in-
creasing their luminosity, that is, from left to
right in these diagrams. The elements
shown are Li, C, N, O, and Na, as well as the
12
   C/ 13C isotopic ratios. Two mixing episodes
occur in these stars: 1) the first dredge-up
at the base of the giant branch is due to the
inward expansion of the outer convective
envelope, in zone where incomplete CN H-
burning has occurred during the main se-
quence. It only causes variations in the
abundances of C and N (and their isotopes),
and a decrease in the Li abundance. 2) A
second episode occurs later, when the H-
shell burning reaches the point of maximum
penetration of the convective envelope
(RGB bump); again, it only changes the
abundances of C, N, and Li. Surface Na and
O abundances are not modified during the
evolution of small mass stars (from Gratton
et al. 2000).

                                                                                                                                     35
Figure 8: Plots of spectral regions including Na lines (panel a) and O lines (panel b) in dwarfs of the Globular Clusters NGC6752. The stars
have virtually identical temperatures and chemical composition: the only difference is in the abundances of CNO elements and Na. Note that
the strengths of the Na and O lines are anticorrelated each other: this trend is similar to that found in giants. Since the temperatures at the
centres of these stars are not large enough for complete CNO cycle, the Na-rich, O-poor stars must contain material processed elsewhere
(from Gratton et al. 2001).

essentially due to differences in masses        utes, the Universe was hot and dense             stars even in nearby Globular Clusters.
of the stars on the horizontal branch:          enough to undergo nuclear reactions              Our analysis of the Li abundance in the
however, the reason for these different         that formed 2H, 3He, 4He and 7Li.                TO stars of NGC 6397 showed that
masses is not clear. In some cases, a           Production of heavier nuclei was not             they share the same Li abundance
difference in age may be the explana-           possible because of the rapid cooling of         (within errors), and there is very little
tion. However, it has been shown by             the Universe. According to Standard Big          room for dispersion above the observa-
several authors that M3 and M13, for            Bang Nucleosynthesis (SBBN), in the              tional errors. Out of the 15 TO stars so
examples, have the same age.                    presence of three massless neutrinos,            far observed in this cluster none has
   A second generation born from the            the primordial abundance of these light          been found to be strongly Li depleted.
material expelled from massive AGB              nuclei depends only on the baryon to             This result therefore supports the pri-
stars might explain the anomalous blue          photon ratio in the Universe, i.e. on the        mordial nature of the Li observed in
horizontal branch of clusters like M13,         number of baryons, since the number of           these stars. From this value we deter-
that has indeed a large population of O-        photons is known from the temperature            mined a value of the baryonic density
poor, Na-rich stars. In fact this second        of the cosmic microwave background               that is consistent at 1.3 σ with the value
generation of stars should also be en-          (CMB). Therefore a determination of the          determined from the WMAP experi-
riched in Helium, produced by the H-            primordial abundance of the light nuclei         ment.
burning. Stars richer in Helium evolve          allows us, in principle, to determine Ωb.
faster than normal stars: stars currently       Spite & Spite (1982) found that the              References
on the red giant branch would then be           warm metal-poor halo dwarf stars show
less massive, by a few hundredths of a          the same lithium abundance independ-             Bonifacio P. et al. 2002, A&A, 390, 91
                                                                                                 Clementini, G., Gratton, R.G., Bragaglia, A.,
solar mass. Not a large amount, but well        ent of temperature or metallicity, the              Carretta, E., Di Fabrizio, L., & Maio, M.
enough to justify a very different colour       most straightforward explanation being              2003, AJ, 125, 1309
when these stars are on the horizontal          that the lithium observed in these stars         Freedman, W.L. et al. 2001, ApJ, 553, 47
branch. Note however that M13 has vir-          is the primordial lithium. This view may         Gratton, R.G., Carretta, E., Matteucci, F. &
tually no star on the red side of the hor-      be challenged since the Li abundance                Sneden, C. 1996, in Formation of the
izontal branch, so that this effect alone       in these stars might have been de-                  Galactic Halo… Inside and Out, H.
cannot solve the second parameter               creased by various stellar phenomena                Morrison & A. Sarajedini eds., ASP Conf
problem.                                        (stellar winds, convective and/or rota-             Ser. 92, 307
   Of course many more observations             tional mixing, diffusion, destruction in         Gratton, R.G., Sneden, C., Carretta, E., &
                                                                                                    Bragaglia, A. 2000 A&A, 354, 169
are required to confirm this scenario.          deep layers) and possibly increased by           Gratton, R.G. et al. 2001, A&A, 369, 87
FLAMES, using both UVES and GI-                 production through cosmic rays.                  Kraft, R.P. 1994, PASP, 106, 553
RAFFE spectrographs, is particularly            Theories that predict Li depletion in            Perlmutter et al. 1999, ApJ, 517, 565
well suited for such observations. ESO          metal poor stars imply the existence of          Richard, O., Michaud, G., Richer, J.,
telescopes will likely play a basic role in     a dispersion in Li abundances and the               Turcotte, S., Turck-Chieze, S., &
future observations of Globular                 existence of a small number of highly               VandenBerg, D.A. 2002, ApJ, 568, 979
Clusters.                                       depleted stars, as observed among                Rosati, P., Borgani, S., & Norman, C. 2002,
                                                halo field stars. In this respect a                 ARA&A, 40, 539
                                                                                                 Rosenberg, A., Saviane, I., Piotto, G., &
Globular Clusters and Ωb                        Globular Cluster is an ideal testing
                                                                                                    Aparicio, A. 1999, AJ, 118, 2306
                                                ground for such theories, since it al-           Spergel, D.N. et al. 2003, submitted to ApJ
  Besides ΩM, Globular Clusters may             lows us to observe a population of the              (astro-ph/030229)
be useful to determine the value of the         same age and metallicity. However, the           Spite M. & Spite F., 1982 Nature, 297, 483
baryonic component of the density of            full power of the VLT is required to ob-         Straniero, O., Chieffi, A., & Limongi, M. 1997,
the Universe, Ωb. In its first three min-       tain high quality spectra of the faint TO           ApJ, 490, 425



36
Intracluster Planetary Nebulae in the Virgo
Cluster: Tracers of Diffuse Light
M. ARNABOLDI1,2, O. GERHARD 3, K.C. FREEMAN 4
1
 I. N. A. F., Osservatorio Astronomico di Torino, Turin, Italy; 2I. N. A. F., Osservatorio Astronomico di Capodimonte,
Naples, Italy; 3Astronomisches Institut, Universitat Basel, Binningen, Switzerland; 4RSAA, Mt Stromlo
Observatory, ACT, Australia

Discovery of diffuse light
in clusters

    Stars are usually observed to form in
galaxies (discs, dwarfs and starbursts).
In nearby galaxy clusters, however, a
diffuse intracluster stellar component
has been detected from deep imaging
and observations of individual intraclus-
ter stars.
    Intracluster light (ICL) is potentially of   Figure 1: The emis-
great interest for studies of galaxy and         sion spectrum of the
galaxy cluster evolution. The dynamical          compact Virgo clus-
evolution of cluster galaxies involves           ter HII region
complex and imperfectly understood               obtained with UT4
processes such as galactic encounters,           and FORS2.
tidal stripping and cluster accretion.
Various studies have suggested that
between 10% and 50% of a cluster’s to-           cluster collapse, or are they removed         tal IC light. Also, through the [OIII]
tal luminosity may be contained in the           gradually over time via “galaxy harass-       λ5007 Å planetary nebulae luminosity
ICL, with a strong dependence on the             ment”? Do all of these stars have parent      function (PNLF), PNe are good distance
dynamical state of the cluster. The prop-        galaxies or do they form in situ? The re-     indicators, and the observed shape of
erties of the ICL may also be sensitive          cent discovery of an isolated compact         the PNLF provides information on the
to the distribution of dark matter (DM) in       HII region in the Virgo cluster (Gerhard      line of sight distribution of the IC
cluster galaxies, as simulations have            et al. 2002) has shown that some star-        starlight.
shown that the structure of DM halos in          formation activity can indeed take place         IC PNe are useful tracers to study the
galaxies plays a central role in the for-        in the outskirts of galaxy halos if not al-   spatial distribution, kinematics, and
mation and evolution of tidal debris.            ready in Virgo IC space. The spectrum         metallicity of the diffuse stellar popula-
    Recently progress has been made in           of this isolated compact HII region is        tion in nearby clusters. Different cluster
the study of intracluster star light on          shown in Figure 1. This HII region is         formation mechanisms predict different
several fronts. Individual intracluster          powered by a small star cluster of ~ 400      spatial distributions and velocity distri-
stars, including planetary nebulae de-           M , involving only 1 or 2 O stars, with       butions for the IC stars. If most of the IC
tected from the ground and red giants            an estimated metallicity of Z = 0.4. The      light originates in the initial cluster col-
detected using HST, have been discov-            age of this HII region is ~ 3 Myr and it      lapse, its distribution and kinematics
ered in the Virgo cluster. These intra-          will probably dissolve by internal            should follow closely that of galaxies in
cluster (IC) stars give the promise of           processes in a few 108 yr: its stars and      the cluster. On the other hand, if the IC
studying in detail the kinematics, metal-        metals will then be added to the diffuse      light builds slowly with time because of
licity and age of the intracluster stellar       stellar population nearby. The location       galaxy harassment and tidal stirring,
population in nearby galaxy clusters,            of this object in the Virgo field is shown    then a fraction of IC light may still be lo-
and thereby learning about the origin of         in the ESO press release 02/03.               cated in long streams, and dynamically
this diffuse stellar component and the                                                         unmixed structures should be easily vis-
details of the cluster origin.                   Intracluster Planetary Nebulae                ible in phase space.
                                                 as tracers of cluster evolution
Direct observations of stars in                                                                Narrow-band wide-field surveys
Virgo field                                         Intracluster planetary nebulae (IC            We have embarked on a narrow-
    Ferguson, Tanvir & von Hippel (1998)         PNe) have several unique features that        band [OIII] imaging survey in the Virgo
first looked for individual RGB stars in         make them ideal for probing intracluster      cluster (Figure 2), with the aim of deter-
intracluster space. Using a HST deep             starlight. The diffuse envelope of a PN       mining the radial density profile of the
F814W (I-band) image of a “blank” field          re-emits 15% of the UV light of the cen-      diffuse light, and gaining information on
located 45’ east of the central Virgo            tral star in one bright optical emission      the velocity distribution via subsequent
Cluster galaxy M87, they were able to            line, the green [OIII] λ5007 Å line. PNe      spectroscopic observations of the ob-
detect an excess of point sources rela-          can therefore readily be detected in ex-      tained samples. Given the use of the
tive to the HDF-north caused by the              ternal galaxies out to distances of 25        PNLF as distance indicators, we also
presence of IC red giants. Follow-up             Mpc and their velocities can be deter-        obtain valuable information on the 3D
studies on a different IC field 41n north-       mined from moderate resolution                shape of the Virgo cluster from these IC
west of M87 confirmed an excess of ob-           (λ/∆λ~5000) spectra: this enables kine-       PN samples (see also Feldmeier et al.
jects (with respect to background HDF-           matical studies of the IC stellar popula-     1998).
N and HDF-S fields) with I ≥ 27.                 tion.                                            Wide-field mosaic cameras, such as
    Are these stars tidally stripped from           PNe trace stellar luminosity and           the WFI on the ESO MPI 2.2 m tele-
galaxies during the early phases of              therefore provide an estimate of the to-      scope and the Suprime Cam on the


                                                                                                                                       37
Figure 2: Our surveyed                                                                      the Tully-Fisher relation.
fields in the Virgo cluster.                                                                   What is the fraction of Ly-α emitters
The two upper fields were                                                                   in the first magnitude of the LF for the
obtained at the ESO MPI                                                                     Virgo IC PNe samples ? When we com-
2.2m telescope, and the                                                                     pute the fraction of Ly-α emitters which
lower-right field with the                                                                  can contaminate the ICPN candidate
Suprime Cam at the 8.2                                                                      sample selected as outlined in section
m Subaru telescope. The                                                                     2.1, it amounts to about 15% of the ob-
lower-left field is from                                                                    served sample. This estimate is sup-
Feldmeier et al. (1998)                                                                     ported by the empty field survey of
and was used to test the                                                                    Castro-Rodriguez et al. (2003).
selection criteria on the
spectroscopically                                                                           Properties of the diffuse light
confirmed IC PNe in                                                                         in Virgo cluster
Arnaboldi et al. (2002).
Several more fields need                                                                        A primary goal is to estimate the frac-
to be surveyed to deter-                                                                    tion of light from intracluster stars in the
mine the large scale sur-                                                                   surveyed region of the Virgo cluster. In
face density distribution                                                                   our 0.25 deg2 field at a distance of 1°
of the ICL in the Virgo                                                                     from the cluster centre, the IC PNe
cluster.                                                                                    sample indicates a total associated lu-
                                                                                            minosity of 5.8–7.5 ×109 LB, , which
Subaru 8.2 m, allow us to identify the IC   the first time at the VLT-UT4 with              corresponds to a surface luminosity of
PNe associated with the extended ICL        FORS2 by Arnaboldi et al. (2003). We            0.33–0.57 LB, /pc2 or a surface bright-
(Arnaboldi et al. 2002, 2003; Okamura       conclude that the existence of IC PNe in        ness of µB,* = 28–27.7 mag/arcsec2. As
et al. 2002). These surveys require the     the Virgo cluster is now beyond doubt.          discussed by Arnaboldi et al. (2002),
use of data reduction techniques suited        Why then did the spectroscopic study         over the range of radii probed by the
for mosaic images, and also the devel-      by Kudritzki et al. (2000) find only back-      survey fields, the luminosity surface
opment and refining of selection criteria   ground galaxies? The answer lies in ex-         density of galaxies in Virgo decreases
based on colour-magnitude diagrams          amination of the luminosity function (LF)       by a factor of ~3, while that for the IC
(CMD) produced with SExtractor.             of their objects. The LF of the candi-          PNe is nearly constant. Therefore, from
   Through this work, the on-band/off-      dates studied by Kudritzki et al. (2000)        the data available so far, the IC PNe in
band [OIII] imaging technique which         follows closely the LF of field Ly-α emit-      Virgo are not centrally concentrated;
has been used for PNe identification in     ters at z = 3.1; see Figure 4.                  however we need to investigate fields at
Virgo and Fornax ellipticals has led to        We can compare the LF for the Ly-α           larger radii to constrain the total amount
the following selection criteria for the    emitters with the LF for the 16 spectro-        of IC light.
most reliable detection of IC PNe candi-    scopically confirmed IC PNe of the                  One needs to compare the luminosi-
dates:                                      Feldmeier et al. (1998) sample. These           ty derived for the diffuse population with
   1. the source should be unresolved;      confirmed IC PNe are mostly brighter            the luminous contribution from Virgo
   2. the source should have an emis-       than the brightest of the Ly-α emitters         galaxies. If IC PNe are produced by
sion line equivalent width (EW) larger      shown in Figure 4. The brightest of the         phenomena acting locally, as the struc-
than 100 Å. This is evaluated by meas-      emission line candidates studied by             ture in the IC PNe distribution shown in
uring the ([OIII] - V) colour between a     Kudritzki et al. (2000) is 0.5 mag fainter      Okamura et al. (2002) seems to sup-
detected object in the on-band [OIII] im-   than the bright cut-off in the PNLF for         port, then the fraction of diffuse light
age and the signal in the corresponding     M87, and 0.8 mag fainter than the bright        with respect to the computed light in
position in the off-band V image. The       cut-off for the spectroscopically con-          galaxies in the field is about 10%. On
EW criterion corresponds to a filter-de-    firmed IC PNe in the Virgo cluster. Most        the other hand, comparing the IC sur-
pendent colour excess relative to field     of the current IC PN candidates in Virgo        face brightness with the smoothed out
stars;                                      are within 1 mag of the bright cut-off in       surface brightness of galaxies from
   3. there should be no source detect-     the PNLF. This is the reason why                Bingelli et al. (1987) gives an upper lim-
ed in the V-band image at the position      Kudritzki et al. did not find IC PNe. Their     it of about 40%.
of the detected [OIII] source.              sample was dominated by the Ly-α                    Is the diffuse light in the Virgo cluster
   The requirement on EW greatly re-        emitters which are
duces the contamination from [OII] star-    more abundant at
burst emitters at z ~ 0.35. The colour      fainter      magni-
selection must take into account the        tudes. (See also
photometric errors in the final on-image,   Arnaboldi et al.
via simulation of unresolved sources.       2002).
                                               The bright cut-
Spectroscopic confirmation                  off of the LF for the
and first results                           Virgo IC PNe is
                                            about 0.3 mag
   The spectroscopic observations of        brighter than for
the Feldmeier et al. (1998) Virgo IC PNe    the PNe in individ-
sample, carried out by our group using      ual Virgo galaxies.
2dF and the AAT, showed that most of        This is believed to
the emission line sources in this sample    be due to the elon-
are indeed IC PNe, because the com-         gated structure of
bined spectrum of all the “sharp line”      the Virgo cluster,
emitters clearly showed the [OIII]          as        previously
4959/5007 Å doublet. In 2002, a high        found for the distri- Figure 3: Spectrum of the confirmed intracluster PN in the Virgo clus-
S/N spectrum for a single IC PN in the      bution of Virgo spi- ter. The [OIII] doublet and the Hα emission are visible in this high S/N
Virgo cluster (Figure 3) was obtained for   ral galaxies using spectrum from UT4 and FORS2.

