Stars on the run: escaping from stellar clusters
  A significant proportion of Milky Way stars are born in stellar clusters,
which dissolve over time so that the members become part of the disc and halo
populations of the Galaxy. In the present work we will assume that these young
stellar clusters live mainly within the disc of the Galaxy and that they can
have primordial binary percentages ranging from 0% to as high as 70%. We have
evolved models of such clusters to an age of 4 Gyr through N-body simulations,
paying attention to the stars and binaries that escape in the process. We have
quantified the contribution of these escaping stars to the Galaxy population by
analysing their escape velocity and evolutionary stage at the moment of escape.
In this way we could analyse the mechanisms that produced these escapers,
whether evaporation through weak two- body encounters, energetic close
encounters or stellar evolution events, e.g. supernovae. In our models we found
that the percentage of primordial binaries in a star cluster does not produce
significant variations in the velocities of the stars that escape in the
velocity range of 0-20 km/s. However, in the high-velocity 20-100 km/s range
the number of escapers increased markedly as the primordial binary percentage
increased. We could also infer that dissolving stellar clusters such as those
that we have modelled can populate the Galactic halo with giant stars for which
the progenitors were stars of up to 2.4 Msun. Furthermore, choices made for the
velocity kicks of remnants do influence the production of hyper-velocity stars
- and to a lesser extent stars in the high-velocity range - but once again the
difference for the 99% of stars in the 0-20 km/s range is not significant.
