The effects of dynamical interactions on planets in young substructured
  star clusters
  We present N-body simulations of young substructured star clusters undergoing
various dynamical evolutionary scenarios and examine the direct effects of
interactions in the cluster on planetary systems. We model clusters initially
in cool collapse, in virial equilibrium and expanding, and place a 1
Jupiter-mass planet at either 5au or 30au from their host stars, with zero
eccentricity. We find that after 10Myr 10% of planets initially orbiting at
30au have been liberated from their parent star and form a population of
free-floating planets. A small number of these planets are captured by other
stars. A further 10% have their orbital eccentricity significantly altered. The
change in eccentricity is often accompanied by a change in orbital inclination
which may lead to additional dynamical perturbations in planetary systems. The
fraction of liberated and disrupted planetary systems is highest for subvirial
clusters, but virial and supervirial clusters also dynamically process
planetary systems, due to interactions in the substructure. Of the planets that
become free-floating, those that remain observationally associated with the
cluster (within two half-mass radii of the cluster centre) have a similar
velocity distribution to the entire star cluster, irrespective of whether they
were on a 5au or a 30au orbit, with median velocities typically 1km/s.
Conversely, those planets that are no longer associated with the cluster have
similar velocities to the non-associated stars if they were originally at 5au
(9km/s), whereas planets originally at 30au have much lower velocities
(3.8km/s) than the stars (10.8km/s). These findings highlight potential
pitfalls of concluding that (a) planets with similar velocities to the cluster
stars represent the very low-mass end of the IMF, and (b) planets on the
periphery of a cluster with very different observed velocities form through
different mechanisms.