38
Figure 4: The solid line                                                                         ity distribution of ICPN candidates in
shows the expected LF of                                                                         Virgo. The VLT instruments, FLAMES
the field Ly-α population at                                                                     and VIMOS, will be most important in
redshift z = 3.1 for objects                                                                     giving us the radial velocity distribution
with V < 24.73. The faint                                                                        of the stars in the diffuse component,
dotted line shows the ex-                                                                        identifying individual streams, and pro-
pected Ly-α LF without                                                                           viding us with samples of the phase
any magnitude constraints                                                                        space for the diffuse component at dif-
in the V band. Asterisks in-                                                                     ferent cluster radii. These observational
dicate the LF of                                                                                 results will be compared with N-body
spectroscopically                                                                                high resolution cosmological simula-
confirmed Ly-a emitters                                                                          tions and in this way we should be able
from Kudritzki et al.                                                                            to determine how old dynamically the
(2000). Filled dots and dia-                                                                     diffuse light is.
monds show the LF of Ly-
α emitters in two other                                                                          Acknowledgements
blank-field surveys. These
are all consistent; from Castro-Rodriguez et al. (2003).                                            The authors wish to thank ESO for
                                                                                                 the support of this project and the ob-
                                                                                                 serving time allocated both at La Silla
distributed uniformly? Recent discover-             cluster stellar light is mostly dynamical-   and Paranal telescopes. We are grate-
ies of low surface brightness arcs in oth-          ly unmixed and clustered in structures       ful to the ESO 2.2 m telescope team for
er nearby clusters, significant field-to-           on scales of about 50 kpc at a radius of     their help and support during observa-
field variations in the number density of           400–500 kpc from the cluster centre.         tions, in particular E. Pompei and H.
Virgo IC PNe, and the remarkably inho-              The simulations predict the radial veloc-    Jones. M. A. and O. G. thank R. Scarpa
mogeneous distribution of IC PNe in the             ity distribution expected in spectroscop-    for efficient help at UT4. We would also
field surveyed by Okamura et al. (2002)             ic follow-up surveys. When we compare        like to thank all our collaborators. This
(see Figure 5) have demonstrated that               the spatial clustering in the simulation     work has been supported by the
intracluster stars are not distributed uni-         with the properties of the Virgo IC stel-    Schweizerischer Nationalfonds and by
formly.                                             lar population, we find a substantial        INAF.
   An emission line survey carried out              agreement.
on an empty field in the Leo group, us-                                                          References
ing the same selection criteria as adopt-           Conclusions
ed for the Virgo cluster survey, gives an                                                        Arnaboldi, M., et al. 2002, AJ, 123, 760
upper limit on the diffuse surface lumi-               The results obtained so far from IC       Arnaboldi, M., et al. 2003, AJ, 125, 514
nosity of 4.4 ×10–3 LB, /pc2, correspon-            PNe samples have shown that i) the           Bingelli, B., Tammann, G. A., Sandage, A.
ding to a surface brightness limit µB,* >           fraction of the diffuse light in the Virgo     1987, AJ, 94, 251
32.8 mag/arcsec2 (Castro-Rodriguez et               cluster amounts to 10%-40%; ii) the in-      Castro-Rodriguez, N. et al. 2003, A&A, in
al. 2003). This empty field survey, ob-             tracluster stars of Virgo are not central-     press (astro-ph/0304057)
served at the peak of the HI distribution           ly condensed and not uniformly distrib-      Ferguson, H., Tanvir, N., von Hippel, T. 1998,
in the Leo intragroup cloud, gives an up-           uted and iii) the front edge of the Virgo      Nature, 391, 461
                                                                                                 Feldmeier, J. J., Ciardullo, R., Jacoby, G. H.
per limit on the fraction of diffuse light in       cluster is about 20% closer to us than
                                                                                                   1998, ApJ, 503, 109
this intra group field of < 1.6%. The ev-           M87. A high-resolution collisionless N-      Gerhard, O. et al., 2002, ApJ, 580, L121
idence coming from the Leo group is                 body simulation of a Virgo-like cluster at   Kudritzki, R.-P., et al. 2000, ApJ, 536, 19
very interesting because it shows that              z = 0 predicts strong substructure in        Napolitano, N. R., et al. 2003, ApJ, in press
the fraction of diffuse light vs. light in in-      phase space, so our next goal will be to       (astro-ph/0305216)
dividual galaxies that we find in Virgo is          look for substructure in the radial veloc-   Okamura, S. et al. 2002, PASJ, 54, 883
related to the Virgo cluster and its evo-
lution. It does not appear to be a gener-
al physical property of the local uni-
verse.
   A high resolution simulation of a
Virgo-like cluster in a LCDM cosmology
was used to predict the velocity and the
clustering properties of the diffuse stel-
lar component in the intracluster region
at the present epoch (Napolitano et al.
2003). The simulated cluster builds up
hierarchically and tidal interactions be-
tween member galaxies and the cluster
potential produce a diffuse stellar com-
ponent free-flying in the intracluster
medium. We find that at z = 0 the intra-

Figure 5: Deep [OIII] image in the Virgo
central core region. The IC PN candidates
are marked by circles. Envelopes of bright
galaxies have been subtracted. The over-
density in the upper right quadrant of this
field is highly significant. The majority of can-
didates in this field seem to be related to the
M86-M84 region of the Virgo cluster, sup-
porting a local origin for the IC PNe.

                                                                                                                                           39
The Red-Sequence Cluster Survey
FELIPE BARRIENTOS1, MICHAEL GLADDERS2, HOWARD YEE 3, ERICA ELLINGSON4,
PATRICK HALL1,5, LEOPOLDO INFANTE1
1
 P.Universidad Católica de Chile; 2Observatories of the Carnegie Institution of Washington; 3University of Toronto;
4
 University of Colorado; 5Princeton University

   Galaxy clusters are the largest and           important new insights on hitherto poor-       shift, N(M,z), is strongly dependent on
most massive discrete structures in the          ly measured or unknown phenomena.              the cosmological parameters Ωm and
Universe. They represent the endpoint            Despite the large area of the survey (90       σ8. Ωm describes the matter density of
of gravity’s influence on the growth and         square degrees of sky - roughly 500            the Universe, and σ8 describes the am-
collapse of the Universe’s large scale           times the apparent area of the full            plitude of the early fluctuations in the
structure. Mass in the Universe, as              Moon) a very efficient observing strate-       Universe, which seed the growth of
traced by galaxies, is distributed in            gy allowed this unprecedented area to          structures on the physical scale of
sheets surrounding large, nearly empty           be covered in only 25 nights of observ-        galaxy clusters. In an expanding low-
spherical voids. At the intersection of          ing time. Two telescopes were used to          density universe (small Ωm), structures
these sheets, at places referred to as fil-      complete the project (the Canada-              like galaxy clusters must form relatively
aments, the density of the universe is           France-Hawaii 3.6 m telescope for the          early, when the universe was still com-
even larger. At the intersection of fila-        northern hemisphere, and the Cerro             pact and relatively dense. Only in this
ments, sitting much like spiders in a            Tololo Inter-American Observatory 4 m          setting does such a universe have suf-
3-D cosmic web, are galaxy clusters.             telescope for the southern hemisphere).        ficient mass density to cause large
Clusters are extremely dense, with cen-          The survey began in mid-1999, and ob-          structures to collapse under the influ-
tral densities ∼1000 times that of their         servations were finished by late 2001.         ence of gravity, and even then only if the
surroundings. As the Universe ages,              We are currently using the powerful            initial fluctuations which seed the
galaxy clusters are thought to become            ESO VLT telescopes for following up            growth of structure are relatively large
larger and larger, as mass drains along          some of the highest redshift clusters in       (high σ8). Conversely, in a universe with
the filaments into the central clusters.         the sample.                                    much greater mass content (large Ωm)
Galaxy clusters are extremely important                                                         structure continues to form as the uni-
laboratories for the study of a number of        The method                                     verse expands and ages, even when
questions in astronomy, and will be one                                                         the seed fluctuations are relatively mod-
of the most important targets for obser-            In conjunction with the extensive data      est (low σ8).
vations by both ground-based and                 from the RCS project, we have devised             We have known for a long time that
space observatories in the coming                a new algorithm for finding clusters in        the local universe contains many galaxy
years.                                           two-filter survey data. This algorithm ex-     clusters. These clusters could result
   The Red-Sequence Cluster Survey is            ploits the fact that all clusters so far ob-   from either a low matter density, large
an ambitious project designed to identi-         served have a central population of old        fluctuation cosmology, or a high matter
fy a large sample of galaxy clusters over        red galaxies. While the properties of the      density, small fluctuation cosmology.
a wide range of redshifts (distances).           overall cluster galaxy population do           However, as described above, the past
The resulting sample of galaxy clusters          evolve with redshift (i.e. the fraction of     history of this local cluster population is
will yield answers about the way in              blue or actively star-forming galaxies is      wildly different in these two cosmolo-
which structures formed and grew in the          generally higher at higher redshift), in all   gies, and so studies of clusters at great
Universe, and will facilitate a number of        well-formed significant clusters so far        distances (which, due to light travel-
other projects. The survey is the largest        observed there is a red population. In         time effects also corresponds to the dis-
area survey ever conducted on 4-m                essence, we define a cluster as an             tant past) offer a powerful constraint on
class telescopes, and as such will yield         overdensity in both position and colour.       cosmological models. The RCS seems
                                                 The distribution of galaxy clusters, even      to contain many high-redshift, massive
                                                 in systems with a large fraction of blue       clusters, and hence initial results
                                                 galaxies, represents a colour distribu-        strongly favour a low Ωm and high σ8
                                                 tion not generally found in the field (i.e.    universe. However, this conclusion de-
                                                 non-cluster) galaxy population. Addi-          pends critically on correct mass esti-
                                                 tionally, the filters used for the RCS sur-    mates for these systems, and our ongo-
                                                 vey provide a particularly deviant (and        ing spectroscopy with the VLT+FORS2,
                                                 hence readily identified) colour for clus-     for which the first data have just been
                                                 ters at modest to very high redshifts.         taken, represents a critical step in con-
                                                 Thus, simple colour cuts allow us to se-       firming this initial result. A summary of
                                                 lect 2-D groupings of red galaxies,            the first clusters with confirmed red-
                                                 which are very likely to be real 3-D clus-     shifts is shown in Figure 1.
                                                 ters of galaxies at high redshifts. We
                                                 have tested this method extensively us-        Cluster Galaxy Evolution
                                                 ing both real redshift survey data, and
                                                 using complex and thorough simula-                Clusters of galaxies also provide us
                                                 tions, and find that it works extremely        with natural laboratories to study galaxy
Figure 1: Spectroscopic confirmation of the      well (a detailed description of the            evolution, since we find a number of
first clusters found in the RCS. The meas-       method can be found in Gladders & Yee          galaxies in a relatively small region of
ured spectroscopic redshift for the clusters     2000).                                         the universe that can be traced to high
in this sample agrees very well with the esti-                                                  redshift, or equivalently to an epoch
mates obtained from the photometric data         Clusters and Cosmology                         when the universe was much younger.
alone. We are currently working with the VLT                                                       Our studies are focussed on measur-
and FORS2 to populate this diagram in the           The number density of galaxy clus-          ing properties such as the galaxy lumi-
region at z > 0.9.                               ters as a function of their mass and red-      nosity function (LF), blue fraction, and

40
                                                                                             symbols are the galaxies in the cluster
                                                                                             at z = 0.97 and the blue crosses are
                                                                                             their equivalent in local clusters of
                                                                                             galaxies. The red solid line and the bro-
                                                                                             ken blue line are the best fit for the
                                                                                             galaxies at z = 0.97 and for those in lo-
                                                                                             cal clusters, respectively, keeping the
                                                                                             same slope for both sets of galaxies.
                                                                                             The offset between the lines is approxi-
                                                                                             mately 1.2 magnitudes. This brightness
                                                                                             shift can be interpreted as the galaxies
                                                                                             at z = 0.97 following a similar size-mag-
                                                                                             nitude relation than those in local clus-
                                                                                             ters but being 1.2 magnitudes brighter
                                                                                             than their local counterparts. Much like
                                                                                             the colour evolution, this is consistent
                                                                                             with models of early formation of the
                                                                                             stellar population in these galaxies, with
                                                                                             subsequent fading and reddening as
                                                                                             they age.

                                                                                             Strong-Lensing Clusters

                                                                                                The large area and depth covered by
                                                                                             the RCS provides large samples of
                                                                                             galaxy clusters spanning a wide range
                                                                                             of properties. A particularly interesting
                                                                                             subsample is the strong-lensing clus-
                                                                                             ters, which due to gravitational effects
                                                                                             act as lenses magnifying and distorting
                                                                                             the images of distant objects back-
Figure 2: IJK colour composite image of the field centred on RCS0439.6-2905. North is up
                                                                                             ground to the cluster. We have so far
and East to the left. This image shows approximately the central 1.1 × 1.1 Mpc.
                                                                                             found 8 new strong lensing systems in
                                                                                             the RCS, some of them with the pres-
the CMR (colour-magnitude relation,            niques. The galaxies selected as ellipti-     ence of multiple giant arcs (Gladders et
i.e. red sequence), for clusters over a        cal or lenticular galaxies (E/S0s) on the     al. 2003). The incidence of such a large
range of richnesses and redshift (indi-        basis of their 2-D light profiles are         number of strong lensing clusters in the
vidually for rich clusters, in redshift bins   shown as red circles. Clearly these           surveyed area is discrepant with current
for poor clusters). These data will allow      galaxies define a tight colour sequence       theoretical predictions (standard expec-
investigations of the evolution of cluster     in this cluster. The red sequence as it       tations are 0-1 such clusters in a survey
galaxies, and will constrain their forma-      would appear at the distant redshift for      the size of the RCS).
tion time and process through a detailed       the E/S0 galaxies in the Coma cluster, a         The first studied RCS lensing cluster,
analysis of the evolution of the slope,        nearby cluster of galaxies and the            RCS0224.5-0002, is shown in Figure 5.
scatter and colour of the CMR. As the          canonical example of a rich cluster, is       Spectroscopy of this cluster was ac-
sample will be volume limited for rich         shown as the blue broken line. The            quired using the 8.2 m Kueyen
clusters over a large portion of the red-      galaxies in RCS0439.6-2905 appear in-         Telescope and FORS-2 in Director’s
shift range, we will be able to trace clus-    trinsically     slightly
ter galaxy evolution without strong se-        bluer than those in
lection biases.                                the Coma cluster,
                                               consistent with these
RCS0439.6-2905: A Cluster                      galaxies being like
Galaxy Evolution Case Study                    those seen in Coma,
                                               but at a much youn-
   As an example of such studies we            ger age.
present in Figure 2 an image of                   The excellent im-
RCS0439.6-2905, one of the most mas-           age quality of the
sive distant clusters found in the RCS.        VLT not only allowed
Recent spectroscopy confirms that              us to segregate the
RCS0439.6-2905 is at z = 0.97 making           E/S0 galaxies in this
it more distant than all but a handful of      cluster at z = 0.97 but
known galaxy clusters. The I, J and K-         also to determine the
band colour composite in Figure 2 (I-          size of the galaxies.
band taken at Magellan and J and K-            The size of the galax-
bands at the VLT) shows numerous               ies, accounting for
galaxies with similar colours that pre-        the seeing profile, is
sumably are cluster members.                   given by the effective Figure 3: IR colour-magnitude diagram in the field of RCS0439.6-
   Figure 3 shows the colour-magnitude         radius, the radius 2905. All the objects are included and shown as filled circles. The
relation for the galaxies in the field of      that encloses half of morphologically selected E/S0 galaxies are shown as open cir-
this cluster. The quality of the images        the light of the cles. These galaxies define a tight sequence, similar to that found
taken with the VLT was very good, with         galaxy, and is show in local clusters. The solid line shows the best fit to the sequence
a seeing of ∼ 0.4 arcsec, and this allows      in Figure 4 as a func- of E/S0 galaxies in the cluster. The broken line corresponds to the
us to perform a morphological study by         tion of their absolute colour-magnitude relation for the E/S0 galaxies in Coma cluster
applying galaxy image fitting tech-            magnitude. The red redshifted to z = 0.97.

