The Formation of Multiple Stars

Eduardo Delgado-Donate & Cathie Clarke

We have undertaken a series of SPH hydrodynamic + N-body simulations
in order to explore the mass distribution and multiplicity properties
of young stars. Our results suggest that the IMF may be sensitive to
environment in its substellar region, with more brown dwarfs being
formed where clusters are denser or more compact. We find that
multiple stars are a natural outcome of collapsing turbulent flows,
with a high incidence of $N > 2$ multiples. We find a positive
correlation of multiplicity with primary mass but a companion
frequency that decreases with age, in accordance with observations. On
the other hand, binary brown dwarfs are rarely formed, in conflict
with observational lower limits of a 15\% fraction. Brown dwarfs as
companions are predominantly found orbiting binaries or triples at
large separations; thus we reproduce the so-called brown dwarf desert.
One caveat of these models, namely the paucity of wide low mass ratio
binaries, has been addressed with additional calculations. The resuls,
though preliminary. suggest that a combination of collapsing cores of
high specific angular momentum and a relatively isolated environment
are necessary requirements to produce a significant fraction of these
systems.