  Observed properties of stars and planets in binary/multiple star systems
provide clues to planet formation and evolution. We extended our survey for
visual stellar companions to the hosts of transiting exoplanets by 21 stars,
using the Lucky Imaging technique with the two AstraLux instruments: AstraLux
Norte at the Calar Alto 2.2-m telescope, and AstraLux Sur at the ESO 3.5-m New
Technology Telescope at La Silla. We present observations of two previously
unknown binary candidate companions, to the transiting planet host stars
HAT-P-8 and WASP-12, and derive photometric and astrometric properties of the
companion candidates. The common proper motions of the previously discovered
candidate companions with the exoplanet host stars TrES-4 and WASP-2 are
confirmed from follow-up observations. A Bayesian statistical analysis of 31
transiting exoplanet host stars observed with AstraLux suggests that the
companion star fraction of planet hosts is not significantly different from
that of solar-type field stars, but that the binary separation is on average
larger for planet host stars.
