NGC 147, NGC 185 and CassII: a genetic approach to orbital properties,
  star formation and tidal debris
  NGC147, NGC185 and CassiopeiaII (CassII) have similar positions in the sky,
distances and measured line of sight velocities. This proximity in phase space
suggests that these three satellites of M31 form a subgroup within the Local
Group. Nevertheless, the differences in their star formation history and
interstellar medium, and the recent discovery of a stellar stream in NGC~147,
combined with the lack of tidal features in the other two satellites, are all
indications of complex and diverse interactions between M31 and these three
satellites. We use a genetic algorithm to explore the different orbits that
these satellites can have and select six sets of orbits that could best explain
the observational features of the NGC147, NGC185 and CassII satellites. The
parameters of these orbits are then used as a starting point for N-body
simulations. We present models for which NGC147, NGC185 and CassII are a bound
group for a total time of at least one Gyr but still undergo different
interactions with M31 and as a result NGC147 has a clear stellar stream whereas
the other two satellites have no significant tidal features. This result shows
that it is possible to find solutions that reproduce the contrasting properties
of the satellites and for which NGC147-NGC185-CassII have been gravitationally
bound.
