VIEWS: 16 PAGES: 60 POSTED ON: 12/31/2012
No. 112 – June 2003 Computer simulation of the Atacama Large Millimeter Array (ALMA). Image created by Herbert Zodet. 1 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, email@example.com 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 firstname.lastname@example.org Contact person: Angelika Beller, Tel. +49 89 320 06-553, Fax +49 89 320 06-490, e-mail: email@example.com 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); firstname.lastname@example.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 email@example.com OF Isaac– a near-IR spectro-imager, which esting to complement the VLT capabilities and to firstname.lastname@example.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 email@example.com 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: firstname.lastname@example.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 email@example.com (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 60
"MACAO-VLTI First Light - ESO"