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					                     A STEP
Antarctica Search for Transiting
      Extrasolar Planets
                                   F.Fressin, T.Guillot
 Y.Rabbia, A.Blazit, JP. Rivet, J.Gay, D.Albanese, V.Morello, N.Crouzer (OCA - Nice),

                   F.X Schmider, K.Agabi, J-B. Daban, E.Fossat,
                L.Abe, C.Combier,F.Janneaux,Y. Fantei (LUAN – Nice)

     C.Moutou, F.Bouchy, M.Deleuil, M.Ferrari, A.Llebaria, M.Boer, H.Le Corroler,
            A.Klotz,A.Le van Suu,J. Eysseric, C Carol (OAMP - Marseille),

                          A.Erikson, H.Rauer (DLR - Berlin),

                                F.Pont (Obs. Genève)
             The future of transit searches

                             Combined to radial-velocimetry, it is
                             the only way to determine the
                             density, hence the global composition
                             of a planet


                             Transit spectroscopy offers
                             additional possibilities not accessible
                             for “normal” planets

We foresee that exoplanetology
will have as its core the study of
transiting exoplanets


examples:
A correlation between the metallicity of stars
and planets (Guillot et al. A&A 2006)

Planetary formation model constraints
(Sato et al 2005)
            The future of transit searches
2 future milestones:
•COROT: 60 000 stars (nominal mission), mv=11 to 16, for 150 days, launch oct. 2006
•KEPLER: 100 000 stars, mv=11 to 14 for 4 years, + 70 000 for 1 year, launch end 2008

Limited by data transmission to Earth
A problem for the detection of small planets: background eclipsing binaries



                            Future missions should:
                            •Detect more planets
                            •Diversify the targets
                            •Detect smaller planets



    from SPACE                                   from DOME C
    •Natural but costly                          •Promising but uncertain
    •Limited in telescope size,                  •Requires precursor mission(s)
    number of instruments...
   Why transit searches at Dome C?

•Continuous night for 3 months
•Excellent weather

Questions:
We don’t know how the following factors will affect transit surveys:
    •Sky brightness & fluctuations
    •Presence of the moon
    •Generally, systematics effect due to the combination of
    astrophysical, atmospheric and instrumental noises

Technical problems
    •Autonomous operations in cold (-50°C to -80°C) conditions
    •Temperature fluctuations
    •Icing
    •Electrical discharges
          A STEP Objectives

1.   Determine the limits of Dome C for precise wide field
     photometry (Scintillation and photon noise … or other
     noise sources ?)

2.   If the site is competitive with space and transit search
     limits are well understood, establish the bases of a mid-
     term massive detection project (large Schmidt telescope
     or network of small ones)


3.   Search for transiting exo-planets and characterization of
     these planets – Detection of bright stars oscillations.
A STEP: the philosophy behind

•Prepare future photometric projects for
planetary transit detection at Dome C

•Use available equipment, minimize development
work for a fast implementation of the project

•Use experience acquired from the site testing
experiment Concordiastro

•Semi-automated operation

•Directly compare survey efficiency at Dome C
with BEST 2 in Chile for the same target field
                 Ground based transit projects
                                                                          Fie ld
                                                                                 Limiting
Program    Obse rving site      Status      Tele scope Instrume nt        of               Stars/FOV Precision
                                                                                 magnitude
                                                                          Vie w
                                                       Spectral
                                                       Instruments-560,
           Mt. Hamilton,                               Kodak                  x
Vulcan                          observing   5,4 cm                                13 mag   6000     1%
           California                                  KAF16800 4k x
                                                       4k CCD, Canon
                                                       EF300 F/2.8
                                                       Apogee AP 10,
                                                       Thomson
                                under                                         x
Hat-1      Kitt Peak, Arizona                6,4 cm    THX7899M 2k x              13 mag   20000    0,01 mag
                                construction
                                                       2k, Nikon
                                                       180mm f/2.8 MF
                                                       Apogee AP 10
ASAS-3     Ź                    observing   7,1 cm     2k x 2k, Minolta   x       14 mag   8000     Ź
                                                       200/2.8
           Tenerife, Canary                            Pixelvision 2k x
STARE                           observing   10 cm                                 Ź        25000    Ź
           Islands                                     2k CCD, f/2.9
                                                       CCD AP10
           Thueringer
                                                       Apogee,
BEST       Landessternwarte, observing      20 cm                         x       13 mag   30000    < 1%
                                                       Thomson
           Germany
                                                       THX899M
                                                       F/2.8 Nikon,
                                                       Apogee 10 CCD          x
                                                                                                                 10 transiting planets
WASP0      Ź                    Project     10 inch                               14 mag   Ź        1%
                                                       camera
                                                       (2k x 2k)
                                                       Canon 200mm
                                                       f/1.8, 2k x 2k
                                                                                                                 discovered up to date
          La Palma, Canary under
                                                                                                                  – 4 radial velocities +
SuperWASP                               11,1 cm        thinned EEV      x         13 mag   43000    Ź
          Islands          construction
                                                       produced by