                                                                                                                                     41
                                                                                                 Figure 4: Size-magnitude diagram for the
                                                                                                 E/S0 galaxies (filled circles) in the field of
                                                                                                 RCS0439.6-2905. The size has been ob-
                                                                                                 tained from the 2-D galaxy light profile fitting
                                                                                                 algorithm. For comparison the E/S0 galaxies
                                                                                                 in local clusters are show as crosses, in-
                                                                                                 cluding the best linear fit to these galaxies
                                                                                                 (broken line). The solid line corresponds to
                                                                                                 the fit for the galaxies in RCS0439.6-2905,
                                                                                                 constrained to have the same slope as that
                                                                                                 for the local E/S0 galaxies. There is an off-
                                                                                                 set for the fit at z = 0.97 from the local rela-
                                                                                                 tion that amounts to ∆MB(AB) = –1.20 ± 0.09.




Discretionary Time, soon after the clus-        Additional Projects: Clustering                     As is well known, the distribution of
ter was discovered. This initial spec-          and Evolution of Small Galaxy                    galaxies in the universe is believed to
troscopy demonstrated that the cluster          Groups                                           be different from the distribution of dark
was at z = 0.773, and showed that one                                                            matter; the distribution of galaxies is a
of the arcs (the arc labelled ’C’, visible        The wide area, depth and homo-                 biased tracer of the matter. To under-
in Figure 5) was extremely distant, at a        geneity of the RCS data allow us to pur-         stand the clustering pattern of galaxies
redshift of 4.8786 (Gladders et al.             sue other relevant problems in galaxy            through a good interpretation of obser-
2002). The FORS spectrum of this arc            evolution, such as the study of the for-         vational data and to compare them to
at Ly-α is shown in Figure 6, along with        mation and evolution of structure in the         current predictions of cosmological
the images of the arc in the R and I-           Universe, ranging from clusters,                 models, this bias has to be understood.
bands. The Ly-α emission (shown by              groups, pairs of galaxies to individual             In simulations, pairs, triples, small
both the spectrum and the R-band                galaxies.                                        groups, groups and clusters of galaxies
light), with an equivalent width of sever-
al hundred Angstroms, is spatially ex-
tended compared to the UV continuum
just to the red of Ly-α (shown by the I-
band light). At the time of discovery,
RCS0224.5-0002 was the most distant
cluster known with such spectacular
strong lensing, and the high redshift arc
was one of only two known giant arcs at
such great distances, the other being an
arc at z = 4.92 formed around the
z = 0.33 cluster CL 1358+62 (Franx et
al. 1997). Notably, the distant arc in
RCS0224.5-0002 appears rather differ-
ent in detail; it is spatially smooth with an
extended Ly-α halo surrounding a com-
pact star-forming core, and shows no
velocity structure, whereas the in CL
1358+62 is knotty in appearance and
shows velocity structure of ∼ 300 km/s.
   Since the discovery of RCS0224.5-
0002 we have found several other spec-
tacular multiple-arc strong lens clusters.
Of the total of 8 strong-lens systems, 2
more are comparable to RCS0224.5-
0002. This high proportion of multiple
arc systems argues that there must ex-
ist a class of “super-lenses” which, for
some yet undetermined reason, act as
particularly powerful lenses. Notably,
the strong lens clusters in the RCS are
all at z > 0.64, and it thus seems likely
that the source of this lensing boost is
associated with early times when clus-
ters are still forming, and that whatever
is responsible for the lensing boost            Figure 5: This 40 40 image is a colour composite of zI+R+BV images of RCS0224.5-0002.
evolves away as clusters age (Gladders          Various features – two candidate radial arcs, and excess blue light in the cluster centre – are
et al. 2003).                                   highlighted in grey-scale inserts. Arc C is at z = 4.8786. (Adapted from Gladders et al. 2002)

42
                                                                                                  servational plane, the measured quanti-
                                                                                                  ties are N(z,m) and the two-point corre-
                                                                                                  lation function, ξ(r,m).
                                                                                                     No clustering studies of small galaxy
                                                                                                  groups with m > 3 have been carried
                                                                                                  out, basically because of small survey
                                                                                                  area, bad number statistics and lack of
                                                                                                  deep homogeneous data. To find
                                                                                                  groups at different redshifts, deep wide
                                                                                                  field imaging is needed. In this project,
                                                                                                  SDSS and RCS provide the low and
                                                                                                  high-z groups, to z < 0.7 respectively. A
                                                                                                  number of groups have been detected
                                                                                                  on the RCS data. In order to measure
                                                                                                  the spatial clustering properties, inver-
                                                                                                  sion of 2-dimensional data is required.
                                                                                                  Currently, redshifts of group members
                                                                                                  selected from SDSS and RCS are being
                                                                                                  measured.

                                                                                                  References
                                                                                                  Gladders, M. D., & Yee, H. K. C. 2000, AJ,
Figure 6: Arc C in R band (left), I band (middle), and in Ly emission (right). The spectral im-     120, 2148
age has not been sky subtracted. The position of the slit as reconstructed after the FORS ob-     Gladders, M. D., Yee, H. K. C., & Ellingson
servations, is also indicated in the broadband images.(Adapted from Gladders et al. 2002)           E. 2002, AJ, 123, 1
                                                                                                  Gladders, M. D., Hoekstra, H., Yee, H. K. C.,
are fully characterized by their corre-          strong relation between the dark matter            Hall, P. H., & Barrientos, L. F. 2003, ApJ,
                                                                                                    in press
sponding halo dark matter mass. If so,           halo mass and the number of members              Franx, M., Illingworth, G. D., Kelson, D. D.,
how can observations be used to meas-            with similar luminosities in clusters,             van Dokkum, P. G., & Tran, K.-V. 1997,
ure the “bias” ? Theoretically, there is a       cluster number richness, m. In the ob-             ApJ, 486, L75



Long Period Variables in the Giant Elliptical
Galaxy NGC 5128: the Mira P–L Relation at 4 Mpc
M. REJKUBA1,2, D. MINNITI 2, D. R. SILVA1, T. R. BEDDING3
1
 ESO, Garching, Germany; 2Department of Astronomy, P. Universidad Católica, Chile; 3School of Physics,
University of Sydney, Australia

    In a stellar population older than a         (SRs). SRs usually have smaller ampli-           (CMDs) of two fields in the halo of this
few hundred Myr, the near-infrared light         tudes as well as shorter and more ir-            giant elliptical galaxy (Figure 1). These
is dominated by red giants. Among                regular or even multiple periods. They           CMDs show broad giant branches indi-
these, the stars lying on the red giant          are sometimes divided into subclasses            cating a large spread in metallicity. The
branch (RGB) are the brightest among             (SRa, SRb) depending on the regularity           RGB tip is detected at K ~ 21.3.
the metal poor stars older than 1– 2 Gyr.        and multiplicity of their periods and               A large number of sources are ob-
In intermediate-age populations (~ 1– 5          shape of their light curves. The separa-         served brighter than the tip of the RGB.
Gyr old) numerous bright asymptotic gi-          tion between Miras and SRs is not al-            These can belong to one of the three
ant branch (AGB) stars are located               ways very clear. The classical definition        categories: (i) intermediate-age AGB
above the tip of the RGB. However, also          requires that Miras have V-band ampli-           stars with abundances similar to those
among old populations like Galactic              tudes larger than 2.5 mag and regular            found in Magellanic Clouds, (ii) old and
globular clusters with [Fe/H] ≥ –1.0 and         periods in the range of 80–1000 days.            metal-rich AGB stars similar to those
in the Galactic bulge, bright stars have         Mean K-band amplitudes of Miras are              found in the Galactic Bulge and metal-
been detected above the tip of the RGB           typically 0.6 mag. SRs show more ir-             rich globular clusters, or (iii) blends of
implying the presence of bright AGB              regular variability, as their name indi-         two or more old first ascent giant branch
stars in metal-rich and old populations.         cates, and have smaller amplitudes.              stars. While Rejkuba et al. (2001) have
All of the bright giants above the RGB              So far, LPVs have been studied in the         shown with simulations that only a small
tip in globular clusters seem to be long         Milky Way, Magellanic Clouds and a few           part of these sources can be ascribed to
period variables (LPVs; Frogel & Elias           other Local Group galaxies. However,             blends, a definite proof that these bright
1988). Old populations of lower metal-           the Local Group lacks the important              red giants belong to the AGB population
licity are known not to have AGB stars           class of giant elliptical galaxies. At the       in NGC 5128 is through the detection of
brighter than the RGB tip.                       distance of about 4 Mpc (Harris et al.           variability of these sources. Further-
    Long period variables are thermally          1999), NGC 5128 (Centaurus A) is the             more, the near-IR properties of long pe-
pulsing asymptotic giant branch (TP-             closest giant elliptical galaxy, the clos-       riod AGB variable stars can be used to
AGB) stars with main sequence mass-              est active galactic nucleus (AGN), one           investigate the presence or absence of
es between 1 and 6 M . They have vari-           of the largest and closest radio sources         an intermediate-age component in the
ability with periods of 80 days or longer,       and a classical example of a recent              stellar populations of this giant elliptical
and often the longest period variables           merger. It is the dominant galaxy of the         galaxy. This has important conse-
show variable or multiple periods. Two           nearby Centaurus Group of galaxies.              quences for the formation and evolution
main classes of LPVs are Mira variables          Rejkuba et al. (2001) presented optical-         of giant elliptical galaxies.
(Miras) and semi-regular variables               near-IR colour-magnitude diagrams                   Using the multi-epoch K-band pho-

                                                                                                                                           43
tometry we investigated the nature of           frames obtained with short (60 sec) ex-          Field 2 have periodic variations. Of
bright giants observed above the tip of         posures that were dithered in an auto-           these, 536 and 878 had at least 10
the RGB (Figure 1) in two halo fields in        matic pattern in order to allow the sky          measurements with individual errors
NGC 5128. Field 1 is located in the             subtraction in this stellar field. Each of       smaller than 0.5 mag, and for these we
north-eastern halo of the galaxy and it         these 60-sec exposures was already an            constructed light curves.
coincides with the prominent diffuse            average of six 10-sec exposures. It is               A Fourier analysis of the K-band light
stellar shell, presumably a remnant             necessary to average a large number of           curves was used to search for the peri-
from a recent merger. Field 2 is in the         such very short exposures due to high            odic signal in the data. The period ob-
southern halo of the galaxy. The data           background emission of the sky in near-          tained from the frequency with largest
were taken in the K-band over three             IR wavelengths. The PSF fitting pho-             power corresponds to the most proba-
years with ISAAC at the VLT. As a result        tometry was done for each single-epoch           ble sinusoidal component. It was further
of this long term program, which re-            image individually. The final photomet-          improved with a non-linear least-square
quired repetitive observations of the           ric catalogue contains 13,111 stars in           fitting of the sine-wave. From this, the
same halo fields, we have discovered            Field 1 and 16,435 stars in Field 2,             best-fitting period (P), amplitude, mean
more than 1000 long period and large            which have been detected on at least 3           magnitude and phase were obtained. In
amplitude red variable stars confirming         K-band frames as well as in J and H-             optical passbands Miras often have
the presence of an AGB population in            band images.                                     asymmetric light curves, usually steeply
this giant elliptical galaxy halo.                 A combined colour image for Field 2           rising to the maximum and with a shal-
                                                of J, H and the best-seeing epoch in K-          lower decline. In the near-IR the varia-
ISAAC photometry                                band is shown in Figure 2. Figure 3              tions are more regular and nearly sinu-
                                                shows a small portion of this field, along       soidal. Hence a sine-wave is a good ap-
   We obtained a total of 20 epochs of          with five K-band epochs in which sever-          proximation to most of the LPVs.
K-band photometry in Field 1 and 24             al large amplitude stars can be seen.                For 99 variable stars in Field 1 and
epochs in Field 2 in the time interval be-      Most of these correspond to red                  169 in Field 2, no acceptable periods
tween April 1999 and July 2002. The             sources on the colour image.                     could be obtained because of the non-
data were obtained in service mode                                                               sinusoidal variations, large errors com-
with ISAAC at the VLT, except one Field         Long period variable stars                       bined with small amplitudes, multiple
2 epoch, which was secured on an ob-                                                             periods, presence of irregular period or
serving run in February 2000 with SOFI             Variable stars were identified using a        cycle-to-cycle variations typical for
at the NTT under exceptional seeing             procedure similar to the one described           Miras and semi-regular variables, or ab-
conditions. The exposure times for dif-         by Stetson (1996). First, we selected all        sence of period (e.g. microlensing,
ferent epochs varied due to changes in          the stars with mean photometric errors           background AGN or SN). In Figure 4,
seeing and sky conditions, but on aver-         given by ALLFRAME smaller than 0.2               we show a sample of good light curves
age one hour of observation was taken           mag. We then required each star to be            folded with the periods that are indicat-
per epoch for each field. The total ex-         detected on more than 5 frames and               ed in each panel. Note that each point
posure times amount to 19.7 and 21.1            constructed variability indices which            is plotted twice to emphasize the vari-
hours for Fields 1 and 2, respectively.         measure time-dependent correlation of            ability.
These are the deepest near-IR images            magnitude residuals. In other words,                 The mean amplitude of all the vari-
taken so far in the halo of an elliptical       given a mean magnitude and taking into           ables for which we could measure peri-
galaxy.                                         account photometric errors, variability          ods is 0.7 mag, and the majority have
   Data reduction included dark sub-            indices show how much a stellar bright-          periods in the range of 150 to 500 days.
traction, flat-fielding and sky subtrac-        ness varies between different observa-           With 24 or fewer measurements per
tion. For each epoch, a single image            tions. With these indices, we found that         star obtained over an interval of 1,197
was obtained combining individual               601 stars in Field 1 and 903 stars in            days, and with observations distributed
                                                                                                 in 3–6 month intervals interspaced by
                                                                                                 ~6 months gaps, there may be some
                                                                                                 period aliasing. However, most of the
                                                                                                 determined light curves are of good
                                                                                                 quality (see Figure 4). For some of the
                                                                                                 variables the best fitting periods were
                                                                                                 longer than 600 days and these need to
                                                                                                 be confirmed with observations over a
                                                                                                 longer time baseline. The amplitudes
                                                                                                 and periods of the LPVs are character-
                                                                                                 istic of Mira variables and are similar to
                                                                                                 those found in the LMC, SMC and
                                                                                                 Galactic Bulge. These are the most dis-
                                                                                                 tant Miras for which periods have been
                                                                                                 measured and the first in an elliptical
                                                                                                 galaxy.

                                                                                                 The NGC 5128 distance with the
                                                                                                 Mira P-L relation

                                                                                                    A well-defined period-luminosity (P-
                                                                                                 L) relation has been found for Miras in
                                                                                                 the Large Magellanic Cloud (Glass &
                                                                                                 Lloyd Evans 1981, Wood 1999), the
                                                                                                 Small Magellanic Cloud (Cioni et al.
Figure 1: Optical-infrared CMD for 5630 stars in the NGC 5128 shell field (F1; left) and 9001    2003), the Galactic Bulge (Glass et al.
stars in the NGC 5128 halo field (F2; right), based on ISAAC+FORS1 images of a region            1995), the solar neighbourhood (van
covering 2n5 × 2n5 (Rejkuba et al. 2001). A large number of stars brighter than the tip of the   Leeuwen et al. 1997) and in Galactic
RGB, K ≤ 21.3 (magenta dashed line), are LPVs.                                                   globular clusters (Feast et al. 2002).

44
The relation holds for both Mbol and MK.
Since Miras are very luminous, their
tight P-L relation makes them interest-
ing for distance determination to other
galaxies.
   Our data are not sufficient to discrim-
inate Mira from SR variables on the ba-
sis of the regularity of their light curves.
Hence, to select the most probable
Miras we made a selection on period
(2 < log P(d) < 2.6) and on amplitude
(0.5 mag < ∆K < 1.5 mag). The mean
magnitudes derived from the non-linear
sine-wave fit were corrected for extinc-
tion by subtracting AK = 0.039, corre-
sponding to E(B–V) = 0.11. The period-
luminosity diagram is displayed in
Figure 5. Field 1 variables are plotted
with blue and Field 2 variables with red
symbols. Variables with better deter-
mined periods based on the signifi-
cance parameter from Fourier fitting al-
gorithm are plotted with larger symbols.
   Most of these Mira variables are lo-
cated where expected, along a well
populated sequence in the P-L diagram.
This is the first time a Mira P-L relation
has been observed in a galaxy outside
the Local Group.
   Calibration of the P-L relation relies
on the LMC P-L relation for Miras. Feast
et al. (1989) fit to the LMC Mira P-L re-
lation is: MK = –3.47 log P + β. The zero
                                                     Figure 2: A combined color image for Field 2. The J-band is coded in blue, the H-band is
                                                  green and the K-band image is red. This field is located roughly 9n (corresponding to 10.5 kpc
  Figure 3: Zoom of a 131 × 131 pix (19 4 ×       at the distance of 4 Mpc) south of the centre of the galaxy. The total exposure time for each
19 4) region showing variable stars in Field 2.   band is 1 hour and the field of view is 2n.0 × 2n.07. North is up and east to the right. Note the
Most of the red stars are variable. There is a    large number of red sources – most of these are long period variable stars.
pair of stars in the centre of this field that
varies in counter-phase with similar periods.




