SOPHIE velocimetry of Kepler transit candidates VII. A false-positive rate of 35% for Kepler close-in giant exoplanet candidates

摘要

The false-positive probability (FPP) of Kepler transiting candidates is a keyvalue for statistical studies of candidate properties. A previous investigationof the stellar population in the Kepler field has provided an estimate for theFPP of less than 5% for most of the candidates. We report here the results ofour radial velocity observations on a sample of 46 Kepler candidates with atransit depth greater than 0.4%, orbital period less than 25 days and host starbrighter than Kepler magnitude 14.7. We used the SOPHIE spectrograph mounted onthe 1.93-m telescope at the Observatoire de Haute-Provence to establish thenature of the transiting candidates. In this sample, we found five undilutedeclipsing binaries, two brown dwarfs, six diluted eclipsing binaries, and ninenew transiting planets that complement the 11 already published planets. Theremaining 13 candidates were not followed-up or remain unsolved due to photonnoise limitation or lack of observations. From these results we computed theFPP for Kepler close-in giant candidates to be 34.8% \pm 6.5%. We aimed toinvestigate the variation of the FPP for giant candidates with the longerorbital periods and found that it should be constant for orbital periodsbetween 10 and 200 days. This significant disagrees with the previousestimates. We discuss the reasons for this discrepancy and the possibleextension of this work toward smaller planet candidates. Finally, taking thefalse-positive rate into account, we refined the occurrence rate of hotjupiters from the Kepler data.