  To understand the influence of additional wide stellar companions on planet
formation, it is necessary to determine the fraction of multiple stellar
systems amongst the known extrasolar planet population. We target recently
discovered radial velocity exoplanetary systems observable from the northern
hemisphere and with sufficiently high proper motion to detect stellar
companions via direct imaging. We utilize the Calar Alto 2.2m telescope in
combination with its lucky imaging camera AstraLux. 71 planet host stars have
been observed so far, yielding one new low-mass (0.239 \pm 0.022M\odot) stellar
companion, 4.5 arcsec (227AU of projected separation) northeast of the planet
host star HD185269, detected via astrometry with AstraLux. We also present
follow-up astrometry on three previously discovered stellar companions, showing
for the first time common proper motion of the 0.5 arcsec companion to
HD126614. Additionally, we determined the achieved detection limits for all
targets, which allows us to characterize the detection space of possible
further companions of these stars.