                                                                                                                                               45
Figure 4: A sample of phased K-band light curves from both fields. Periods (P) are indicated in each panel. Each point is plotted twice to em-
phasize the variability.


Figure 5: Period-                                                                                vations. All the images were taken in ex-
Luminosity diagram                                                                               cellent seeing conditions, ranging from
in NGC 5128 for                                                                                  0 .35 – 0 .65, enabling us to detect vari-
long period (2 < log                                                                             able stars in a giant elliptical galaxy for
P(d) < 2.6) and                                                                                  the first time and construct the first Mira
large amplitude (0.5                                                                             period-luminosity diagram outside the
< ∆K < 1.5 mag)                                                                                  Local Group. The catalogue with light
variables. Large                                                                                 curve parameters and near-IR photom-
symbols are used                                                                                 etry of all the variable stars is available
for Miras with more                                                                              through Astronomy & Astrophysics
significant periods.                                                                             (Rejkuba et al. 2003).
Field 1 variables are
blue and Field 2 are                                                                             Acknowledgements
red. The black line
is our best fit to the                                                                             We are indebted to many ESO staff
Mira sequence. The                                                                               astronomers who took the data pre-
green line is the                                                                                sented in this paper in service mode op-
best fit to the Mira                                                                             erations at Paranal Observatory. DM is
sequence adopting                                                                                sponsored by FONDAP Center for
the slope of –3.47                                                                               Astrophysics 15010003.
(Feast et al. 1989).

                                                                                                 References
point β = 0.88 ± 0.10 has been recently           Conclusions
derived using Hipparcos parallaxes for                                                           Alves, D.R., Rejkuba, M., Minniti, D., Cook,
Miras in the solar neighbourhood and in              ISAAC multi-epoch K-band photome-             K.H., 2002, ApJ, 573, L51
well-studied Galactic globular clusters           try of two fields in the halo of NGC 5128      Cioni, M.-R.L., et al., 2003, A&A, in press,
(Feast et al. 2002). With such a calibra-         was used to detect variable stars. We            astro-ph/0304143
tion, the Large Magellanic Cloud dis-             derived periods for most of these vari-        Feast M.W., Glass, I.S., Whitelock, P.A.,
tance modulus is 18.60 ± 0.10.                    ables via Fourier analysis of the K-band         Catchpole, R.M., 1989, MNRAS, 241, 375
   A least-squares fit to the Mira se-            light curves and sine-wave fitting. Their      Feast M.W., Whitelock, P.A. & Menzies, J.,
quence in NGC 5128 is:                            magnitudes indicate that they are in the         2002, MNRAS, 329, L7
                                                                                                 Frogel, J.A. & Elias, J.H., 1988, ApJ, 324,
   K0 = – 3.36 (± 0.13) log P + 28.81 (± 0.32).   AGB phase and their periods and am-              823
This fit is overplotted as a solid black          plitudes are consistent with being LPVs.       Glass, I.S., Lloyd Evans, T., 1981, Nature,
line in Figure 5. The 1σ scatter around              The long-period (400 ≥ P ≥ 100 d)             291, 303
the fit is 0.19. Fixing the slope to be           large-amplitude (0.5 < ∆K < 1.5 mag)           Glass, I.S., Whitelock, P.A., Catchpole, R.M.,
–3.47, the best fitting zero point is 29.09       Mira variables were used to determine            Feast, M.W. 1995, MNRAS, 273, 383
± 0.32 (solid green line in Figure 5), with       the distance of NGC 5128 from a P-L            Harris, G.L.H., Harris, W.E. & Poole, G.B.,
the same RMS of the fit.                          relation. Adopting a LMC distance mod-           1999, AJ, 117, 855
   Finally, the derived distance modulus          ulus of 18.50, we derive the distance          Rejkuba, M., Minniti, D., Silva, D.R. &
to NGC 5128 is 28.21 ± 0.32, assuming             modulus of 28.1 ± 0.3, corresponding to          Bedding, T., 2001, A&A, 379, 781
                                                                                                 Rejkuba, M., Minniti, D. & Silva, D.R., 2003,
a LMC distance modulus of 18.60. If               D = 4.2 ± 0.6 Mpc.                               A&A, in press
18.5 is preferred (e.g. Alves et al. 2002),          In closing, we would like to note that      Stetson, P.B., 1996, PASP, 108, 851
the distance modulus to NGC 5128                  such programs that require numerous            van Leeuwen, F., Feast, M.W., Whitelock,
would be 28.11 ± 0.32, in good agree-             (>10) and relatively short (~ 1.5 h per          P.A., Yudin, B., 1997, MNRAS, 287, 955
ment with that derived from the RGB tip           Field) observations benefit greatly from       Wood, P. R. et al. 1999, in IAU Symp. 191:
(Harris et al. 1999).                             the availability of service mode obser-          Asymptotic Giant Branch Stars, p. 151


46
The Dynamics of Dwarf Elliptical Galaxies
H. DEJONGHE1 , S. DE RIJCKE1, W. W. ZEILINGER 2, G. K. T. HAU 3
1
 Sterrenkundig Observatorium, Ghent University, Belgium;
2
 Institut für Astronomie, University of Vienna, Austria; 3ESO, Santiago, Chile

A short history                                 the VLT, do astronomers have the pos-           formation is enhanced at larger radii,
    Dwarf elliptical galaxies (dEs) are         sibility to obtain spectroscopic informa-       dEs are more diffuse than Es (which
small diffuse galaxies with smooth ellip-       tion out to large radii, opening up the         have higher escape velocities and hold
tical isophotes. One of the most nearby         study of the spatial variations of the stel-    on to their gas more strongly) and have
examples is NGC 205 (M110), a satel-            lar populations and the determination of        higher metallicities at larger radii, ex-
lite of the Andromeda galaxy. From the          the orbital structure and dark matter           plaining the observed outward redden-
days of the great comet-hunter Charles          content of dEs.                                 ing of dEs. Since the stars are born out
Messier up to well into the 20th century,                                                       of gas that is moving outwards, the or-
this was the only known object of the           Models for dE Evolution                         bital distribution of the stars will favor
class that we now call dEs. In 1944,                 Although similar to normal ellipticals     radial orbits and rotation will be slow.
Walter Baade confirmed NGC 147 and               (Es) at first sight, dEs are quite different   There is a problem with this model how-
NGC 185 as members of the Local                  from their larger brethren. To begin with,     ever: standard cosmological models
Group by resolving them into individual          dEs are much more diffuse objects with         predict that small density fluctuations
stars, a feat which was only possible            exponentially declining surface-bright-        are less clustered than larger ones,
because these dEs are very nearby                ness profiles (Es on the contrary are          from which the Es grow, contrary to the
galaxies. No new Local Group dEs have            well described by the more centrally           observed clustering properties of dEs.
been discovered since then. In the               concentrated de Vaucouleurs law).                  The harassment model explicitly
1950s, dEs were also discovered in the           Moreover, and again contrary to Es,            takes into account the fact that dEs are
nearby Fornax and Virgo clusters, offer-         dEs become noticeably redder towards           very clustered objects. N-body simula-
ing the possibility to study their photo-        larger radii. Current paradigm has it that     tions have shown how a late-type (Sc-
metric properties on larger samples: a           star-formation proceeded most vigor-           Sd) disc galaxy that orbits in a cluster or
dE is a rather gregarious species, spot-         ously in the dense centres of Es, lead-        around a massive galaxy can be desta-
ted abundantly in dense environments             ing to a central population of metal-rich      bilized by gravitational interactions. The
such as clusters and groups of galaxies.         stars. These have many strong absorp-          small disc galaxy develops a bar that
Spectroscopy of such low-surface-                tion lines in the blue part of the spec-       transports angular momentum to the
brightness galaxies is challenging how-          trum and thus make the centres of Es           halo and to stars at larger radii which
ever, and had to wait until the early            appear reddish. Finally, up to recent          are lost as tidal tails. Gas is funneled in
1990s. At that time, 4 m-class tele-             times, most of the dEs for which kine-         towards the centre by torques exerted
scopes, CCD cameras, in combination              matic information was available turned         by the bar where it is converted into
with long exposure times, could start to         out to rotate very slowly if at all. This      stars, forming a nucleus. The originally
explore the kinematics and stellar pop-          sets them apart from the low-luminosity        rotationally flattened disc galaxy is heat-
ulations of the central regions. Only now        Es that are generally fast-rotating ob-        ed and transformed into an anisotropic,
however, with large telescopes such as           jects. This is the so-called “kinematic di-    slower rotating dE. The way a dwarf
                                                                 chotomy” between Es and        galaxy is affected depends on its orbit
                                                                 dEs. Wrapping this up, the     and some dEs may still contain some
                                                                 photometric and kinematic      memory of their disky origin. Thus,
                                                                 differences between dEs        these simulations not only offer a natu-
                                                                 and Es make it unlikely        ral explanation for the clustering prop-
                                                                 that ellipticals and dEs       erties of dEs and the central luminosity
                                                                 share a common origin or       spike (or “nucleus”) observed in many
                                                                 a similar evolution. Two       bright dEs, but they also accomodate a
                                                                 currently popular models       number of recently discovered key ob-
                                                                 attempt to explain the         servational facts: the existence of fast-
                                                                 properties of dEs (see         rotating dwarfs, dEs that still contain
                                                                 Figure 1).                     gas and dEs with an embedded stellar
                                                                    According to the wind       disc.
                                                                 model, dEs are primordial
                                                                 objects that formed from       An ESO Large Programme
                                                                 average-amplitude cos-
                                                                 mological density fluctua-        We embarked on a Large Program-
                                                                 tions. Supernova explo-        me to obtain deep, high resolution spec-
                                                                 sions heat the interstellar    tra along the major and minor axis from
                                                                 medium (ISM) to velocities     a varied and sizeable sample of group
Figure 1: dE formation scenarios. Top : the wind-model. exceeding the galaxy’s es-              and cluster dEs to study their internal
Supernovae blow away a dense gas shell (blue arrows) in cape velocity and cause a               dynamics and stellar populations. The
which new stars are born. Subsequent supernovae further supersonic outflow of gas               goals of this program are (1) to assem-
accelerate the shell and enrich it with metals. Bottom : the from the galaxy, blowing           ble a large, homogeneous data-set of
harassment scenario. A dE is initially a fast rotating (green away most, if not all, of the     photometry, kinematics and dynamics
arrows) small disc galaxy, destabilized by gravitational inter- ISM. Stars form in this ex-     of dEs of unprecedented high quality,
actions. A bar develops and the disc is vertically heated. panding shell and subse-             (2) to model the dynamics of dEs rang-
After a new equilibrium has been reached, the galaxy has a quent supernova explo-               ing from dE0 to dE6, including dS0s, to
much rounder shape and slower (but still significant) rota- sions further accelerate its        check whether the kinematic dichotomy
tion. Some relics of its previous state, e.g. a stellar disc, expansion and enrich it           between Es and dEs is real and
might survive the turmoil.                                       with metals. Since star-       whether dEs become more rotationally

                                                                                                                                       47
                                             these emission lines. Finally, the spec-       estimates of their masses and mass-to-
                                             tra were flux-calibrated and co-added.         light ratios to be made.
                                                In the following, we will discuss the
                                             extraction of kinematic information from       FS76, a rotationally flattened dE
                                             galaxy spectra and our dynamical mod-             The non-nucleated NGC5044-Group
                                             eling method, and present our results          dE1 FS76 (MB=–16.70 for H0=75
                                             so far (De Rijcke et al. 2001, 2003a,          km/s/Mpc) is a case study of a rotation-
                                             2003b).                                        ally flattened dE (De Rijcke et al. 2001).
                                                                                            Our observations were carried out in
                                             Determining kinematics                         May, 2000 with FORS2 on Kueyen.
                                                The absorption lines in a galaxy            Total integration time was 5 h for each
                                             spectrum are Doppler broadened due to          position angle. The analysis of the sur-
                                             the motions of the stars along the line of     face photometry confirms the picture of
                                             sight and their precise shape depends          FS76 as a normal dwarf elliptical (see
                                             on the line-of-sight velocity distribution     Figure 2). No photometric peculiarities
                                             (LOSVD) of the stars. The LOSVD is             were noted: there is only a modest
Figure 2: A VRI color composite image of     approximated as a fourth-order Gauss-          amount of isophote twist; also no signif-
FS76, a NGC5044-Group dE1. North is up,      Hermite series, condensing the kine-           icant deviations from ellipses were de-
east is to the left.                         matic information to the mean velocity         tected in the isophotes. Its heliocentric
                                             vp, the velocity dispersion σp and two         velocity, derived from the spectra, con-
supported as one goes to more flat-          coefficients, h3 and h4, that quantify re-     firms FS76 as a member of the
tened specimens, (3) to check the rela-      spectively asymmetric and symmetric            NGC5044 group.
tion between the mass-to-light ratio and     deviations from a Gaussian LOSVD.                 The central velocity dispersion σp
luminosity predicted by the wind model       These kinematic parameters can be ob-          equals 46 ± 2 km/s. The maximum rota-
and whether a cuspy dark-matter densi-       tained by fitting a weighted sum of stel-      tion velocity along the major axis is 15 ±
ty is required to fit the kinematic data     lar spectra, broadened with a parame-          6 km/s. The asymmetry in the mean ve-
(thus, dynamical models serve as a           terized LOSVD, to a galaxy spectrum.           locity and velocity dispersion profiles
check on CDM cosmological models of          Doing this for each row of the galaxy          (see Figure 3) may signal that FS76 is
galaxy formation), (4) search for dEs        spectrum yields the kinematics as a            currently undergoing an interaction with
with peculiarities such as embedded          function of position along the slit.           NGC5044 which is at a projected dis-
discs, fast rotation, ionised gas, kine-                                                    tance of only 30 kpc. The ratio of the
matically decoupled cores... that would      Dynamical modeling                             mean velocity vp to the velocity disper-
support the harassment scenario, (5)             Kinematics along major and minor           sion σp can be used as an indicator for
measure line-strengths in the wave-          axis can be used to constrain the dy-          the importance of rotation in the flatten-
length region λλ790–930 nm in order to       namics of a galaxy. A dynamical model          ing of a stellar system. For an isotropic
study the stellar populations of the sam-    consists of a gravitational potential and      E1 galaxy, flattened by rotation, one ex-
ple dEs.                                     a distribution function. The potential         pects vp/σp = 0.35. The observed ratio
   We used FORS2, equipped with the          generates the gravitational forces that        of the peak velocity to the central veloc-
very efficient volume phased holo-           bind the stars together, including the ef-     ity dispersion is (vp/σp)obs = 0.33 ± 0.15,
graphic grating GRIS_1028z+29. This          fects of the dark matter. The distribution     fully consistent with FS76 being an
combination gives both a high through-       function gives the number of stars on          isotropic oblate rotator. Moreover, the
put and high spectral resolution (σinstr =   each orbit. From these two ingredients,        best fitting dynamical model shows that
30 km/s with a 0.70 wide slit), allowing     all properties of a model can be calcu-        the radial velocity dispersion varies only
us to accurately measure velocity dis-       lated and compared to the observa-             by a few km/s from the equatorial plane
persions as low as 20 km/s, which we         tions. With our modeling technique,            towards the rotation axis and therefore
verified by extensive Monte Carlo simu-      three-integral axisymmetric models are         pressure differences play only a minor
lations. The exposure times were fine-       fitted to the kinematics. Since each           role in flattening this galaxy. Thus, the
tuned so as to reach 1.5–2 Re with a         model is given an absolute likelihood, a       observed kinematics and detailed dy-
signal to noise ratio S/N ≈ 15 per bin for   range of mass distributions that are           namical models unambiguously show
the brightest dEs of our sample              compatible to the data at a given confi-       that FS76 is indeed flattened by rotation
(15 < mB < 16). For fainter objects          dence level can be determined for each         and not by pressure. Since these find-
(mB ≥ 16.5), we go out to 1–1.5 Re at the    galaxy. This gives us detailed informa-        ings were published, more dEs with sig-
same noise level. The standard data re-      tion about the orbital structures of the       nificant rotation have been discovered,
duction procedures were performed            observed galaxies and allows robust            both by us and by others. These results
with ESO-MIDAS. The individual spec-
tra were bias-subtracted and flat-field-
ed. Cosmic ray events were removed
and the spectra were binned to a linear
wavelength scale (rectifying the emis-
sion lines of the arc spectra to an accu-
racy of 1 km/s FWHM). The sky back-
ground was subtracted very carefully.
Using blank sky-spectra we corrected
the spectra for variations of the slit-
transfer function which resulted in a per-
fectly flat sky background that could be
removed very accurately. The ubiqui-
tous bright OH Meinel emission bands
are undersampled at the high spectral
resolution we are working at and proved
much harder to remove completely.            Figure 3: The major-axis kinematics of FS76. Left: mean velocity vp and velocity dispersion
Fortunately, only a few galaxies had         σp. Right: Gauss-Hermite coefficients h3 and h4, quantifying asymmetric and symmetric de-
absorption lines that were affected by       viations from a Gaussian line-of-sight velocity distribution.


