  Dwarf satellite galaxies undergo strong tidal forces produced by the main
galaxy potential. These forces disturb the satellite, producing asymmetries in
its stellar distribution, tidal tail formation, and modifications of the
velocity dispersions profiles. Most of these features are observed in the Ursa
Minor (UMi) dwarf spheroidal galaxy, which is one of the closest satellites of
the Milky Way. These features show that UMi is been tidally disrupted and
probably not in virial equilibrium. The high velocity dispersion of UMi could
also be a reflection of this tidal disruption and not the signature of the
large dark matter content that would be deduced if virial equilibrium is
assumed. In order to avoid the uncertainty produced when virial equilibrium is
assumed in systems in strong tidal fields, we present a new method of
calculating the mass-to-luminosity ratio of disrupted dwarf galaxies. This
method is based on numerical simulations and only takes into account the shape
of the dwarf density profile and the tidal tail brightness, but does not depend
on the kinematics of the dwarf. Applying this method to UMi, we obtain a
mass-to-luminosity relation of 12, which is lower than the value obtained
assuming virial equilibrium (M/L=60). In addition, if UMi has a large
dark-matter content, it will be impossible to reproduce a tidal tail as
luminous as the one observed.
