Interpreting and predicting the yield of transit surveys Giant planets in the OGLE fields.pdf

a r X i v : 0 7 0 4 .1 9 1 9 v 1 [ a s t r o - p h ] 1 5 A p r 2 0 0 7 1 Introduction Extrasolar planets are now routinely discovered orbiting solar-type stars by radial velocimetry, but the discovery of tran- siting planets by photometric surveys is just beginning. Although still marginal, the late success of transit surveys has given an additional impulse to exoplanetology with the possibility to es- timate the radius, density and hence composition of extrasolar planets. Quantitatively, we know to date 206 extrasolar planets with masses below 13 MJup (e.g. Udry et al. 2007; Butler et al. 2006). Among those, a list of 14 currently known transiting planets is presented in table 1. These planets have been discovered by ra- dial velocimetry followed by photometry for 3 of them, and by photometric surveys for the remaining 11. When considering the score of projects devoted to the detec- tion of planets by transit photometry, the present harvest appears meager. The discrepancy between predictions (e.g. Horne 2001) and reality has been attributed to various factors such as: im- perfect duty cycle, a reduced number of stars for which tran- siting planets are detectable (Gould et al. 2006) and the pres- ence of correlated noises that can greatly limit the detectability of small planetary transits (Pont et al. 2006b). Several generic studies have been conducted to understand the yield of different transit surveys. Pepper Gaudi (2005) studied the optimization of transit searches as a function of the observational setup, the site properties and the planet properties. Gillon et al. (2005) an- alyzed and compared deep field surveys, considering individual stellar ranges and observation windows, but did not include the effects of stellar crowding nor time-correlated noises. Gould et al. (2006) studied the yield of OGLE survey (Udalski et al. 2002), the most successful so far in term of num- ber of transiting planets discovered, with a model populating the line of sight