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

A. Santerne, F. Fressin, R. F. DÝaz, P. Figueira, J.-M. Almenara, N. C. Santos

Abstract
We investigate 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 occultingonly 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.

Keywords
planetary systems – techniques: photometric – binaries: eclipsing

Astronomy and Astrophysics
Volume 557, Number of pages A139_1
2013 September

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Instituto de Astrof├şsica e Ci├¬ncias do Espa├žo Universidade do Porto Faculdade de Ciências da Universidade de Lisboa Funda├ž├úo para a Ci├¬ncia e a Tecnologia
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