The contribution of secondary eclipses as astrophysical false positives to exoplanet transit surveys

International audienceinvestigate the astrophysical false-positive configuration in exoplanet-transit surveys. It involves eclipsing binaries and giant planets that present only a secondary eclipse, as seen from the Earth. To test how an eclipsing binary configuration can mimic a planetary transit, we generated synthetic light curves of three examples of secondary-only eclipsing binary systems that we fit with a circular planetary model. Then, to evaluate its occurrence we modeled a population of binaries in double and triple systems based on binary statistics and occurrence. We find that 0.061% +/- 0.017% of main-sequence binary stars are secondary-only eclipsing binaries that mimics a planetary transit candidate with a size down to the size of the Earth. We then evaluate the occurrence that an occulting only giant planet can mimic an Earth-like planet or even a smaller one. We find that 0.009% +/- 0.002% of stars harbor a giant planet that only presents the secondary transit. Occulting-only giant planets mimic planets that are smaller than the Earth, and they are in the scope of space missions like Kepler and PLATO. We estimate that up to 43.1 +/- 5.6 Kepler objects of interest can be mimicked by this configuration of false positives, thereby re-evaluating the global false-positive rate of the Kepler mission from 9.4 +/- 0.9% to 11.3 +/- 1.1%. We note, however, that this new false positive scenario occurs at relatively long orbital periods compared with the median period of Kepler candidates