Interpreting and predicting the yield of transit surveys: giant planets in the OGLE fields

¹ Observatoire de la Côte d'Azur, Laboratoire Gemini, CNRS UMR 6203, BP 4229, 06304 Nice Cedex 4, France e-mail: fressin@obs-nice.fr
² Observatoire de la Côte d'Azur, Laboratoire Cassiopée, CNRS UMR 6202, BP 4229, 06304 Nice Cedex 4, France
³ Geneva University Observatory, Switzerland

Received: 19 January 2007
Accepted: 8 April 2007

Abstract

Transiting extrasolar planets are now discovered jointly by photometric surveys and by radial velocimetry, allowing measurements of their radius and mass. We want to determine whether the different data sets are compatible between themselves and with models of the evolution of extrasolar planets. We further want to determine whether to expect a population of dense Jupiter-mass planets to be detected by future more sensitive transit surveys. We directly simulate a population of stars corresponding to the OGLE transit survey and assign them planetary companions based on a list of 153 extrasolar planets discovered by radial velocimetry. We use a model of the evolution and structure of giant planets that assumes that they are made of hydrogen and helium and of a variable fraction of heavy elements (between 0 and 100 ). The output list of detectable planets of the simulations is compared to the real detections. We confirm that the radial velocimetry and photometric survey data sets are compatible within the statistical errors, assuming that planets with periods between 1 and 2 days are approximately 5 times less frequent than planets with periods between 2 and 5 days. We show that evolution models fitting present observational constraints predict a lack of small giant planets with large masses. As a side result of the study, we identify two distinct populations of planets: those with short periods ( d), which are found in orbit only around metal-rich stars with [Fe/H]>~-0.07, and those on longer orbits ( d), for which the metallicity bias is less marked. We further confirm the relative absence of low-mass giant planets at small orbital distances. Testing these results and the underlying planetary evolution models requires the detection of a statistically significant number of transiting planets, which should be provided over the next few years by continued ground-based photometric surveys, the space missions CoRoT and Kepler, and combined radial velocity measurements.