48
corroborate the prediction of the ha-
rassment scenario that fast-rotating dEs
should exist.

dEs with embedded discs
    We collected R and I band images of
FCC204 (dE6, MB=–16.52) and
FCC288 (dE7, MB=–16.18), two Fornax
cluster dEs, with FORS2 on Kueyen in
November, 2000 (De Rijcke et al.
2003b). Both galaxies have “disky”
isophotes, so they are better classified
as dwarf lenticular galaxies or dS0s. To
check whether this diskiness is caused
by the presence of a real stellar disc, we
applied an unsharp masking technique.
We smoothed the R-band image of
each galaxy with the MIDAS command
filter/med to replace each pixel by the
median of a 6 × 6 surrounding box.            Figure 4: Left panel : 120 sec. R-band image of FCC204. Right panel : result of unsharp
This smoothed image is then subtract-         masking. At the outer edges of the disc, two brightness peaks are visible (marked by arrows).
ed off the original one, highlighting any     North is up, east is to the left.
fine structure. The original and residual
images are presented in Figures 4 and 5.
    The prominent disc in FCC288 can
be traced out to 2 kpc. Clearly visible is
the flaring and warping of the disc. The
thickness of the disc remains more or
less constant around 160 pc inside the
inner kpc. Beyond that the disc thickens
rapidly, reaching ≈ 500 pc at a radial dis-
tance of 2 kpc. FCC204 has a much
less impressive disc, traceable to about
1.8 kpc and about 255 pc thick. Besides
a large bulge, two brightness maxima at
symmetric positions with respect to the
nucleus are visible. A possible interpre-
tation is that we are looking edge-on
onto a bulge+bar system and that the
two brightness enhancements consti-
tute the edges of the bar or perhaps are
even small spiral arms.                       Figure 5: Left panel: 600 sec. R-band image of FCC288. Right panel: result of unsharp mask-
    Spectra of FCC288 and FCC204              ing. The disc embedded in FCC288 runs practically across the whole face of the galaxy. The
were obtained with FORS2 in Novem-            flaring of the disc and the brightness fluctuations in it (marked by arrows), which could be spi-
ber, 2000 on Kueyen and November,             ral arms, are clearly visible. North is up, east is to the left.
2001 on Yepun, respectively. As an ex-
ample, the major axis kinematics of
FCC204 are plotted in Figure 6. Both
galaxies are very rapid rotators. Still,
they do not rotate fast enough to explain
their apparent flattenings. This is most
likely due to the fact that the observed
kinematics also reflect the motions of
the stars that make up the less flattened
(i.e. slower rotating, more anisotropic)
body of the galaxy. Inside the bulge of
FCC204, the LOSVDs have a Gaussian
shape. In the discs of both galaxies, the
LOSVDs are more peaked and skewed.
The edges of what we interpret to be a
bar in FCC204 correspond to changes
in the velocity dispersion and the rota-
                                              Figure 6: Major axis kinematics of FCC204. Left: mean velocity vp and velocity dispersion σp.
tion velocity. The very fast rotation and
                                              Right: Gauss-Hermite coefficients h3 and h4, quantifying asymmetric and symmetric devia-
the correlation of the various kinematic
                                              tions from a Gaussian line-of-sight velocity distribution.
parameters with the photometric fea-
tures strengthen our interpretation
based on the unsharp masking : both           dEs with a warm ISM                               Fornax cluster in November 2000 and
galaxies are seen practically edge-on           We obtained B, R, and I broad-band              November 2001. FCC046 was classi-
and contain fast-rotating disc struc-         images, Hα+[NII] narrow-band images               fied as a non-nucleated dE4 so the
tures. Such embedded stellar discs may        and spectroscopy of the nucleated dEs             presence of its very bright and blue nu-
be relics from the pre-harassment era,        FCC046 (dE4N, MB=–15.29) and                      cleus came as a surprise. The nucleus
according to the harassment scenario.         FCC207 (dE2N, MB=–15.09) in the                   is resolved under seeing conditions of


                                                                                                                                           49
                                                                                                        Figure 7: Left panel : a BRI
                                                                                                        colour composite image of
                                                                                                        FCC046. Note the off-centre
                                                                                                        nucleus. North is up, east is to
                                                                                                        the left. Right panel : Hα+[NII]
                                                                                                        emission image of FCC046.
                                                                                                        Six emission clouds other than
                                                                                                        the nucleus can be discerned.
                                                                                                        The horizontal bar measures
                                                                                                        5 on the sky. The inset shows
                                                                                                        a cut through the central emis-
                                                                                                        sion region. The intensity is
                                                                                                        plotted in units of
                                                                                                        W/m2/arcsec2.




0.8 FWHM and is offset by 1.1 to the           extinction using the R band extinction      six clouds observed in FCC046 (super-
south-west of the centre of the outer          coefficient and interstellar extinction.    nova remants, Wolf-Rayet nebulae) can
isophotes. It has a blue magnitude mB =        The emission-images were converted          be interpreted as unambiguous evi-
18.55 mag (MB=–12.77) and comprises            to physical units (W/m2) with the aid of    dence for recent or ongoing star-forma-
about 10% of the total B-band luminos-         the spectrum of a flux-calibration stan-    tion.
ity of the galaxy. FCC046 shows a pro-         dard star.
nounced lopsided shape. Given that                 Color images and pure Hα+[NII]          Preliminary conclusions
FCC046 is an isolated galaxy in the out-       emission images of FCC046 are pre-
skirts of the Fornax cluster, it is unlikely   sented in Figure 7. The total emission         In the course of this Large Program,
that an encounter caused this asymme-          luminosity of FCC046 is Lem(FCC046) =       we have assembled kinematics of un-
try. Based on broad-band colours, its          6 ×1030 W, about half of which is emit-     precedented high quality of a sample of
disturbed shape and its very bright nu-        ted by the central peak corresponding       15 dEs. All data have been reduced and
cleus, FCC046 is akin to the class of          to the galaxy’s nucleus. The total emis-    analysed, and the last few objects are
amorphous dwarfs, the name coined by           sion luminosity of FCC207 is somewhat       being modelled. Outstanding results
Allan Sandage for dwarf galaxies that          higher: Lem(FCC207) = 8 ×1030 W. The        based on selected objects have been
have a disturbed appearance due to re-         total mass in ionised hydrogen can be       published or are in press. More papers,
cent star formation and the presence of        estimated assuming complete re-ab-          in which we will present our conclusions
dust but are not irregular enough to be        sorption of all Lyman photons and an        based on the photometry, dynamics,
classified as Im (Magellanic-Cloud type        electron density Ne = 1000 cm–3. We         and line-strengths of the full sample, will
irregulars). The nucleus of FCC207 has         then find that for FCC046 MHII ≈ 40–150     be submitted shortly.
a distorted shape: it is more elongated        M and for FCC207 MHII ≈ 60–190 M ,             Thanks to the high spatial and spec-
than the bulk of the galaxy (E3 versus         depending on the unknown contribution       tral resolution of our observations, we
E2) and is somewhat kidney-shaped.             of the [NII] lines to the Hα+[NII] emis-    have uncovered the existence of dEs
This is probably due to dust-absorption        sion.                                       with complex behavior and internal
to the north of the nucleus, noticeable in         In FCC046, the emission is distrib-     structures (such as embedded stellar
the B-R color map. The B-R, B-I colors         uted over a bright central region and six   discs) that are hard to fit into a simple
stay essentially constant outside the          fainter clouds, three of which are re-      scenario in which dEs form through the
nucleus. Based on published UBV col-           solved. The diameters and luminosities      collapse of primordial density fluctua-
ors and metallicities, it was concluded        of the resolved clouds are consistent       tions, like the wind model. Clearly, dEs
that FCC207 is too blue in U-B (U-B =          with them being supernova-remnants          are anything but small “island univers-
0.15) and too metal-poor for its B-V (B-       but they are about 10 times larger than     es” that evolve in splendid isolation:
V = 0.78) and this was interpreted as a        HII regions of comparable luminosity.       their evolution appears determined, at
consequence of the presence of a               Nebulae around Wolf-Rayet stars could       least in part, by their environment.
young stellar population. This motivated       be a plausible alternative and are found    Thus, the harassment scenario offers
us to investigate both objects more            in many irregulars and have appropriate     an attractive explanation for many ob-
closely.                                       luminosities and diameters. The similar-    served features that are hard to explain
   We took 20 minute exposures of              ities of the broad-band colours of          with the wind model.
FCC046 and FCC207 with the                     FCC046 to those of star-forming or
Hα/2500+60 narrow-band filter with             amorphous dwarfs, its relatively strong     References
FORS2 on Yepun. R band images                  core and the presence of emission
served as off-band images. The narrow-         clouds support the conclusion that          De Rijcke S., Dejonghe H., Zeilinger W. W.,
band filter only lets through the light of     FCC046 is actively forming stars, albeit      Hau G. K. T., 2001, ApJL, 559, L21-L24
the Hα 6563 Å emission line of ionised         at a very leasurely pace when com-          De Rijcke S., Zeilinger W. W., Dejonghe H.,
hydrogen and two adjacent emission             pared to Blue Compact Dwarfs (BCDs)           Hau G. K. T., 2003, MNRAS, 339, 225-234
                                               and amorphous dwarfs which are about        De Rijcke S., Dejonghe H., Zeilinger W. W.,
lines of ionised nitrogen, [NII] 6548,
                                               a factor 1000 more luminous in Hα. The        Hau G. K. T., 2003, A&A, 400, 119-125
6583 Å and thus traces the presence of                                                     Ferguson H. C., Binggeli B., A&ARv, 6, 67-
ionised gas. The standard data reduc-          nuclear emission of FCC046 and                122
tion procedures (bias subtraction, flat-       FCC207 can be adequately accounted          Moore B., Katz N, Lake G., Dressler A.,
fielding, cosmic removal, interpolation        for by photo-ionisation by post-AGB           Oemler Jr. A., Nature, 379, 613-616
over bad pixels, sky subtraction) were         stars although a contribution of Hα         Mori M., Yoshii Y., Tsujimoto T., Nomoto K.,
performed with MIDAS. All science im-          emission from star-formation cannot be        ApJL, 478, L21-L24
ages were corrected for atmospheric            excluded. Only the emission from the        Simien F., Prugniel P., A&A, 384, 371-382

50
                  OTHER ASTRONOMICAL NEWS
From Books to Bytes:
Changes in the ESO Libraries over the Past Decade
UTA GROTHKOPF, ESO Library Garching, esolib@eso.org
   Ten years in the lifetime of an astron-    portunities for discussion about library      lisher, trying to achieve the best possi-
omy library may not be much, but the          matters and for suggestions and com-          ble conditions for our users. Some elec-
past decade brought many changes,             ments.                                        tronic journals were not subscribed be-
and it may be worthwhile to pause for a                                                     cause of unacceptable usage condi-
moment and look back. Ten years ago,          The Mid-90s: Electronic Journals              tions or outrageous prices. During these
we spent most of our time doing paper                                                       years, communication and networking
work, dealing with incoming invoices             The Internet revolutionized communi-       among astronomy librarians was invalu-
and processing new books. Our tasks           cation and information access. In order       able. In 1988 the first conference on
centred on the publications physically        to bring the library holdings to the as-      Library and Information Services in
located in the libraries.                     tronomers’ desktops, our catalogue be-        Astronomy (LISA) was held, and there
   Today, the physical library sites have     came available online in 1992. At that        was a strong wish among the communi-
decreased in importance, and the virtu-       time, access was via a non-graphical          ty for another meeting. LISA II took
al library is about to take their place.      telnet interface that was replaced in         place at ESO Garching in 1995; it pro-
The Internet has become the essential         1996 by a more user-friendly web cata-        vided an excellent opportunity for dis-
tool to retrieve information and provide      logue. A paradigm shift in information        cussion about the changing world of li-
rapid service to our users. Instead of        retrieval occurred in the mid-nineties        braries not only among librarians, but
making publications available in the li-      with the advent of electronic publica-        also with participating astronomers,
brary, it has become more important to        tions. They opened a whole new world          publishers and computer specialists.
provide access through the library so         of challenges as well as concerns (see           With the growing acceptance of the
that astronomers can reach them con-          Table 1, top). Archiving electronic docu-     arXiv.org (astro-ph) e-print server since
veniently from their desktops.                ments became one of the most heated-          1996, preprints were undergoing major
                                              ly discussed topics among librarians. E-      changes. Electronic preprints allowed
The Early 90s: Focus on the                   publications cannot be stored once for        astronomers to distribute research re-
In-House Library Collection                   good like paper documents, assuming           sults long before publication in journals,
                                              that they will always be usable as they       and observatories, in order to save on
    During the early nineties, ESO main-      were at the time of their creation.           shipping costs, considered switching
tained libraries in Garching and at La        Technology is changing rapidly; micro-        from paper to electronic format. This
Silla as well as a smaller third library in   film, microfiche, and the 5.25 diskette       trend became obvious in our libraries
La Serena. The main focus of our at-          remind us how quickly storage media           when we started to receive lists of titles
tention was on the resources physically       and the corresponding reading devices         and authors instead of the actual
available in the ESO libraries. Book ac-      can become obsolete. In the early days        preprints. Later, even these were sub-
quisitions, journal issue check-in and        of electronic publications, various           stituted by pointers to the institutes’ web
other technical tasks demanded a large        archiving models were considered,             pages where preprints were made
amount of time. After payment, all pur-       ranging from off-line storage on CD-          available. It was a logical consequence
chased items belonged to the library.         ROMs to simply discarding archives af-        to provide access to these web sites
The concept of “fair use” allowed us to       ter some years. To date, a definitive so-     from our library pages. For the ESO li-
photocopy journal articles for personal       lution is still pending.                      braries, the World Wide Web has al-
and research purposes as well as to              We have spent a lot of time under-         ways been an attractive way of provid-
send them to requesting libraries             standing, reviewing, and negotiating li-      ing information. Already in the early
through inter-library loan. This assured      cense agreements for electronic jour-         nineties, we began to explore its oppor-
(almost) equal and fair access to the         nals. Previously, copyright had deter-        tunities, and the library homepage was
scientific literature for researchers from    mined for which purposes publications         among the first at ESO. Since then, the
rich and less fortunate institutes alike.     could be used, but these regulations          content and layout have undergone
Continued access to the astronomical          were not extended to the electronic en-       several changes, and the number of
literature was guaranteed because li-         vironment. Instead, contracts had to be       pages has grown considerably. In par-
braries archived publications of long-        signed which often reduced user rights        ticular for new users, the homepage of-
lasting interest.                             and left questions, in particular regard-     ten is the first point of contact with the li-
    Newsletters and reports from obser-       ing future access. What will happen if        brary (www.eso.org/libraries/).
vatories around the world brought infor-      subscriptions end? Will we be allowed            In 1994, the La Serena library was
mation about ongoing projects to the          to access the volumes we already paid         transferred to La Silla, the one at La
astronomers’ attention. Occasionally,         for after cancellation, or will we lose ac-   Silla, in turn, moved to the Vitacura of-
ESO scientists and engineers needed           cess to back issues? Will archives be         fices in Santiago. From that time on-
articles and books that were not avail-       maintained if a journal ceases publica-       wards, the La Silla library was unstaffed
able at ESO. Document delivery servic-        tion or a publisher is sold to another        except for occasional visits by the li-
es were not yet in place, and obtaining       company? Like many other observatory          brarian. In the course of the years, its
publications from other libraries was a       libraries, ESO does not belong to a uni-      usage decreased, and book purchases
time-intensive process.                       versity system where contracts are ne-        were slowly reduced to reflect the
    Many astronomers stopped by the li-       gotiated and signed by the central li-        changed user behaviour. Rising journal
brary regularly to look at new journal is-    brary for all affiliated branch libraries.    subscription costs, partly resulting from
sues, preprints and latest book acquisi-      This means that we have had to discuss        considerable extra fees for electronic
tions. Their visits provided ample op-        any amendment directly with the pub-          access charged by some publishers,


