  (abridged) Context. Wide binaries are a potential pathway for the formation
of hot Jupiters. The binary fraction among host stars is an important
discriminator between competing formation theories, but has not been well
characterised. Additionally, contaminating light from unresolved stars can
significantly affect the accuracy of photometric and spectroscopic measurements
in studies of transiting exoplanets. Aims. We observed 101 transiting exoplanet
host systems in the Southern hemisphere in order to create a homogeneous
catalogue of both bound companion stars and contaminating background stars. We
investigate the binary fraction among the host stars in order to test theories
for the formation of hot Jupiters, in an area of the sky where transiting
exoplanetary systems have not been systematically searched for stellar
companions. Methods. Lucky imaging observations from the Two Colour Instrument
on the Danish 1.54m telescope at La Silla were used to search for previously
unresolved stars at small angular separations. The separations and relative
magnitudes of all detected stars were measured. For 12 candidate companions to
10 host stars, previous astrometric measurements were used to evaluate how
likely the companions are to be physically associated. Results. We provide
measurements of 499 candidate companions within 20 arcseconds of our sample of
101 planet host stars. 51 candidates are located within 5 arcseconds of a host
star, and we provide the first published measurements for 27 of these.
Calibrations for the plate scale and colour performance of the Two Colour
Instrument are presented. Conclusions. We find that the overall multiplicity
rate of the host stars is 38 +17 -13%, consistent with the rate among
solar-type stars in our sensitivity range, suggesting that planet formation
does not preferentially occur in long period binaries compared to a random
sample of field stars.
