Disentangling Blended K2 Photometry: Determining the Planetary Host Star

Abstract

The presence of companion stars, whether bound or unbound, make correct identification of the planetary hosting star difficult when a planet has been detected through a photometrically blended transiting event. We present an approach that uses a combination of light curve analysis and stellar modeling to disentangle eight K2 photometrically blended binary systems that have either a confirmed or suspected planet to identify the probable host star. The key to our approach is the use of the mean stellar density, calculated using the transit geometry, as a discriminator. The approach is strongly dependent on the difference in magnitude between the stars and the observed transit depth, which is corrected by the flux ratio between the two stars. While our approach does not lead to a definitive result for all systems, we were able to determine the following for the eight systems in this case study: there are two systems where the primary was highly likely to be the planet-hosting star (>90% likelihood); three systems where the primary was likely to be the hosting star (>55% likelihood); one system where the secondary was likely to be the planet-hosting star (>55% likelihood); and two systems where we were uncertain which star was the planet-hosting star (≈50% likelihood to be either the primary or the secondary). Two systems, denoted by their EPIC number, EPIC 201546283 and EPIC 201862715, had confirmed planets, K2-27b and K2-94b, respectively, with radii of 4.0 ± 0.1 and 16.4 ± 2.9 R⊕, respectively.