                                                                                                                                      51
were a constant matter of concern. In
1999, cancellations of less frequently
                                                                             Early 90s                         2000+
used journals became necessary. This           Print versus Electronic Publications
marked the beginning of a change from          Format                        Print documents                   Electronic (networked) documents
purchasing publications “just in case” to      Material location             Library                           Publishers’ servers
“just in time” – documents were no             Usage rules                   Copyright                         Contracts
longer obtained because someone may            Purchase concept              Library owns                      Access only for duration
                                                                             purchased publications            of contract
eventually be interested, but only when
they were actually requested. It was our       Archiving                     Done by libraries                 To be determined
responsibility to find the most cost-ef-       Information Retrieval and Provision
fective and efficient solution for each        Information access            Locally in the library            From anywhere, at any time
publication.                                   Information resources         On paper                          Interconnected databases; non-
                                                                                                               electronic resources become
2000 Onwards: Virtual Libraries                                                                                marginalised
                                               Library visibility            Users are aware of the library    Users bypass the physical library;
                                                                             and its services                  library role becomes invisible
   Despite the increasing availability of
electronic documents, print publications
continue to arrive in our libraries as be-                                              Past and present
fore. Up to now, electronic format hasn’t      Library Mission and Role
replaced paper, but complements it. For
                                               Mission statement             Fulfill the information needs of our users by selecting, collecting,
most journals the print edition is still re-                                 preserving, and providing access to relevant resources
garded as the reference version, and           Tools                         Monitor, evaluate and, if appropriate, apply available information
astronomy books are not even available                                       retrieval tools
yet in electronic format. Traditional li-      Interaction with users        Tailor library services according to the specific needs of users
brary tasks like bookbinding, journal          Mediation                     Learn about requirements of library users; use results for service
check-in, and book processing still de-                                      enhancement within the library and as feedback to publishers
mand their share of time. On the other
hand, it is obvious that collection devel-     Table 1: What has changed and what hasn’t: Library functions and role in the past decade.
opment in the digital age takes on a new
face. The notion of all purchased publi-       creased by a factor of almost 2.6. Some          where, at any time through the Internet,
cations being physically located within        questions remain though: How will as-            and they often bypass the library in their
the four walls of our libraries has            tronomers cope with this approach in the         search for information. Our role in pro-
ceased to exist. Electronic books, once        long run? Will increased demand for elec-        viding access to information resources
they are of importance in astronomy,           tronic format result in even higher prices       has become invisible; many of the tasks
will have to be integrated into our cata-      for e-journals? Will print-only resources        we accomplish are not immediately no-
logue. Bibliographic records of electron-      be neglected completely in future?               ticed by the users, or are not attributed
ic journals already contain hyperlinks to         During recent years, the library has          to libraries. The question may arise: do
journal homepages so that users can            become involved in bibliometric studies          we still need libraries? The answer can
access them seamlessly from the web-           to measure scientific return from tele-          be illustrated by an anecdote that dates
cat. In 2002, ESO Management decid-            scopes. Since the early nineties, we             from the time of LISA II. During program
ed to establish an electronic-only library     have compiled the bibliography of pa-            preparations, one of the organizers (not
at the VLT telescope site at Paranal.          pers by ESO staff and visitors. While its        a librarian) suggested to change the full
The number of books purchased for              initial purpose was to provide a com-            name of the conference to Library and
Paranal will be kept at the very mini-         plete list of publications for the ESO           Information Systems in Astronomy, but
mum and journals will be available in          Annual Report, it has matured into a             the librarians insisted that the S stands
electronic format only. Also for the La        database on the use of ESO telescope             for Service, and the original name re-
Silla library, the emphasis will be on         data in refereed journal articles, includ-       mained unaltered. Personalized service,
electronic access from now on. As a first      ing information on the instruments used          tailored to the individual needs of the li-
step, existing print subscriptions includ-     for observations as well as observing            brary users, distinguishes libraries from
ing core astronomy journals were               programme IDs. These data may be                 software tools. The “human factor” re-
stopped for La Silla. The trend seems to       linked to the AVO (Astrophysical Virtual         mains important also in the digital age,
be clear: astronomers retrieve publica-        Observatory) databases in the future.            be it for “troubleshooting” if things go
tions electronically and print them local-        The electronic age has been upon us           wrong or for tricky cases of information
ly. Figure 1 shows the number of ApJ,          for several years now. Astronomers               retrieval for which users appreciate as-
AJ and PASP article downloads from             have become used to interconnected               sistance. Although many changes have
2000 to 2002; the total number in-             resources being available from any-              occurred in library management and in-
                                                                                                formation provision during the past
                                                                                                years, the library’s mission and role are
                                                                                                still the same (Table 1): we fulfil the in-
                                                                                                formation needs of our users by select-
                                                                                                ing, collecting, preserving, and providing
                                                                                                access to relevant resources. We moni-
                                                                                                tor, evaluate and, if appropriate, apply
                                                                                                available information retrieval tools. By
                                                                                                communicating with library users, we
                                                                                                learn about their requirements and use
                                                                                                the results for service enhancement
                                                                                                within the library and as feedback to pub-
                                                                        Figure 1: Article       lishers and information providers. In this
                                                                        downloads from          way, we sustain the traditional library
                                                                        major astrono-          functions and at the same time respond
                                                                        my     journals,        to the changes that occur in the way as-
                                                                        2000 – 2002.            tronomers do their research today.

52
International Workshop on

First Decadal Review of the Edgeworth-Kuiper
Belt: Toward New Frontiers
O. HAINAUT (ESO/Chile)


   On March 11 to 14, 2003, an interna-
tional conference on the Minor Bodies
in the Outer Solar System was held in
Antofagasta, Chile. The conference,
which was organized by ESO and
Universidad Catolica del Norte (UCN) of
Antofagasta, gathered about 70 partici-
pants from 20 countries. Originally, it
was supposed to take place on the UCN
campus. However, a student strike
forced us to relocate at the last minute
to the Carrera Club Hotel. Thanks to the
efforts of A. Lagarini, the conference
secretary (and ESO/Chile Science sec-
retary) and to the Hotel staff, this did not
cause any disruption. The traditional
group photo (opposite) was shot in front
of the Geological Museum of UCN. This
short summary highlights some of the
results presented at this conference;
the proceedings, which are currently           and exciting their eccentricities and in-     Koebert discussed the possibility of a
being edited, will be published as a spe-      clination.                                    perturbation in the EKB as the origin of
cial issue of “Earth, Moon and Planets.”          • A third population is constituted by     the “Late Heavy Bombardment” that the
   Just over 10 years ago, the first           objects that have been ejected by inter-      inner planets suffered 3.8 Gyr ago.
Trans-Neptunian Object (TNO), 1992             actions with Neptune. They are now on         Jancart presented a generic model that
QB1, was discovered by Jewitt and Luu          very eccentric and inclined orbits, con-      considers dissipative force combined
(IAUC 5611). This was the first of about       stituting the “Scattered Disc.”               with the effects of the orbital reso-
700 TNOs known today. They are be-                One of the puzzling problems was           nances.
lieved to be remnants of the proto-plan-       that the “Classical Objects” appear to           After a session full of numerical sim-
etary nebula, the largest objects of the       be distributed in a very dynamically cold     ulations of dynamical processes, the
Edgeworth-Kuiper Belt (EKB), extend-           population (low inclination), mixed with      observers presented the results of on-
ing beyond ~ 30 AU from the Sun, which         a secondary population of higher incli-       going surveys. While over the past
is also the reservoir of Short Period          nation. Gomez and Morbidelli demon-           years, many “generic” surveys discov-
Comets.                                        strated how this can be explained by in-      ered the bulk of the currently known ob-
   Thanks to more and more detailed            teractions of objects of the inner edge of    jects, we see now a specialization of
numerical simulations, which are sup-          the Edgeworth Kuiper belt with                these surveys. Buie et al presented the
ported by a continuously growing num-          Neptune, which would slightly “kick out”      “Deep Ecliptic Survey,” which aims at
ber of objects with well determined or-        these objects. Malhotra and Kuchner           discovering many TNOs of intermediate
bits, the broad lines of the dynamical         further studied, from the theoretical         brightness, with special care in securing
history of these objects now begins to         point of view, the evolution of dust in the   the orbits by carefully planned (and time
be fairly clear. Morbidelli presented a re-    EKB, and compared it with other ob-           consuming) follow up. This follow up is
view of the latest results. The TNOs are       served dust discs, suggesting some            critical, as about half of the known ob-
distributed as follow:                         similarities.                                 jects do not have orbits reliable enough
   • A large fractions are located in the         Many other results were presented;         to ensure their recovery. Moody, and
main belt (the “Classical Objects”),           for instance, Chiang performed exten-         Trujillo and Brown performed extremely
which includes objects with fairly circu-      sive numerical simulations of the reso-       wide, shallow surveys aimed at discov-
lar orbits of low inclination.                 nant objects, showing how they tend to        ering all the brightest TNOs. Unfor-
   • Others have been trapped in stable        cluster at preferred positions leading        tunately, they did not detect any new
motion resonances with Neptune, con-           and trailing Neptune. Wyatt showed            Pluto, although there is still a possibility
stituting the Resonant Population, also        how similar effects could possibly be         to have a couple of objects of that size
known as Plutinos (named after Pluto,          observed in extra-solar Edgeworth-            out there. The survey by Moody et al
the largest member). One of the very           Kuiper belts (also known as circumstel-       has the very sad peculiarity of having
promising theories explaining the num-         lar discs). For instance, the disc around     been terminated by the destruction of its
ber of objects in these resonances in-         Vega displays some striking similarity        telescope, at Mount Stromlo. Fortu-
volves the outward migration of                with his simulations; if confirmed, this      nately, the data are not lost. Kinoshita,
Neptune, a migration caused by the             would imply the presence of (proto-)          Holman and Hainaut have performed
ejection of proto-planetesimals by this        planet around that star. Fernandez, who       some deep to extremely deep surveys
planet, during the early days of the           is one of the founding fathers of the         (with Subaru, VLT and HST) in order to
Solar System. In that process, the sta-        EKB as a reservoir of comets, made            study the faint end of TNO luminosity
ble resonances swept the inner Kuiper          some promising connections between            function. Kinoshita, with his results
belt, trapping the objects encountered,        the Scattered Disc and the Oort cloud.        down to mag ~ 27.7 reported a bent in

                                                                                                                                     53
that luminosity function at mag ~ 24.          Sheppard, Jewitt and Ortiz have ob-            Brucato presented the latest results of
The two other surveys (which should be         tained light curves of several objects,        such work. Cooper and Moroz present-
even deeper, possibly beyond mag 30            which reveal their rotational periods and      ed their studies of irradiation of KBO
by combining 3 nights of data on 2 VLTs        constrain their elongations. While most        surfaces; Cooper detailed the effects of
in parallel) will soon check and refine        objects do not display significant mag-        the various high-energy particles that
this result. Indeed, such a bend is ex-        nitude variations (which is interpreted        are expected to affect objects in the out-
pected, as the power-law luminosity            as almost spherical objects), about a          ermost parts of the Solar System. This
function cannot extend down to dust            quarter of them have light curves with         “space weathering” is considered one of
size. Otherwise, the resulting dust cloud      full amplitude greater than 0.15 mag.          the most important processes explain-
would have been detected by IRAS.              Also, the measurements of 1995 SM55            ing the diversity of colours observed in
The size at which it happens will give di-     (by Sheppard and Jewitt) displayed a           TNOs. Levasseur-Regourd has per-
rect constraints on the importance of          strong dispersion – a controversial re-        formed other laboratory experiments to
disruptive/aggregating collisions and          sult, to which a controversial interpreta-     study the formation of regoliths in micro-
accretion in the early solar system.           tion is attached: this could be the evi-       gravity.
Also, we hope that these deep surveys          dence of cometary activity. Cometary              Pluto, the largest TNO, caused some
will reveal what lies beyond 45 AU,            activity, caused at these distances by         stellar occultations in 2002; these were
where absolutely no object has been            the sublimation of super-volatile ices         the first ones observed since 1985
discovered so far, while the protoplane-       such as CO, should in theory be possi-         when its atmosphere was discovered.
tary nebula is expected to have extend-        ble, but has never been observed. It           Roques (representing the European
ed out to several hundred AU, making           would be an interesting process for re-        team, that was known as the “Pluto
this lack of distant objects one of the        surfacing the objects, possibly explain-       Flying Circus” because of its impressive
most puzzling questions of the field.          ing (part of) their colour diversity. In the   deployment in South America) and Elliot
   The observers continued with physi-         same line, Meech obtained some ex-             presented the interpretations of these
cal studies of TNOs. It is worth remind-       tremely deep images of TNO 24952               occultations, which demonstrate that
ing the reader that TNOs are faint (typi-      with Subaru, in order to search for direct     the atmosphere of Pluto has significant-
cally in the 20–25 mag range) making           evidence of a coma surrounding the ob-         ly changed since 1985. A space mission
their physical studies quite challenging,      ject; her results are negative. The first      to Pluto, which has already been can-
especially for spectroscopy, where the         phase functions of TNOs were present-          celled several times for budgetary rea-
expected absorption features are very          ed by Sheppard and Jewitt, and                 sons, is now finally secured (under des-
shallow. In order to get a grasp of the        Roussellot; they observed a phase de-          ignation of New Horizon Mission), to be
whole population, large photometric            pendency of the brightness much                launched in 2006, for a Pluto/Charon
surveys have been performed, collect-          steeper than expected for icy bodies.          fast fly-by around 2015. As it would be
ing colours of almost 100 objects in to-       Bagnulo obtained the first polarimetric        frustrating to go that far for only one
tal. They reveal a broad distribution          measurements of a TNO–another chal-            (pair of) object, astronomers are now
ranging from neutral (solar) to very red       lenge for the VLT. The phase function          looking for suitable TNOs located on the
colours, the large majority of objects         (which describes the variation of bright-      track of the space probe. Unfortunately,
having a fairly linear reflectivity spec-      ness of the object with the solar phase        these hypothetical candidates are now
trum. Dorressoundiram and Boehnhardt           angle) and the polarimetric characteris-       located in front of the Milky Way, ap-
presented such a survey, performed in          tics of an object can be interpreted in        pearing close to the galactic centre. The
the framework of a VLT large program           terms of surface properties. Barucci, De       field crowding makes the discovery of
(which was concluded during the con-           Bergh and Dotto analysed spectra of            TNOs in these regions very challenging.
ference).      Dorressoundiram          and    TNOs, some of them revealing variable          In the mean time, theoretical studies of
Thebault analysed them by comparing            surface features on some objects.              that object continue: McKinnon present-
them with a model of collisions affecting         Recently, binary TNOs have been dis-        ed models of the interior of Pluto and
the TNOs. Indeed, collisions, by resur-        covered. While binary asteroids tend to        other large TNOs. The very small TNOs
facing the objects, are expected to have       be formed by a main body and a small           were also considered by Keller, who
an effect on their colours. Fulchignoni        satellite, binary TNOs appear as pairs of      summarized the physical properties of
split the objects in families using multi-     fairly similar objects. Noll summarized        cometary nuclei.
variate analysis of their colours, as          the general properties of these objects,          Future survey projects – including
done 30 years ago with the main belt           while Kern, Osip and Takato presented          new methods – were discussed: Alcock,
asteroids, resulting in taxonomic fami-        physical studies of some pairs.                Cooray and Roques plan to discover
lies that were later related to the physi-        The surface of TNOs is expected to          objects by stellar occultations. While
cal nature of the objects. Stephens            be composed by a mixture of dust and           such an event is not very probably, ob-
(who presented a large HST-based               ices. In order to understand the obser-        serving many stars – or observing for a
colour survey) and Peixinho performed          vations, various groups are performing         long time – should lead to many discov-
various statistical tests in order to reveal   laboratory experiments involving the ir-       eries, leading to some information on
possible correlations between the              radiation of ices by high energy parti-        the size and distance of the object. This
colours of the objects and their other         cles, in order to simulate the effect of       is a very promising way to discover the
parameters (orbital elements, size, etc).      cosmic rays on the TNOs. Moore and             smallest bodies of the EKB, and the




Panoramic view of the Monturaqui meteoritic crater. Photo by John Davies.

54
only way to observe comets in the Oort       ers went into the deep Atacama Desert,       lines were traced, the general picture
Cloud. Sekiguchi and Stansberry dis-         lead by L. Barrera from UCN, in order to     was in place. The feeling left by this new
cussed the observations that will be         inspect the Monturaqui meteoritic cra-       conference is that we have now enough
possible with ASTE (the Japanese             ter. This 300-m diameter crater is locat-    information to reveal the weaknesses of
counterpart to APEX) and SIRTF               ed South of the large Salar de Atacama,      this general picture, and that even some
(resp.). Jewitt presented a very ambi-       a 6 hours drive from Antofagasta.            fundamental questions are still unan-
tious project, Pan-STARRS, that will be         Amazingly, none of the participants       swered, such as the reason (or the re-
installed on Mauna Kea and scan the          was lost on the way, which goes against      ality) of a sharp edge terminating the
whole sky on a weekly basis. This pro-       the legend that astronomers cannot be        EKB at 45 AU, or the nature of the
gramme, originally targeted at Near          disciplined when needed.                     processes leading to the observed
Earth Objects, will discover and follow         In 1998, a conference on the same         colour distribution.
up all TNOs down to mag 24.                  topic was held at ESO/Garching. At that         Finally, during the final discussion
   Having 70 astronomers in Anto-            meeting, we were confident that we           session, it was unanimously decided
fagasta, a trip to the VLT was a must.       were on the way to understanding the         that the branch of science devoted to
Bus-loads invaded Paranal on the             TNO formation, evolution, composition,       the study of the TNOs, also designated
Saturday following the conference.           etc, with the enthusiasm of a field that     as Edgeworth-Kuiper belt Object, will be
Finally, on Sunday, 25 brave adventur-       was only a few years old. The broad          known as EKOlogy.




