Phase mixing due to the Galactic potential: steps in the position and
  velocity distributions of popped star clusters
  As star clusters are expected to form with low star formation efficiencies,
the gas in the cluster is expelled quickly and early in their development: the
star cluster "pops." This leads to an unbound stellar system, evolving in the
Galactic potential. Previous N-body simulations have demonstrated the existence
of a stepped number density distribution of cluster stars after popping, both
in vertical position and vertical velocity, with a passing resemblance to a
Christmas tree. Using numerical and analytical methods, we investigate the
source of this structure, which arises due to the phase mixing of the
out-of-equilibrium stellar system, determined entirely by the background
analytic potential. Considering only the vertical motions, we construct a
theoretical model to describe the time evolution of the phase space
distribution of stars in a Miyamoto-Nagai disk potential and a full Milky-Way
type potential comprising bulge, halo and disk components, which is then
compared with N-body simulations. Using our theoretical model, we investigate
the possible observational signatures and the feasibility of detection.
