  A recent study of ultra-compact dwarf galaxies (UCDs) in the Virgo cluster
revealed that some of them show faint envelopes and have measured mass-to-light
ratios of 5 and larger, which can not be explained by simple population
synthesis models. It is believed that this proves that some of the UCDs must
possess a dark matter halo and may therefore be stripped nuclei of dwarf
ellipticals rather than merged star cluster complexes. Using an efficient
N-body method we investigate if a close passage of a UCD through the central
region of the host galaxy is able to enhance the measured mass-to-light ratio
by tidal forces leaving the satellite slightly out of virial equilibrium and
thereby leading to an overestimation of its virial mass. We find this to be
possible and discuss the general problem of measuring dynamical masses for
objects that are probably interacting with their hosts.
