Potential of Photometric Searches for Transiting Planets

Many ground-based photometric surveys are now under way, and five of them have been successful at detecting transiting exoplanets. Nevertheless, detecting transiting planets has turned out to be much more challenging than initially anticipated. Transit surveys have learnt that an overwhelming number of false positives and confusion scenarios, combined with an intermittent phase coverage and systematic residuals in the photometry, could make ground-based surveys rather inefficient in the detection of transiting planets. We have set up a working group on transiting planets to confront the experience of the different surveys and get a more complete understanding of these issues, in order to improve the observing strategies and analysis schemes for ongoing surveys, and to prepare for the coming Corot and Kepler space missions. This contribution presents the current results of our working group. Enter the transiting planets, one by one Transiting planets play a fundamental role in the exploration of planets outside the Solar System. The transit lightcurve, when combined with a radial velocity orbit, gives direct access to the planet’s mean density, a fundamental physical parameter. Spectroscopy during the transit and infrared photometry of the passage of the planet behind the star have already permitted direct measurements of some spectral characteristics of the atmosphere of extrasolar gas giantsan achievement that would have sounded futuristic only a decade ago. The quest for transiting exoplanets is a nascent field. The first mass-radius diagram for hot Jupiters was published two years ago (Fig. 1), with only four hot Jupiters and considerable error bars. As of November 2006, fourteen transiting hot Jupiters are known. Indeed, the Heidelberg meeting proved extremely welltimed, with four detections announced within a month of the meeting, including two in this volume (Street et al.). For many participants, the Heidelberg workshop will have marked the transition from a period of doubts about the potential of ground-based transit surveys, to a heady anticipation on the accelerating rate of discoveries.