A STEP Expected Yield of Planets … Survey strategy The CoRoTlux Code Understanding transit survey results Fressin, Guillot, Morello, Pont

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 Transit spectroscopy offers additional possibilities not accessible for “normal” planets examples: A correlation between the metallicity of stars and planets (Guillot et al. A&A 2006) Stellar formation model constraints (Sato et al 2005) We foresee that exoplanetology will have as its core the study of transiting exoplanets

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

- Real number of “transitable” stars - Star crowding and spatial sampling effects on differential photometry - Time correlated noise sources or Red Noise - Magnitude-limited and time consuming follow- up of planetary candidates Understanding transit survey results

Observation strategy Fields of view scheduled - Single field constant following for first campaign (90 days – polar winter 2008) - Alternate fields for campaigns Target stars : all main-sequences stars with magnitude-range : in R band spectral type : F0 to M9

Target stellar field for first campaign A STEP - 1 target field

Target stellar field for first campaign Possibility to alternate different fields for following observation campaigns

CoRoTlux: from Stellar Field Generation to Transit Search Simulation and Analysis T. Guillot, F. Fressin, V. Morello, A. Garnier (OCA) F. Pont, M. Marmier (Geneva) Thanks to C. Moutou, S. Aigrain, N. Santos

CoRoTlux Stellar field generation with astrophysical noise sources Light curves generation and transit search algorithms coupling Blends simulation

The 3 goals of CoRoTlux Survey strategy / Estimation of Transit search efficiency Estimation of different contamination sources and blends -> Characterization of follow up needs Understanding of real light curves / survey analysis

Stellar field generation : Combination of - real stellar counts (as a function of mag and stellar type) when available -Besancon model of the galaxy for stellar characteristics - Geneva-Copenhagen distribution for metallicity (Nordström et al) Double and triple systems Background stars generated up to magnitude = (faintest targets mag) + 5

Planetary distribution/characteristics: Considering only giant planets (mass over 0.3 MJ) Based on planets discovered by radial velocimetry Metallicity-linked distribution (Fischer-Valenti 2003., Santos 2006)

Planetary radius … Use of Tristan’s model of planetary evolution (linked to stellar irradiation, mass of the planet, and mass of its core – function of stellar metallicity Guillot 2006 )  Anti correlation between radius and host star metallicity

Event detectability CoRoTlux takes into account the different astrophysical noise sources (contamination, blends) But it does not compute environmental, instrumental, atmospheric noise sources. We consider a level of white noise and a level of correlated noise for a given survey – Pont 2006 In this simulation :  r = 3 mmag Sr = 9 as detection threshold

Free parameters and hypotheses 2 free parameters: - planetary distribution as a function of stellar type (unknown from G-stars biased RV surveys) - distribution of “Very Hot Jupiter” planets, undiscovered by RV up to date 2 subsets for planetary distribution to reproduce OGLE results: metallicity bellow or over  OGLE results indicate that low metallicity stars are unlikely to have close-in planets

average of 4.1 planets on 50 OGLE campaigns in good agreement with - stellar metallicity - stellar type - period (Very Hot Jupiter – Stroboscopic planets) - transit depth (directly linked to,planet radius) Simulations of OGLE survey to validate CoRoTlux and its hypotheses Simulation of 20 x OGLE combined campaigns

… and A STEP expectations First goals of A STEP are: - To know how precise a wide-field differential-photometry survey could be at Dome C - To qualify the site for this kind of survey with a simple instrument We thus focus on following a single stellar field during all winter for first campaign ~1.5 planets for a 90 days survey Results of 60 single field continuous campaigns

… and A STEP expectations Average number of planets found for : 1 month single-field coverage 3 months 8hours in a row/24 3 months with 3 alternate fields (15 minutes on each field in a row) – if technically mastered 3 months single-field with red noise lowered to 2 mmag A STEP 3 years campaign 30 cm telescope A STEP 3 years campaign 40 cm telescope ~ 0.9 ~ 0.7 ~ 4.2 ~ 2.2 ~10.1 ~14.8

Conclusions CoRoTlux is a useful device : - to prepair incoming transit campaigns - to qualify follow-up needs - to analyse the survey’s results A STEP should have higher returns than other ground based surveys … comparable with space ? What will be the future of transit search – cornerstone of exoplanetology ? – Which combination of telescope(s) at Dome C ?

synthetic population of targets (Besancon model, real targets) expected noise + stellar variability influence zone of background stars simulated light curves transit detection algorithm and/or detection criteria list of transit candidates type of follow-up needed, object-by-object estimate of amount and type of ground-based observations needed stellar companion, triple systems, planets from OGLE follow-up and Blind Test 2 CoRoTlux