Search for (sub)stellar companions of exoplanet host stars

In order to determine the true impact of stellar multiplicity on the formation and on the evolution of planets, we have initiated direct imaging surveys to detect stellar but also substellar companions of exoplanet host stars on close orbits, whose gravitational impact on the planet bearing disk at first and on formed planets afterwards is expected to be maximal. According to theory these are the most challenging environments for planet formation and evolution but might occur quite frequently in the milky way, due to the large number of multiple star systems found within our galaxy. Here we will show results, obtained so far in the course of our AO and Lucky-imaging campaigns of exoplanet host stars, conducted with NACO at ESO-VLT in Chile for southern and with AstraLux at the Calar Alto Observatory in Spain for northern targets, respectively. In addition, we will introduce our new high contrast imaging survey of southern exoplanet host stars, just recently started with SPHERE at ESO-VLT, and we will present some of the latest results of this project.