Fellows at ESO
Stefano Ettori                               terms of hard/software assistance and
                                             of motivations, it promotes the interac-
                                                                                          Opportunity stealing valuable telescope
                                                                                          time). My biggest claim to fame during
                         In October 2001,    tion with other researchers with several     my PhD is my contribution to the dis-
                      I started my fellow-   lunch/tea talks, informal discussions        cussion about whether Supernovae and
                      ship in ESO, after 6   and crowded offices (sic!) and is big        Gamma Ray Bursts are connected.
                      years spent at IoA     enough to find anytime the right person         I am currently investigating the fields
                      in Cambridge (Eng-     to discuss with. For my family and my-       around apparently "hostless" super-
                      land) doing my         self, it was a debated question whether      novae (i.e. supernovae which did not
                      PhD and first Post-    to accept this fellowship, but now, and      appear to have a host galaxy) to look for
                      Doc in the X-ray       also considering the difficulties in         faint hosts and, if they exist, investigate
Group headed by Andrew Fabian. My            changing social life in a country with       their properties. So far, all the super-
area of research is clusters and super-      such a strange language (still originat-     novae do appear to have hosts, and in
clusters of galaxies, with particular in-    ing from Ur-germanic but nothing to do       one case, we can still see the superno-
terest on the cosmological implications      with English...), we think we made the       va itself three years after the event! For
of their observed properties. To study       right choice.                                a supernova to be visible after such a
these objects that are the largest virial-                                                long time is highly unusual, and makes
                                                                                          this particular supernova a very inter-
ized structures in the Universe, I look in   Lisa Germany                                 esting object to study – stay tuned for
the optical (with VLT) and X-ray
(through XMM and Chandra) wave-                                                           more on that one!
                                                                    Having arrived at        My other main interest is public out-
bands. These observations allow me to                            ESO       Chile     in
determine densities and temperatures                                                      reach and taking science to the people.
                                                                 September 2000, I        Before starting my PhD I completed a
of the hot plasma collapsed in the dark                          truly feel like one of
matter halo and to recover the cluster                                                    Graduate Diploma in Scientific Com-
                                                                 the veterans of La       munication and have always wanted to
baryonic and gravitational masses. With                          Silla now. There
my collaborators here at ESO, I do this                                                   pursue this further. To my great joy,
                                                                 has been an almost       ESO is developing an exhibition to go
at different redshifts from moderate z =                         complete turnover
0.3, where the X-ray masses can be di-                                                    into the science centre here in
                                                                 of support as-           Santiago, and I am very happy to be
rectly compared to those obtained from                           tronomers since I
weak lensing analyses, up to 1.2 where                                                    part of the team of people working on
                                             arrived, and I have met many of the vis-     that.
few clusters are known through X-ray         iting astronomers on several previous
detection. Of these systems, I have re-      occasions! But this is part of the great
cently used their baryonic mass fraction     thing about working at La Silla - you get    Linda Schmidtobreick
as cosmological tool to put stringent        to talk to astronomers from all over the
constraints on the energy constituents       world, learn about different areas of as-                             When I per-
of the cosmos.                               tronomy and instrumentation, build col-                            formed my first ob-
   My duties at ESO are to support the       laborations, and make new friends.                                 servations in La
release to the community of the ground           I came here straight from my PhD,                              Silla in February
based data of the Chandra Deep Field         which I completed at Mount Stromlo                                 1997, I immediate-
South as part of the Great                   Observatory in Canberra, Australia. I                              ly fell in love with
Observatories Origin Deep Survey             was the 3rd person from Stromlo work-                              the place and de-
(GOODS) project, to represent the            ing here at ESO Chile in 2000/2001,                                cided I wanted to
Fellows and Students in the Computer         and all three of us actually lived in the                          work here some-
Co-ordination Group in Garching and to       same house while we were students!                                 day. In September
maintain X-ray software for the few of       I'm one of these Supernova people            2001 after finishing my PhD, working for
us that are interested in it.                who, along with the Gamma Ray Burst          a year at MPIA Heidelberg, and spend-
   I am really enjoying my time here:        people, are the bane of visiting as-         ing two years as a Postdoc in Padova, I
ESO is a perfect place to work both in       tronomers (all those Targets of              indeed started as an ESO Fellow – with

                                                                                                                                 55
duty station La Silla, of course. Although       come a teacher (Maths, Physics, and                 For my thesis I worked on an HST
the place has sadly changed due to the           Philosophy) the educational work is              survey of Galactic Globular Clusters
closing of the smaller telescopes, I still       something I miss at ESO. However, I try          cores, looking for rare populations such
like the work here very much. The team           to propagate science in public talks and         as blue stragglers and extreme horizon-
spirit is exceptional, the exchange with         articles, I am working in the Museo              tal branch stars, meanwhile testing stel-
the visiting astronomers is very reward-         Interactivo Mirador (Santiago) project           lar evolution models. I also worked on
ing, and I like the practical and technical      (public astronomy exhibition and work-           the determination of the Initial Mass
work of telescope and instrument main-           shops) and will hopefully manage to              Function, and in the problem of ab-
tenance as counterbalance to pure                give some lectures at Chilean Univer-            solute and relative GC ages obviously
thinking and science.                            sities in the near future.                       connected with the measure of dis-
   For the scientific work I find plenty of         During my free time, I try to express         tances. More recently I moved towards
time when off-duty. I have always been           myself in music and painting, I enjoy the        the study of the Galactic bulge, where I
widely interested and hence touched              great life in Santiago, especially in            determined the stellar Initial Mass
several astronomic topics like interplan-        Ñuñoa or Providencia, the part where I           Function down to 0.15 solar masses: a
etary dust, comets, various types of in-         live, and you will always find me with a         power-law with an exponent significant-
dividual stars, structure of the Milky           book close by.                                   ly flatter than Salpeter. With extensive
Way, star formation, and some external                                                            near-IR and optical photometry I re-
galaxies.
   More recently, I have focused on the
                                                 Manuela Zoccali                                  cently set new constraints on both the
                                                                                                  age and metallicity distribution of the
study of the Galactic disc via stellar                                                            bulge.
population analysis, and on Cata-                                     I have been a                  Working at ESO also gave me the
clysmic Variables, where I am mainly in-                            Fellow at ESO                 privilege to work for a new instrument:
terested in the accretion process and                               Garching      since           the VLT fibre spectrograph FLAMES.
the outburst mechanisms of the various                              September 2000.               Joining the FLAMES team and sharing
subclasses. Together with collaborators                             My three years at             the excitement for its success has been
in Chile and all around Europe, we re-                              ESO are about to              fun. It also motivated me to move into
cently recovered the old nova V840                                  end, and in Sep-              high resolution spectroscopy, which, I
Oph, which shows an enormously high                                 tember I will start           believe, is going to represent the key
Carbon content, we followed the dust                                my second post-               tool for our understanding of resolved
production during novae outbursts in                                doc, the Andes                stellar populations.
the sub-mm, and while studying the ac-                              Fellowship, at Uni-              In my little spare time I like to play gui-
cretion disc of RR Pic, discovered evi-          versidad Catolica in Santiago (Chile)            tar, and dream about living by the sea:
dence for a so far unique asymmetric             and Princeton University (USA). Before           swimming, scuba-diving, sailing and
wind.                                            coming to ESO I was in Padova, where             windsurfing, all the hobbies that I’ve been
   Since I have originally studied to be-        I obtained my PhD.                               neglecting too much in the last years.


High Honour to Ray Wilson
RICHARD WEST, ESO
  During a ceremony at the ESO Head-                and former Director General of ESO.
quarters in Garching in the afternoon of            Many of Ray Wilson's friends and col-
28 February 2003, the Order of the                  leagues from the optical and astronom-
French Legion of Honour was bestowed                ical communities in France and at ESO
upon Dr. Raymond N. Wilson, ESO staff               also witnessed the ceremony.
member from 1972-1993.                                 In his presentation, Professor
  The decoration was made by Prof-                  Fehrenbach emphasised the enormous
essor Charles Fehrenbach, member of                 impact of the Active Optics concept on
the French Académie des Sciences and                current astronomy and astrophysics – a
Honorary Director of the Observatoire               fundamental invention made by Ray
de Haute-Provence.                                  Wilson and his team at ESO in the
  On behalf of the French government,               1980's and first implemented with great
the Acting French Consul in Munich,                 success in the 3.5-m ESO New
Mrs Annie Mari, presented Dr. Wilson                Technology Telescope. This concept
with the official scroll. Other speeches            paved the way towards larger telescope
were given by Dr. Catherine Cesarsky                mirrors, effectively overcoming century-
and Professor Lodewijk Woltjer, present             old size and weight limitations. Most of
                                                                      the world's giant tele-
                                                                      scopes         including
                                                                      ESO's own unique            Dr. Wilson (left) receives his honour from
                                                                      Very Large Telescope        Prof. Fehrenbach.
                                                                      are based on this revo-
                                                                      lutionary concept.          pecially in the ESO Optics Group. It was
                                                                         Expressing words of      a great reward for him to witness the un-
                                                                      thanks, Ray Wilson ex-      equalled success of the VLT and to
                                                                      plained how this inno-      sense the daring visions for new and
                                                                      vation was the most         powerful facilities now taking shape
                                                                      visible result of a long,   within ESO and elsewhere in the world.
                                                                      productive and inspir-      An article by Ray Wilson on these de-
                                                                      ing collaboration with      velopments will appear in the Sept-
From left to right: Prof. L. Woltjer, Dr. C. Cesarsky, Dr. R. Wilson, many colleagues, es-        ember issue of The Messenger.
Mrs. A. Mari and Prof. Fehrenbach.


56
The May 7 Mercury Transit
H. BOFFIN and R. WEST, ESO
   On May 7, 2003, the planet Mercury           event itself and also a lot of useful             about 10,000 hits per minute! Many vis-
passed in front of the Sun. This transit,       background information, including spe-            itors therefore needed a little patience to
that occurs approximately once every 7          cial sheets for students and teachers in          see the images. On May 7, the ESO
years, was visible from Europe, Africa          no less than 12 languages. In addition,           website experienced a total of about
and Asia and lasted more than five              a live webcast was held with live images          3.5 million hits and about 50 Gigabytes
hours. European observers were partic-          and a running commentary. Images ob-              of data, mostly images, were delivered.
ularly at their advantage to follow the         tained at observatories in Belgium, the           The great majority of these were from
event as the Sun was relatively high in         Czech Republic, Denmark, Hungary,                 the "Mercury Transit" pages.
the sky during the entire transit. And,         Italy and Spain were shown.                          The May 7 transit of Mercury was a
luckily, the weather did cooperate over            Astronomers at ESO weren’t of course           fine "prelude" to the much more rare
most of Europe.                                 going to miss this opportunity and sever-         event next year when, on June 8, 2004,
   On this occasion, ESO, in collabora-         al telescopes were set-up. In particular, a       the planet Venus will pass in front of the
tion with the European Association for          Meade LX200 equipped with a solar filter,         Sun. On this occasion, ESO plans to
Astronomy Education (EAAE), the                 a Barlow lens and a Nikon D-100 camera            launch, with its educational partners, a
Institut de Mécanique Céleste et de             was used as a “webcam” to provide live            major public programme that will allow
Calcul des Éphémérides (IMCCE) and              images on the web.                                all interested persons to participate ac-
the Observatoire de Paris in France, set           The event was very successful as               tively.
up a comprehensive web site which pro-          shown by the load on the ESO website                 More information can be found on
vided detailed information about the            which reached an all-time record of               http://www.eso.org/outreach/eduoff/vt-2004/.



                                       ANNOUNCEMENTS
                 ESO Fellowship Programme 2003/2004
    The European Southern Observatory awards several postdoctoral fellowships to provide young scientists opportunities and facilities to
 enhance their research programmes. Its goal is to bring them into close contact with the instruments, activities, and people at one of the
 world's foremost observatories. For more information about ESO's astronomical research activities please consult
 http://www.eso.org/science/
    Fellows have ample opportunities for scientic collaborations. A list of the ESO staff and fellows, and their research interest can be found
 at http://www.eso.org/science/sci-pers.html and http://www.sc.eso.org/santiago/science/person.html. The ESO Headquarters in Munich,
 Germany host the Space Telescope European Coordinating Facility and are situated in the immediate neighbourhood of the Max-Planck-
 Institutes for Astrophysics and for Extraterrestrial Physics and are only a few kilometers away from the Observatory of the Ludwig-
 Maximilian University. In Chile, fellows have the opportunity to collaborate with the rapidly expanding Chilean astronomical community in
 a growing partnership between ESO and the host country's academic community.
    In Garching, fellows spend beside their personal research up to 25% of their time on support or development activities of their choice
 in the area of e.g. instrumentation, user support, archive, VLTI, ALMA, public relations or science operations at the Paranal Observatory.
 Fellowships in Garching start with an initial contract of one year followed by a two-year extension.
    In Chile, the fellowships are granted for one year initially with an extension of three additional years. During the first three years, the
 fellows are assigned to either the Paranal or La Silla operations groups. They support the astronomers in charge of operational tasks at
 a level of 50% of their time (split into 80 nights per year on the mountain and 35 days per year at the Santiago Office). During the fourth
 year there is no functional work and several options are provided. The fellow may be hosted by a Chilean institution and will thus be eli-
 gible to apply for Chilean observing time on all telescopes in Chile. The other options are to spend the fourth year either at ESO's
 Astronomy Center in Santiago, Chile, or the ESO Headquarters in Garching, or any institute of astronomy/astrophysics in an ESO mem-
 ber state.
    We offer an attractive remuneration package including a competitive salary (tax-free), comprehensive social benefits, and provide fi-
 nancial support in relocating families. Furthermore, an expatriation allowance as well as some other allowances may be added. The Outline
 of the Terms of Service for Fellows at http://www.eso.org/gen-fac/adm/pers/fellows.html provides some more details on employment con-
 ditions/benefits.
    Candidates will be notified of the results of the selection process in December 2003/January 2004. Fellowships begin between April
 and October of the year in which they are awarded. Selected fellows can join ESO only after having completed their doctorate.

                                              The closing date for applications is October 15, 2003.
    Please apply by:
    • filling the form available at http://www.eso.org/gen-fac/adm/pers/forms/fellow03-form.pdf
    • and attaching to your application:
              - a Curriculum Vitae including a publication list (the latter split into refereed and non-refereed articles, please)
              - a summary of the current and thesis work (max. 1 page)
              - an outline of the research plans if you came to ESO (specify which facilities you foresee to use,
                          whose interest might overlap with yours and what is your motivation to come to ESO (max. 2 pages)
              - an outline of your technical/observational experience (max 1 page)
              - three letters of reference from persons familiar with your scientific work.
    All documents should be typed and in English.
    The application material has to be addressed to:                European Southern Observatory
                                                                    Fellowship Programme
                                                                    Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
                                                                    vacancy@eso.org
    Contact person: Angelika Beller, Tel. +49 89 320 06-553, Fax +49 89 320 06-490, e-mail: abeller@eso.org
    All material, including the recommendation letters, must reach ESO by the deadline (October 15); applications arriving af-
 ter the deadline or incomplete applictions will not be considered!


