  We present the results of a survey to detect low-mass companions of UMa group
members, carried out in 2003-2006 with NACO at the ESO VLT. While many
extra-solar planets and planetary candidates have been found in close orbits
around stars by the radial velocity and the transit method, direct detections
at wider orbits are rare. The Ursa Major (UMa) group, a young stellar
association at an age of about 200-600 Myr and an average distance of 25 pc,
has not yet been addressed as a whole although its members represent a very
interesting sample to search for and characterize sub-stellar companions by
direct imaging. Our goal was to find or to provide detection limits on wide
sub-stellar companions around nearby UMa group members using high-resolution
imaging. We searched for faint companions around 20 UMa group members within 30
pc. The primaries were placed below a semi-transparent coronagraph, a rather
rarely used mode of NACO, to increase the dynamic range of the images. In most
cases, second epoch images of companion candidates were taken to check whether
they share common proper motion with the primary. Our coronagraphic images rule
out sub-stellar companions around the stars of the sample. A dynamical range of
typically 13-15 mag in the Ks band was achieved at separations beyond 3" from
the star. Candidates as faint as Ks ~ 20 were securely identified and measured.
The survey is most sensitive between separations of 100 and 200 au but only on
average because of the very different target distance. Field coverage reaches
about 650 au for the most distant targets. Most of the 200 candidates are
visible in two epochs. All of those were rejected being distant background
objects.