                                                                                                                    photometric follow up
                                                       Andor of Belfast
           Siding Spring
                                                                              x
                                                       Ź                                   Ź
                                                                                                                  – 5 OGLE
APT        Observatory,         observing   80 cm                                 13 mag            1%
           Australia

                                                                                                                  – 1 STARE/TrES
                                                       8kMOSAIC CCD
           Las Campanas
                                                       camera (SITe     35' x
OGLE       Observatory,         observing   130 cm                            Ź            Ź        Ź
                                                       2048 x 2049 thin 35'
           Chile
                                                       chip )
           Tenerife, Canary     under                          NIMO
                                                       CCD42-40Ź
STELLA                                       ???                    Ź             Ź        Ź        Ź
           Islands              construction           2k x 2k
                                                       Apogee AP10,
                                                       Thomson 7899M 19,5
           Fenton Hill ,   under
RAPTOR A                                70 cm          CCD 2k x 2k,  x    12 mag           Ź        Ź
           Jemez Mountains construction
                                                       Canon 85mm    19,5
                                                       f/1.2
      Transits photometry – Any problem ?
     A huge difference between the expected number of detections and
     reality :
               Number of detections   Real number of    Simulation considering
     Project   expected per season      detections     « systematic effects »

     STARE              14                  1                   0.9
     OGLE              17.2                1.2                   1.1
     HATnet             11                  0                   0.2
     Vulcan             11                  0                   0.6
     UNSW              13.6                 0                   0.01


         DUTY CYCLE

These numbers really depend of the
duty cycle of each campaign

         Red Noise

These red noises, or «systematic
effects » are all the noises undergoing
temporal correlations and that we can
not subtract easily.
                Systematic effects (F.Pont 2005)

•We only have a partial knowledge of these
effects

•They seem to all result from interaction
between environmental effects with
instrumental characteristics (Pont 2005)

•They are closely linked to the spatial
sampling quality

•For OGLE, the principal source is
differential refraction linked to air mass
changes. (Zucker 2005)


                                             — magnitude dependence with white noise
                                             — magnitude dependence with red noise
            Continuous observations
                                     With a “classical” survey, only
                                     the “stroboscopic” planets are
                                     detectable !
A good phase coverage is
determinant to detect the
large majority of transits
from ground

OGLE: transits discovered
•really short periods P ~ 1 day
(rare !)
•stroboscopic periods

Hot Jupiters: periods around
3 days, depth ~1%
                                  Probability of detection of a transit
                                  for a survey of 60 days

                                  With OGLE

                                  For the same telescope with a
                                  permanent phase coverage
       Observing at dome C – Lessons from first
               two winter campaigns (1)

An exceptional coverage …
 Confirmation by the first winter campaign of the exceptional phase
coverage (cloud coverage, austral auroras)

« First Whole atmosphere night seeing measurements at Dome C, Antarctica »
Agabi, Aristidi, Azouit, Fossat, Martin, Sadibekova, Vernin, Ziad



 Environmental systematic effects considerably reduced:
• air mass
• timescale of environmental parameters evolution

Expectations for future transits search programs
• low scintillation
       Observing at dome C – Lessons from first two
                   winter campaigns (2)

… But a lot of technical difficulties to take
into account
 Frost – different
Behaviour for different
telescopes

Differential dilatations
inside the telescope


Telescope mounts
missfunctionning at
really low temperature
         Observatoire de la Côte d'Azur (Laboratoires Cassiopée et Gemini):

         Tristan Guillot                 Scientific preparation, operation supervision, preparation of
         (PI)                            modelling tools, analysis of the results and scientific interpretation

                                         Scientific and technical preparation, modelling tools, analysis of
         Francois Fressin (IS)
                                         the results and scientific interpretation

                                         Responsible of the camera team; Developpement of test and
         Alain Blazit
                                         acquisition tools.

                                         Follow-up of the telescope conception; Technical preparation,
         Jean Gay
                                         optical properties modelling

 THE     Yves Rabbia                     Telescope environment, follow-up of the telescope conception


A STEP   Jean-Pierre Rivet               Telescope environment, flat fielding system


TEAM
         Dominique Albanese              Camera control softwares & camera testing expertise

         Laboratoire Universitaire d'Astrophysique de Nice:

                                         Scientific and technical preparation (telescope), Dome C logistics,
         François-Xavier Schmider
                                         analysis of the results and scientific interpretation

                                         Technical preparation, Dome C logistics, telescope design and
         Karim Agabi (PM)
                                         telescope control systems

                                         Technical preparation, Dome C logistics, telescope design and
         Jean-Batiste Daban
                                         telescope control systems

                                         Dome C logistics, analysis of the results and scientific
           A STEP Telescope

                       A STEP Characteristics:

                       Camera use:
                       Defocused PSF
CCD DW 436 (Andor)
Size 2048 x 2048
                       PSF sampling: FWHM covering ~4 pixel
Pixel size 13.5 mm     Time exposure: 10s
1.74 arcsec on sky     Readout time: 10s

