Tidal Tails of Star Clusters
  Based on recent findings of a formation mechanism of substructure in tidal
tails by Kuepper, Macleod & Heggie (2008) we investigate a more comprehensive
set of N-body models of star clusters on orbits about a Milky-Way-like
potential. We find that the predicted epicyclic overdensities arise in any
tidal tail no matter which orbit the cluster follows as long as the cluster
lives long enough for the overdensities to build up.
  The distance of the overdensities along the tidal tail from the cluster
centre depends for circular orbits only on the mass of the cluster and the
strength of the tidal field, and therefore decreases monotonically with time,
while for eccentric orbits the orbital motion influences the distance, causing
a periodic compression and stretching of the tails and making the distance
oscillate with time. We provide an approximation for estimating the distance of
the overdensities in this case.
  We describe an additional type of overdensity which arises in extended tidal
tails of clusters on eccentric orbits, when the acceleration of the tidal field
on the stellar stream is no longer homogeneous. Moreover, we conclude that a
pericentre passage or a disk shock is not the direct origin of an overdensity
within a tidal tail. Escape due to such tidal perturbations does not take place
immediately after the perturbation but is rather delayed and spread over the
orbit of the cluster. All observable overdensities are therefore of the
mentioned two types. In particular, we note that substructured tidal tails do
not imply the existence of dark-matter sub-structures in the haloes of
galaxies.
