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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)

The future of transit searches

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 searches1
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
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
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
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
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
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 f pont 2005
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
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
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

Expected results

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
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