  We are studying the influence of stellar multiplicity on exoplanet systems,
in particular systems that have been detected via radial-velocity searches. We
are in particular interested in the closest companions as they would have a
strong influence on the evolution of the original planet forming disks. In this
study we present new companions detected during our ongoing survey of exoplanet
hosts with VLT/SPHERE. We are using the extreme adaptive optics imager SPHERE
at the ESO/VLT to search for faint (sub)stellar companions. We utilized the
classical coronagraphic imaging mode to perform a snapshot survey (3-6 min
integration time) of exoplanet host stars in the Ks-band. We detected new
stellar companions to the exoplanet host stars HD1666, HIP68468, HIP107773, and
HD109271. With an angular separation of only 0.38" (40 au of projected
separation) HIP107773 is among the closest companions found to exoplanet host
stars. The presence of the stellar companion explains the linear
radial-velocity trend seen in the system. At such a small separation the
companion likely had significant influence on the evolution of the planet
forming disk around the primary star. We find that the companion in the HD1666
system may well be responsible for the high orbit eccentricity (0.63) of the
detected Jupiter class planet, making this system one of only a few where such
a connection can be established. A cross-match with the Gaia DR2 catalog showed
furthermore that the near infrared faint companion around HD109271 had been
detected in the optical and is significantly brighter than in the near infrared
making it a white dwarf companion.
