Bayesian detection of planetary transits - A modified version of the Gregory-Loredo method for Bayesian periodic signal detection

The detection of planetary transits in stellar photometric light-curves is poised to become the main method for finding substantial numbers of terrestrial planets. The French-European mission COROT (foreseen for launch in 2005) will perform the first search on a limited number of stars, and larger missions Eddington (from ESA) and Kepler (from NASA) are planned for launch in 2007. Transit signals from terrestrial planets are small (DeltaF/F similar or equal to 10(-4)),short (Deltat similar or equal to 10 hours) dips, which repeat with periodicity of a few months, in time series lasting up to a few years. The reliable and automated detection of such signals in large numbers of light curves affected by different sources of noise is a statistical and computational challenge. We present a novel algorithm based on a Bayesian approach. The algorithm is based on the Gregory-Loredo method originally developed for the detection of pulsars in X-ray data. In the present paper the algorithm is presented, and its performance on simulated data sets dominated by photon noise is explored. In an upcoming paper the influence of additional noise sources (such as stellar activity) will be discussed.