Corot Week 9 ESTEC 5-9 Dec 2005

Frédéric Pont

Geneva Observatory

Lessons from the OGLE planetary Lessons from the OGLE planetary transit surveytransit survey

Francois Bouchy (Marseille/OHP), Nuno Santos (Lisbon), Claudio Melo (ESO), Didier Queloz, Shay Zucker, Stephane Udry, Michel Mayor

(Geneva), Claire Moutou (Marseille)

Corot Week 9 ESTEC 5-9 Dec 2005

FLAMES : 7-fiber link to high-resolution spectro UVES on the VLT

R ~ 45’000

45 mn on mv=17S/N ~ 8 ~30 m/s

FLAMES follow-up of OGLE candidates

Field of view 25’x 25’

137 shallow transit candidates published by OGLE

60 followed in radial velocity by our team with FLAMES (15<V<18)

5 transiting planets detected

Corot Week 9 ESTEC 5-9 Dec 2005

Nature of planetary transit mimics

Eclipsing binaries

- grazing

- low-mass companion

- multiple systems and blends

False positive of the transit detection

deep transits

shallow transits

Corot Week 9 ESTEC 5-9 Dec 2005

Light curve can be

undistinguishable from planetary transit

can be impossible to discriminate from light curve

easy with high-resolution spectroscopy

II: small stellar companion

Planetary transit mimics

OGLE-TR-122b, Pont et al. 2005

Corot Week 9 ESTEC 5-9 Dec 2005

Wide range of possible scenarios

Requires global analysis, light curve + radial velocity

Often more than one component visible in the spectrum (but not always)

Triple system can also mimic planetary RV variation!

ranges from easy to very tricky to discriminate

III: multiple system or blend

OGLE-TR-33 Torres et al. 2004

(GSC 01944-02289 Mandushev et al. 2005)

Planetary transit mimics

RV

Light curve CMD

Corot Week 9 ESTEC 5-9 Dec 2005

• RV follow-up essential part of photometric transit surveys

required to establish planetary nature of Gas Giant candidates

Implications of planetary transit mimic scenarios

Corot Week 9 ESTEC 5-9 Dec 2005

What are the contaminants for super-Earth transits ?

Transiting M-dwarfs like OGLE-TR-122 will not be a problem

BUT

Gravitationally bound triple system will still be a source of mimics

(how good mimics? To be studied)

Background eclipsing binaries will be very numerous.

“CorotLux” simulator (Guillot et al.) --> ~100-200 per field

Most of these will be easy to discriminate

Corot Week 9 ESTEC 5-9 Dec 2005

Detection threshold of transit signal

Corot Week 9 ESTEC 5-9 Dec 2005

1990 1995 2000 2005 2010 2015

00001000000000000500000

Corot Week 9 ESTEC 5-9 Dec 2005

Colours of noise

white

red

pink

Corot Week 9 ESTEC 5-9 Dec 2005

Corot Week 9 ESTEC 5-9 Dec 2005

• Factor 3-5 in threshold!

• Weaker dependence on magnitude

• Steeper dependence on period

Detection threshold with red noise (systematics)

Corot Week 9 ESTEC 5-9 Dec 2005

SNR2 =

Transit detection significance with real photometric noise

depth2

In the regime relevant to transit surveys, the red term dominates!

white noise (photon+sky+scintillation)

= 3-10 mmag, n=20-50, 2 / n = 0.1 - 0.5 mmag 2

red noise (systematics from seeing, weather, tracking)

1/ n2 cov(xi,xi) = (3-5 mmag)2 = 9 - 25 mmag 2

2 / n + 1/ n2 cov(xi,xi)

Corot Week 9 ESTEC 5-9 Dec 2005

Second transiting planet around OGLE-TR-111 ?

Corot Week 9 ESTEC 5-9 Dec 2005

Application of revised yield estimates to some surveys

Survey mc HJ detectionsper season

HJ detectionwhite noise

STARE 14 0.9 (7)

OGLE 17.2 1.1 (14)

HATNet 11 0.2 (18)

Vulcan 11 0.6 (16)

UNSW 13.6 0.01 (2)

affects also Gillon et al. 2005

Corot Week 9 ESTEC 5-9 Dec 2005

- site / optics /detector / photometric reduction- covariance removal (SYS-REM, Tamuz et al. 2004)

- modify tradeoff systematics vs random error

There may be a practical limit for ground-based wide-field photometry

(due to number of comparison star compared to number of correction parameters and total variation of flux)

We find r 3 mmag for all large ongoing surveys

The hour-scale systematics of ground-based surveys:

does the atmosphere set a hard limit ?

! Detection of transiting Neptunes from ground prevented by red noise.

Corot Week 9 ESTEC 5-9 Dec 2005

COROT

r = 0.7 mmag according to Corot instrument team

r = 2.2 mmag according to realistic blind-test simulations [Moutou et al. 2005]

High predicted yield of transiting Hot Jupiters due to large time coverage

(150 x 24 hrs)

Sensitivity to Super-Earth will depend on level of actual red noise

Implications for Corot ?