                       Telescope mount:
                       German Equatorial Astrophysics 1200
                       With controlled heating
                       Pointing precision tolerated ~.5”

                       Contractor:
                       Optique et Vision
                       ERI
A STEP Camera : Andor DW436


         -2048x2048 pixel
         -Backwards illuminated CCD
         -Limited intra-pixel fluctuations
         (Karoff 2001)
         -Excellent quantum efficiency in red
         -USB2 with antarctisable connection
A precise photometric telescope at Dome C

              Telescope tube:
              INVAR structure
              With Carbon fiber coverage




4Mpixel DW436 CCD      Wynne Corrector     Thermal enclosure for
                                           focal instrumentation
             Mode of operation


• One field followed continuously (first year)
• Flatfields from illuminated white screens
• Data storage: ~500 GB /campaign
• Data retrieval at the beginning of Antarctic Summer
• Redundancy:
    -Two computers in an “igloo” next to the telescope
    -Two miror PCs in the Concordia Command Center
    (fiber link)
    -Two backup PCs
•Semi-automatical:
    -Simple control and maintenance every 48 hours
Target stellar field for first campaign
    Data processing
 Re-use of the major part of BEST
(Berlin Exoplanet Search Telescope)
   data pipeline (Erikson, Rauer)
Schedule of A STEP


             •PNP, CSA: 64 k€ (approved)
             •ANR: 208 k€ (pending)
Schedule of A STEP
                              CoRoTlux
  Stellar field generation
 with astrophysical noise sources        Blends simulation




   Light curves generation
and transit search algorithms coupling
                            Expected results …
Using CoRoTlux simulator (end to end
stellar field to light curves generator)




                                           Transit Depth
Guillot, Fressin, Pont, Marmier, …




Considering only planets Giant
Planets (Hot Saturn and Jupiter)

Simulation done with CoRoTlux




                                           Transit Depth
considering 4 stellar fields (1 first
year, 3 second year)

Average of 12 Giant Planets for 10
Monte-Carlo draws
                                                            11   12   13      14     15   16   17
                                                                      Stellar Magnitude

                                                           Exemples of results of two
                                                             CoRoTlux simulations
False Transit
Discrimination
         Many events mimic transits … !
                    Number of events for 1 CoRoT CCD
                        CoRoTlux (Guillot et al.)

Grazing Eclipsing
    Binaries

                                 background
                                 eclipsing binaries



  M Dwarfs
                                            target
                                            planets

                          background
                          planets                     target
 Triple Systems                                       binaries
                    Blends discrimination
Within lightcurve:                 Ground based follow-up:

+Secondary transits                +Radial velocities (provides
+Detection level                   confirmation by a different
+Exoplanet “diagnostic” or         method AND planet
“minimal radius” Tingley &         characterization) – HARPS
Sackett
+Ellipsoidal variability of        +Precise photometry with
close binaries                     high resolution telescopes and
(Sirko & Paczynski 2003)           Adaptive optics for critical
+ Photocenter of the               cases
fluctuation


-> 70 to 90 % of transit
candidates could be                ->99+ % false events
discriminated within lighturves    discrimination goal
(Estimation from CoRoTlux          -> confirmation of most transits
results – Fressin)                 with radial velocities … ?
                           Conclusions
       • A STEP
            – Is supported by 6 laboratories, French Dome C commission, Exoplanet
              group, Planetology National Program
            – Would allow to detect in one season as many transits as all other
              ground based transit programs in several years.
            – Will do the photometric test of Dome C for future transit search
              programs …

• CoRoT
  - Will discover and characterize most of the short period giant
  planets in its fields, thus largely increase our knowledge of exoplanets
  - Will provide statistical information on the presence of short
  periods smaller planets
  - Could provide the first characterization of super-earth planets


   Transit research is determinant for exoplanet
     characterization
   – Planetary formation and solar system models
   – A cornerstone for exobiology programs
              Global ongoing study:
Simulation of the optimal transit search program

 COROTLUX
 ->Stellar Field
 generator – Guillot et al
 (astrophysical noise
 sources)

                Point Spread Function and image
                on CCD – (Fressin, Gay)
                (instrumental and atmospheric
                noises – masks/PSF fitting)

 Light curves generator
 -> Systematic and
 environmental effects



                Search of transits in
                lightcurves
                -> Treatment, transit
                search, discrimination
                (-> Number of detections)
         Why searching for transits?
                                     Only possible way known to measure
                                         an exoplanet radius

                                     Combined with radial velocity
   Radius                                measurements:
measurement
               Mass Measurement           Mass, density,
               (radial velocities)           composition
(photometry)
                                     Capacity to detect small objets
                                          Jupiter: 1%; Earth: 0.01%


                                     Ground based projects were almost
                                         unable to discover objects like
                                         Hot Jupiter up today –

                                     But there will be great returns as
                                          their detection threshold
                                          increases

				
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