Implementing Primordial Binaries in Simulations of Star Cluster
  Formation with a Hybrid MHD and Direct N-Body Method
  The fraction of stars in binary systems within star clusters is important for
their evolution, but what proportion of binaries form by dynamical processes
after initial stellar accretion remains unknown. In previous work, we showed
that dynamical interactions alone produced too few low-mass binaries compared
to observations. We therefore implement an initial population of binaries in
the coupled MHD and direct N-body star cluster formation code Torch. We compare
simulations with, and without, initial binary populations and follow the
dynamical evolution of the binary population in both sets of simulations,
finding that both dynamical formation and destruction of binaries take place.
Even in the first few million years of star formation, we find that an initial
population of binaries is needed at all masses to reproduce observed binary
fractions for binaries with mass ratios above the $q \geq 0.1$ detection limit.
Our simulations also indicate that dynamical interactions in the presence of
gas during cluster formation modify the initial distributions towards binaries
with smaller primary masses, larger mass ratios, smaller semi-major axes and
larger eccentricities. Systems formed dynamically do not have the same
properties as the initial systems, and systems formed dynamically in the
presence of an initial population of binaries differ from those formed in
simulations with single stars only. Dynamical interactions during the earliest
stages of star cluster formation are important for determining the properties
of binary star systems.
