Binarity of transit host stars

Abstract

<i>Context. <i/>Straight-forward derivation of planetary parameters can only be achieved in transiting planetary systems. However, planetary attributes such as radius and mass strongly depend on stellar host parameters. Discovering a transit host star to be multiple leads to a necessary revision of the derived stellar and planetary parameters.<i>Aims. <i/>Based on our observations of 14 transiting exoplanet hosts, we derive parameters of the individual components of three transit host stars (WASP-2, TrES-2, and TrES-4) which we detected to be binaries. Two of these have not been known to be multiple before. Parameters of the corresponding exoplanets are revised.<i>Methods. <i/>High-resolution “Lucky Imaging” with AstraLux at the 2.2 m Calar Alto telescope provided near diffraction limited images in <i>i'<i/> and <i>z'<i/> passbands. These results have been combined with existing planetary data in order to recalibrate planetary attributes.<i>Results. <i/>Despite the faintness (<i>Δ<i/>mag ~ 4) of the discovered stellar companions to TrES-2, TrES-4, and WASP-2, light-curve deduced parameters change by up to more than 1<i>σ<i/>. We discuss a possible relation between binary separation and planetary properties, which – if confirmed – could hint at the influence of binarity on the planet formation process.