Corot Week 9 ESTEC 5-9 Dec 2005 Frédéric Pont Geneva Observatory Lessons from the OGLE planetary transit 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’ mn on mv=17  S/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 (GSC Mandushev et al. 2005) Planetary transit mimics RV Light curveCMD

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.) --> ~ 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

Corot Week 9 ESTEC 5-9 Dec 2005 — magnitude dependence with white noise — magnitude dependence with red noise OGLE transit detection threshold

Corot Week 9 ESTEC 5-9 Dec 2005 Colours of noise white red pink

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 Transit detection signal-to-noise: SNR = Detection threshold: SNR > ( stat. tests) Real detection treshold and potential of transit surveys? depth  /  n OGLE-TR-131OGLE-TR-132

Corot Week 9 ESTEC 5-9 Dec 2005 SNR 2 = Transit detection significance with real photometric noise depth 2 In the regime relevant to transit surveys, the red term dominates! white noise (photon+sky+scintillation)  = 3-10 mmag, n=20-50,  2 / n = mmag 2 red noise (systematics from seeing, weather, tracking) 1/ n 2  cov(x i,x i ) = (3-5 mmag) 2 = mmag 2  2 / n + 1/ n 2  cov(x i,x i )

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 Second transiting planet around OGLE-TR-111 ?

Corot Week 9 ESTEC 5-9 Dec 2005 Application of revised yield estimates to some surveys affects also Gillon et al. 2005

Corot Week 9 ESTEC 5-9 Dec 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 ?