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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)

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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)

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

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


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 accessible for “normal” planets

  • 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

  • Natural but costly

  • Limited in telescope size, number of instruments...

  • from DOME C

  • Promising but uncertain

  • Requires precursor mission(s)

Why transit searches at Dome C? accessible for “normal” planets

  • 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 accessible for “normal” planets

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.

A STEP: the philosophy behind accessible for “normal” planets

  • 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 accessible for “normal” planets

10 transiting planets discovered up to date

  • 4 radial velocities + photometric follow up

  • 5 OGLE

  • 1 STARE/TrES

Transits photometry – Any problem ? accessible for “normal” planets

A huge difference between the expected number of detections and reality :







Number of detections expected per season






Real number of detections






Simulation considering « systematic effects »







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 accessible for “normal” planets(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

With a “classical” survey, only the “stroboscopic” planets are detectable !

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


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


  • Differential dilatations

    inside the telescope

  • Telescope mounts

    missfunctionning at

    really low temperature

THE campaigns (2)



A STEP Telescope campaigns (2)

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”


Optique et Vision


CCD DW 436 (Andor)

Size 2048 x 2048

Pixel size 13.5 mm

1.74 arcsec on sky

A STEP Camera : Andor DW436 campaigns (2)

  • 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 campaigns (2)

Telescope tube:

INVAR structure

With Carbon fiber coverage

Thermal enclosure for

focal instrumentation

4Mpixel DW436 CCD

Wynne Corrector

Mode of operation campaigns (2)

  • 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

Data processing campaigns (2)

Re-use of the major part of BEST

(Berlin Exoplanet Search Telescope)

data pipeline (Erikson, Rauer)

Schedule of A STEP

Schedule of A STEP campaigns (2)

CoRoTlux campaigns (2)

Stellar field generation

with astrophysical noise sources

Blends simulation

Light curves generation

and transit search algorithms coupling

Transit Depth campaigns (2)

Transit Depth

  • 12 13 14 15 16 17

  • Stellar Magnitude

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

False Transit campaigns (2)


Many events mimic transits … ! campaigns (2)

Number of events for 1 CoRoT CCD CoRoTlux (Guillot et al.)

Grazing Eclipsing Binaries


eclipsing binaries

M Dwarfs





Triple Systems



Blends discrimination campaigns (2)

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

-> 70 to 90 % of transit candidates could be discriminated within lighturves

(Estimation from CoRoTlux results – Fressin)

->99+ % false events discrimination goal

-> confirmation of most transits with radial velocities … ?

Conclusions campaigns (2)

  • 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

COROTLUX campaigns (2)

->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)

Global ongoing study:

Simulation of the optimal transit search program

Why searching for transits? campaigns (2)

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


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