A STEP

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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)
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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
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. AA
2006) Planetary formation model constraints
(Sato et al 2005)
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The future of transit searches

• 2 future milestones
• COROT 60 000 stars (nominal mission), mv11 to
  16, for 150 days, launch oct. 2006
• KEPLER 100 000 stars, mv11 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
• Natural but costly
• Limited in telescope size, number of
  instruments...

• from DOME C
• Promising but uncertain
• Requires precursor mission(s)

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Why transit searches at Dome C?

• Continuous night for 3 months
• Excellent weather

• Questions
• We dont 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 (-50C to -80C)
  conditions
• Temperature fluctuations
• Icing
• Electrical discharges

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A STEP Objectives

• Determine the limits of Dome C for precise wide
  field photometry (Scintillation and photon noise
  or other noise sources ?)
• 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)
• Search for transiting exo-planets and
  characterization of these planets Detection of
  bright stars oscillations.

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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

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Ground based transit projects

• 10 transiting planets discovered up to date
• 4 radial velocities photometric follow up
• 5 OGLE
• 1 STARE/TrES

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Transits photometry Any problem ?
A huge difference between the expected number of
detections and reality Project STARE OGLE HATn
et Vulcan UNSW
Number of detections expected per
season 14 17.2 11 11 13.6
Simulation considering  systematic
effects  0.9 1.1 0.2 0.6 0.01
Real number of detections 1 1.2 0 0 0
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.
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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
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Continuous observations

• 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
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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

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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

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Observatoire de la Côte d'Azur (Laboratoires Cassiopée et Gemini) Observatoire de la Côte d'Azur (Laboratoires Cassiopée et Gemini)
Tristan Guillot (PI)                         Scientific preparation, operation supervision, preparation of modelling tools, analysis of the results and scientific interpretation
Francois Fressin (IS) Scientific and technical preparation, modelling tools, analysis of the results and scientific interpretation
Alain Blazit Responsible of the camera team Developpement of test and acquisition tools.
Jean Gay Follow-up of the telescope conception Technical preparation, optical properties modelling
Yves Rabbia Telescope environment, follow-up of the telescope conception
Jean-Pierre Rivet Telescope environment, flat fielding system
Dominique Albanese Camera control softwares camera testing expertise
Laboratoire Universitaire d'Astrophysique de Nice Laboratoire Universitaire d'Astrophysique de Nice
François-Xavier Schmider Scientific and technical preparation (telescope), Dome C logistics, analysis of the results and scientific interpretation
Karim Agabi (PM) Technical preparation, Dome C logistics, telescope design and telescope control systems
Jean-Batiste Daban Technical preparation, Dome C logistics, telescope design and telescope control systems
Eric Fossat Dome C logistics, analysis of the results and scientific interpretation
Lyu Abe Quality control, tests and installation
Cécile Combier Telescope and camera control softwares
François Jeanneaux Mechanical study of the camera environment
Yan Fantei Temperature regulation system, camera control system
Observatoire Astrophysique de Marseille Provence (LAM OHP) Observatoire Astrophysique de Marseille Provence (LAM OHP)
Claire Moutou Scientific preparation, follow-up of transit candidates, photometric reduction
Magali Deleuil Scientific preparation, follow-up of transit candidates
Marc Ferrari Consulting on optical properties of the telescopes, tests and optical simulations
François Bouchy Scientific preparation, follow-up of transit candidates
Antoine Llebaria Image processing, stellar photometry
Michel Boer Responsible for providing a telescope control system based on TAROT, scientific interpretation
Hervé Le Corroler Scientific interpretation
Alain Klotz Telescope and camera control software, scientific interpretation
Auguste Le van Suu Computer interfaces, telescope control system
Jérome Eysseric System engineer
Claudine Carol Computer engineer
Observatoire de Genève Observatoire de Genève
Frédéric Pont Scientific preparation, specifications, analysis of the results, follow-up of transit candidates, scientific interpretation
Deutsches zentrum für Luft und Raumfart Deutsches zentrum für Luft und Raumfart
Anders Erikson Adaptation of the data reduction pipeline Experience with running the transit surveys BEST (OHP) and BEST II (La Silla)
Heike Rauer Scientific preparation, specifications, analysis of the results, comparison of BEST II / A STEP data
THE A STEP TEAM
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A STEP Telescope
A STEP Characteristics Camera use Defocused
PSF PSF sampling FWHM covering 4 pixel Time
exposure 10s Readout time 10s Telescope
mount German Equatorial Astrophysics 1200 With
controlled heating Pointing precision tolerated
.5 Contractor Optique et Vision ERI
CCD DW 436 (Andor) Size 2048 x 2048 Pixel size
13.5 mm 1.74 arcsec on sky
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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

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A precise photometric telescope at Dome C
Telescope tube INVAR structure With Carbon
fiber coverage
Thermal enclosure for focal instrumentation
Wynne Corrector
4Mpixel DW436 CCD
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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

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Target stellar field for first campaign
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Data processing
Re-use of the major part of BEST (Berlin
Exoplanet Search Telescope) data pipeline
(Erikson, Rauer)
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Schedule of A STEP
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Schedule of A STEP
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CoRoTlux
Stellar field generation with astrophysical noise
sources
Blends simulation
Light curves generation and transit search
algorithms coupling
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Expected results
Using CoRoTlux simulator (end to end stellar
field to light curves generator) Guillot,
Fressin, Pont, Marmier,

• Considering only planets Giant Planets (Hot
  Saturn and Jupiter)
• Simulation done with CoRoTlux considering 4
  stellar fields (1 first year, 3 second year)
• Average of 12 Giant Planets for 10 Monte-Carlo
  draws

Exemples of results of two CoRoTlux simulations
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False Transit Discrimination
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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 binaries
Triple Systems
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Blends discrimination
Within lightcurve Secondary transits Detection
level Exoplanet diagnostic or minimal
radius Tingley Sackett Ellipsoidal
variability of close binaries (Sirko Paczynski
2003) Photocenter of the fluctuation
Ground based follow-up Radial velocities
(provides confirmation by a different method AND
planet characterization) HARPS Precise
photometry with high resolution telescopes and
Adaptive optics for critical cases
-gt 70 to 90 of transit candidates could be
discriminated within lighturves (Estimation from
CoRoTlux results Fressin)
-gt99 false events discrimination goal -gt
confirmation of most transits with radial
velocities ?
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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

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Global ongoing study Simulation of the optimal
transit search program
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Why searching for transits?

• Only possible way known to measure an exoplanet
  radius
• Combined with radial velocity measurements
• Mass, density, composition
• Capacity to detect small objets
• Jupiter 1 Earth 0.01

Radius measurement (photometry)
Mass Measurement (radial velocities)
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