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

TL;DR

This paper examines how secondary eclipses in binary systems and occulting-only giant planets can mimic exoplanet transits, affecting false-positive rates in surveys like Kepler and PLATO.

Contribution

It quantifies the occurrence of secondary-only eclipsing binaries and occulting-only giant planets as false positives in exoplanet surveys, updating false-positive rate estimates.

Findings

0.061% of main-sequence binaries are secondary-only eclipsing binaries.

0.009% of stars host occulting-only giant planets mimicking smaller planets.

False-positive rate for Kepler candidates increases from 9.4% to 11.3%.

Abstract

We investigate in this paper the astrophysical false-positive configuration in exoplanet-transit surveys that involves eclipsing binaries and giant planets which present only a secondary eclipse, as seen from the Earth. To test how an eclipsing binary configuration can mimic a planetary transit, we generate synthetic light curve of three examples of secondary-only eclipsing binary systems that we fit with a circular planetary model. Then, to evaluate its occurrence we model a population of binaries in double and triple system based on binary statistics and occurrence. We find that 0.061% +/- 0.017% of main-sequence binary stars are secondary-only eclipsing binaries mimicking a planetary transit candidate 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 smaller planet. We find that 0.009% +/- 0.002% of stars harbor a giant planet that present only the secondary transit. Occulting-only giant planets mimic planets smaller than the Earth that 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 new configuration of false positives, 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 period compared with the median period of Kepler candidates.