A lucky imaging multiplicity study of exoplanet host stars - II

The vast majority of extrasolar planets are detected by indirect detection methods such as transit monitoring and radial velocity measurements. While these methods are very successful in detecting short-periodic planets, they are mostly blind to wide sub-stellar or even stellar companions on long orbits. In our study, we present high-resolution imaging observations of 60 exoplanet hosts carried out with the lucky imaging instrument AstraLux at the Calar Alto 2.2 m telescope as well as with the new Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) high-resolution adaptive optics imager at the ESO/VLT in the case of a known companion of specific interest. Our goal is to study the influence of stellar multiplicity on the planet formation process. We detected and confirmed four previously unknown stellar companions to the exoplanet hosts HD 197037, HD 217786, Kepler-21 and Kepler-68. In addition, we detected 11 new low-mass stellar companion candidates which must still be confirmed as bound companions. We also provide new astrometric and photometric data points for the recently discovered very close binary systems WASP-76 and HD 2638. Furthermore, we show for the first time that the previously detected stellar companion to the HD 185269 system is a very low mass binary. Finally, we provide precise constraints on additional companions for all observed stars in our sample.