                                                                                                                                             57
             Call for Proposals for a Third Generation
                       Instrument for the NTT
 Introduction                                    cellent quality of the telescope and the su-      ture observing modes with the ESO NTT.
                                                 perb observing conditions at La Silla. It            Deadline: August 31st, 2003
     The scientific mission of the La Silla      should complement the VLT and other fu-
 Observatory is periodically reviewed (typi-     ture facilities (VST, VISTA, ALMA), provide       Intent to submit a proposal to build
 cally every 3 years) by special ad-hoc          unique scientific results in its own merit and    a new instrument for the NTT
 Committees, appointed by the ESO                address the needs of a significant segment
 Director General and composed of mem-           of the community. On the technical side,             ESO solicits proposals to build a new in-
 bers of the User’s Committee (UC), the          ESO would favor an instrument easy to op-         strument for the NTT from Institutes or
 Scientific Technical Committee (STC), and       erate and with a reasonable cost.                 groups of Institutes. The project could be
 ESO staff. The reports of these Committees         This Call is addressed to all past or po-      developed in collaboration with ESO, and in
 have been presented to STC and Council          tential users of the ESO telescopes. Any          particular with the La Silla Observatory. The
 and used in planning the long range strate-     astronomer working in an ESO member               framework would be the one used in other
 gy of ESO. The three successive La Silla        country (including ESO staff) is warmly in-       VLT or La Silla collaborative projects, where
 Committee reports (LS2000, LS2000+, and         vited to provide his/her input. This can be in    the contribution by an external Consortium
 LS2006+) have been widely distributed in        the form of a recommendation on how to            in manpower and/or cash is rewarded with
 the community, and one of them (LS2000+)        proceed or as a formal letter of intent ex-       guaranteed observing time.
 is available on-line through the ESO web        pressing the interest in developing a new            In this case, the PI should forward (1) a
 site (www.eso.org).                             instrument, as spelled out in the next two        conceptual description of the instrument
     One of the key recommendations of the       sections.                                         he/she is proposing and of its scientific
 LS2006+ Committee (chaired by A. Cimatti                                                          drivers and operating model; (2) the main
 of Arcetri Observatory) was to quickly re-      Survey on the observing modes to                  Institute(s) which are expected to be asso-
 place one of the existing instruments at the    be offered at the NTT                             ciated to the project and the preliminary en-
 NTT by a next generation one, in order to                                                         dorsement by the Director of the leading
 keep the telescope facility fully competitive      ESO is interested in your properly justi-      Institute and (3) the contribution expected
 beyond 2006. Present instruments in oper-       fied view on these specific points:               from ESO.
 ation at the NTT are: 1) EMMI, a multi-mode        (a) Which among the existing NTT in-              For technical information on the NTT,
 spectro-imager in the Visible domain, in-       struments will be mostly needed beyond            please contact Emanuela Pompei (epom-
 stalled in 1990; 2) SUSI, the SUperb-           2006 and with what mode(s);                       pei@eso.org) at La Silla Observatory.
 Seeing Imager installed in 1991 and up-            (b) Which observing mode(s) currently             The above expression of intent should be
 graded to SUSI2 in 1998 and 3) SOFI –Son        not offered at the NTT would be most inter-       forwarded by e-mail to gmonnet@eso.org
 OF Isaac– a near-IR spectro-imager, which       esting to complement the VLT capabilities         and to jmelnick@eso.org. As Subject,
 originated as an early spin-off from the de-    and make unique science.                          please enter: Proposal to build an instru-
 velopment of ISAAC for the VLT and was             (c) Whether an NTT focus for visitor in-       ment for the ESO NTT.
 put into operation also in 1998.                struments should be given high priority              The e-mails should be timely followed by
     Five years into VLT operations and after                                                      a formal Letter of Intent addressed to:
 15 years of successful NTT operations, it is        Please add any other consideration rele-                  Head Instrumentation Division
 indeed timely –as proposed by the LS2006+       vant for the choice of future NTT instru-                     Attention: G. Monnet
 Committee and recommended by the STC–           mentation. In particular, you may comment                     Subject: New NTT Instrument
 to reassess the scientific mission of the ex-   on the need for a new general use capabil-                    European Southern Observatory
 isting NTT instrumentation and how it could     ity or instead on some new facility dedicat-                  K. Schwarzschild Str. 2
 be partly or totally replaced with a new in-    ed for a large fraction of NTT time to a spe-                 D- 85748 Garching b. München
 strument and/or with easy access to a visi-     cific and challenging scientific goal (like the      E-mail deadline: August 31st, 2003
 tor focus. Any new instrument would have        extensive exo-planet search with HARPS at
 to physically replace either SOFI/SUSI or       the 3.6 m).                                          The proposals will be technically and
 EMMI. It should offer to the community an           Your contribution should be sent by email     managerially assessed by ESO and pre-
 end to end observing capability at the fron-    to epompei@eso.org and sdodoric@                  sented to the STC in October 2003 for a
 tier of present astrophysical research, tak-    eso.org .                                         recommendation, together with the results
 ing into account the medium size and ex-            As Subject, please enter: Survey on fu-       of the survey in the community.




Kurt Kjär retires from ESO
                                  After a long and dedicated service to ESO, Kurt          perience, especially visible during the all too frequent
                               Kjär is retiring from the post of Technical Editor which    hectic periods to meet imposed deadlines. The
                               he has held during an unprecedented period of al-           European astronomical community has witnessed the
                               most 30 years.                                              steady progress of the ESO Messenger from the first
                                  From the beginning, ESO has profited enormously          thin issue in 1974 to the current, very comprehensive
                               from his solid technical expertise and thoroughness,        ones. This would not have been possible without a
                               great sense for form and content and, not least, im-        close and friendly, highly effective collaboration be-
                               pressive knowledge of languages. He has been                tween Kurt Kjär and the various Messenger editors.
                               deeply involved in and has put his personal stamp of        As one of these, I am happy to testify here to the fan-
                               quality on hundreds of ESO publications at all levels       tastic stimulus and help it has been to work with a per-
                               and scopes, ranging from the Annual Report, the             son like Kurt. We are all deeply thankful to him.
                               ESO Messenger, ESO conference proceedings and                  Kurt Kjär will retire to live with his wife in
                               scientific preprints to technical reports and brochures,    Oberschleissheim, a few kilometres from the ESO
                               etc. Much time and many resources have been saved           Headquarters.
                               thanks to his profound knowledge and enormous ex-                                                    Richard West




58
 The Instrumentation Division at the ESO Headquarters in Garching near Munich, Germany, offers the following job opportunity:


 Head of the Instrumentation Division                                                                               Career Path: VII
    Assignment: The Head of the Instrumentation Division directs all ESO-activities pertaining to optical and infrared astronomical instru-
 mentation and reports directly to the Director General. As a member of the ESO Management, the Head of Divison contributes directly
 to the development of the overall policy, strategic planning and maintains professional contacts at highest level outside the Organisation.
 The Instrumentation Division consists of about 30 astronomers, physicists and engineers, who work in groups or teams developing in-
 frared and optical instruments and detectors. They also receive extensive support from the ESO Technical Division e.g. in the areas of
 optical design, electronics hardware and software. The main tasks of the Division are:
    • to develop, test and install state-of-the-art instruments, for both in-house projects and those involving collaborations with consortia of
 external suppliers or institutes;
    • to support in the maintenance and upgrading of the instruments at the Observatories;
    • to conduct a future advanced instrumentation programme through design studies, preparation of proposals, development and test-
 ing of critical components and subsystems.
    As a Senior Astronomer the Head of the Instrumentation Division is a member of the ESO Science Faculty and is expected and en-
 couraged to conduct active astronomical research.
    Qualifications and Experience: Basic requirements for the position include a PhD in astronomy, astrophysics or physics or related
 fields, a proven record of scientific leadership, experience in international scientific collaborations and at least 10 years' experience in the
 design and use of astronomical instrumentation. Substantial management and leadership experience within a scientific organisation,
 preferably international, is required. Excellent communication skills and a very good knowledge of English are essential.
    Duty station: Garching near Munich, Germany, with regular duty travels to Chile.
    Starting date: as soon as possible
    Remuneration and Contract: We offer an attractive remuneration package including a competitive salary (tax-free), comprehensive so-
 cial benefits and financial help in relocating your family. The initial contract is for a period of three years with the possibility of a fixed-term
 extension. Serious consideration will be given to outstanding candidates willing to be seconded to ESO on extended leaves from their home
 institutions. Either the title or the grade may be subject to change according to qualification and the number of years of experience.
    Application: If you are interested in working in a stimulating international research environment and in areas of frontline science and
 technology, please send us your CV (in English) before 31 July 2003

   All applications should include the names of four individuals willing to give professional references.

    For further information, please contact Mr. Roland Block, Head of Personnel Department, Tel +49 89 320 06 589, e-mail:
 rblock@eso.org. You are also strongly encouraged to consult the ESO Home Page (http://www.eso.org).

   Although preference will be given to nationals of the Member States of ESO: Belgium, Denmark, France, Germany, Italy, The Netherlands, Portugal,
 Sweden, Switzerland and United Kingdom, no nationality is a priori excluded. The post is equally open to suitably qualified male and female applicants.




PERSONNEL MOVEMENTS                                                                 BRYNNEL, Joar (S), Electronic Engineer
                                                                                    CIASTO, Hubert (D), Senior Administrative Assistant
                                                                                    GALLIANO, Emmanuel (F), Student
International Staff                                                                 HATZIMINAOGLOU, Evanthia (GR), Associate
(1 March – 31 May 2003)                                                             HOFFMANN-REMY, Martin (D), Internal Auditor
                                                                                    KJÄR, Kurt (D), Technical Editor
ARRIVALS                                                                            MAINIERI, Vincenzo (I), Student
 EUROPE                                                                             PIRZKAL, Norbert (F), Science Systems Analyst/Programmer
    ACCARDO, Matteo (I), Mechanics Technician
    BOFFIN, Henri (B), Editor
                                                                                 CHILE
    BRAST, Roland (D), Electrical Engineer/Senior Technician                        FAURE, Cécile (F), Student
    LUNDIN, Lars Kristian (DK), Data Analysis Specialist/Software                   WOODS, Paul (GB), Student
       Engineer
    LYNAM, Paul (GB), Associate
    MACKOWIAK, Bernhard (D), Associate
                                                                              Local Staff
    MEUSS, Holger (D), ALMA Archive Software Developer                        (1 February 2003 – 31 May 2003)
    NASS, Petra (D), Operations Support Scientist
    NYLUND, Matti (S), Software Engineer
    OBERTI, Sylvain (F), Assembly Integration and Testing Engineer            ARRIVALS
    PUECH, Florence (F), VLTI System Engineer
                                                                                    ARANDA CONTRERAS, Ivan, Archival Technician
    SCHILLING, Markus (D), ALMA Software Developer
                                                                                    CID FUENTES, Claudia, Telescope Instrument Operator
    SCHUHLER, Nicolas (F), Student
                                                                                    CORTES CARVALLO, Angela, Telescope Instrument Operator
    VOIRON, Samuel (F), Student                                                     DONOSO MARIN, Reinaldo, Maintenance Mechanical
                                                                                      Technician
 CHILE                                                                              GUAJARDO OBANDO, Patricia, Telescope Instrument
    DEL BURGO, Stephan (F), Optical Engineer                                          Operator
    DEPAGNE, Eric (F), Fellow                                                       SANZANA ROJAS, Lilian, Software Engineer
    GONCALVES, Nelson (P), Associate
    JEHIN, Emmanuel (B), Operations Staff Astronomer                          DEPARTURES
    RANTAKYRÖ, Fredrik (S), VLTI Astronomer
                                                                                    AMESTICA VALENZUELA, Rodrigo, Joint Software Group
DEPARTURES                                                                            Leader
 EUROPE                                                                             BAEZA ARAYA, Silvia, Software Engineer Developer
    ALEXOV, Anastasia (USA), Science Data Analyst/Programmer                        BARRIGA CAMPINO, Pablo, Instrumentation Engineer


                                                                                                                                                      59
ESO, the European Southern Observa-           ESO Workshop on Large Programmes and Surveys
tory, was created in 1962 to “... establish
and operate an astronomical observato-        S. WAGNER (OPC) and B. LEIBUNDGUT (ESO)
ry in the southern hemisphere, equipped          On 19 to 21 May, 2003, the scientific im-          had the effect of unifying the community in
with powerful instruments, with the aim of    pact of Large Programmes was assessed at              certain astronomical fields.
furthering and organising collaboration       a workshop in Garching. Several members                  The effectiveness of the restriction of LPs
in astronomy...” It is supported by ten       of the OPC and STC actively participated in           to two years duration was cited as a good in-
countries: Belgium, Denmark, France,          the workshop.                                         centive to produce important results quickly,
Germany, Italy, the Netherlands, Portu-          Every PI of a Large Programme (LP) ap-             one major reason to originally introduce the
gal, Sweden, Switzerland and the United       proved up to ESO Period 69 was invited to             LPs.
Kingdom. ESO operates at two sites in         present the results of their project. All LPs            Overall the LPs are considered a success
the Atacama desert region of Chile. The       but one were presented in half-hour talks. A          and should be continued. They provide
new Very Large Telescope (VLT), the           two-hour discussion session was held to as-           European astronomers with the opportunity
largest in the world, is located on           sess whether the current scheme of LPs is             to achieve important results in a competitive
Paranal, a 2,600 m high mountain ap-          adequate or should be adjusted.                       and timely fashion.
proximately 130 km south of Antofa-              The general impression was that most                  The OPC discussed the outcome of the
gasta, in the driest part of the Atacama      LPs have produced excellent results and               workshop at its meeting on June 2 and de-
desert where the conditions are excellent     unique science, which would have been un-             cided to continue with Large Programmes
for astronomical observations. The VLT        achievable through regular programmes.                with P73. ESO will accept Large Program-
consists of four 8.2-metre diameter tele-     They allowed European astronomers to di-              mes for this period again.
scopes. These telescopes can be used          rectly compete with the best American                    An article on the workshop providing more
separately, or in combination as a giant      groups, some of whom profit from significant          details will appear in the next issue of The
interferometer (VLTI). At La Silla, 600 km    access to large telescopes. The LPs have              Messenger.
north of Santiago de Chile at 2,400 m
altitude, ESO operates several optical
telescopes with diameters up to 3.6 m
and a submillimetre radio telescope           Contents
(SEST). Over 1300 proposals are made
each year for the use of the ESO tele-
scopes. The ESO headquarters are lo-          TELESCOPES AND INSTRUMENTATION
cated in Garching, near Munich, Ger-
many. This is the scientific, technical and   C. Cesarsky: Progress with the Atacama Large Millimeter Array . . . . . 2
administrative centre of ESO where tech-      F. Primas: The Science Verification of FLAMES . . . . . . . . . . . . . . . . . 3
nical development programmes are car-         R. Arsenault et al.: MACAO-VLTI First Light:
ried out to provide the Paranal and La            Adaptive Optics at the Service of Interferometry . . . . . . . . . . . . . . 7
Silla observatories with the most ad-
vanced instruments. There are also ex-        Ch. Leinert et al.: MIDI Combines Light from the VLTI:
tensive astronomical data facilities. ESO         the Start of 10 µm Interferometry at ESO . . . . . . . . . . . . . . . . . . .13
employs about 320 international staff         L. Germany: News from La Silla . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18
members, Fellows and Associates in
Europe and Chile, and about 160 local
staff members in Chile.                       REPORTS FROM OBSERVERS
The ESO MESSENGER is published                G. Rudnick et al.: Studying High Redshift Galaxy Clusters with the
four times a year: normally in March,             ESO Distant Cluster Survey . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19
June, September and December. ESO             R. Napiwotzki et al.: SPY — The ESO Supernovae Type Ia
also publishes Conference Proceedings,
Preprints, Technical Notes and other ma-          Progenitor Survey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25
terial connected to its activities. Press     R.G. Gratton et al.: Abundances in Globular Cluster Dwarfs . . . . . . . .31
Releases inform the media about partic-       M. Arnaboldi et al.: Intracluster Planetary Nebulae in the Virgo
ular events. For further information, con-        Cluster: Tracers of Diffuse Light . . . . . . . . . . . . . . . . . . . . . . . . . .37
tact the ESO Education and Public
Relations Department at the following
                                              F. Barrientos et al.: The Red-Sequence Cluster Survey . . . . . . . . . . .40
address:                                      M. Rejkuba et al.: Long Period Variables in the Giant Elliptical
                                                  Galaxy NGC 5128: the Mira P-L Relation at 4 Mpc . . . . . . . . . . . .43
EUROPEAN                                      H. Dejonghe et al.: The Dynamics of Dwarf Elliptical Galaxies . . . . . .47
SOUTHERN OBSERVATORY
Karl-Schwarzschild-Str. 2
D-85748 Garching bei München                  OTHER ASTRONOMICAL NEWS
Germany
Tel. (089) 320 06-0                           U. Grothkopf: From Books to Bytes:
Telefax (089) 3202362                            Changes in the ESO Libraries over the Past Decade . . . . . . . . . . .51
ips@eso.org (internet)
URL: http://www.eso.org
                                              O. Hainaut: International Workshop on “First Decadal Review of the
http://www.eso.org/gen-fac/pubs/                 Edgeworth-Kuiper Belt: Toward New Frontiers” . . . . . . . . . . . . . . .53
messenger/                                    Fellows at ESO: Stefano Ettori, Lisa Germany, Linda Schmidtobreick
                                                 and Manuela Zoccali . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .55
                                              R. West: High Honour to Ray Wilson . . . . . . . . . . . . . . . . . . . . . . . . .56
The ESO Messenger:
Editor: Peter Shaver                          H. Boffin and R. West: The May 7 Mercury Transit . . . . . . . . . . . . . . .57
Technical editor: Henri Boffin
                                              ANNOUNCEMENTS
Printed by
Universitätsdruckerei                         ESO Fellowship Programme 2003/2004 . . . . . . . . . . . . . . . . . . . . . . .57
WOLF & SOHN
Heidemannstr. 166                             Call for Proposals for a Third Generation Instrument for the NTT . . . .58
D-80939 München                               R. West: Kurt Kjär retires from ESO . . . . . . . . . . . . . . . . . . . . . . . . . .58
Germany                                       ESO Vacancy: Head of the Instrumentation Division . . . . . . . . . . . . . .59
                                              Personnel Movements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .59
ISSN 0722-6691
                                              ESO Workshop on Large Programmes and Surveys . . . . . . . . . . . . .60

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