The Formation and Evolution of Wide-Orbit Stellar Multiples In
  Magnetized Clouds
  Stars rarely form in isolation. Nearly half of the stars in the Milky Way
have a companion, and this fraction increases in star-forming regions. However,
why some dense cores and filaments form bound pairs while others form single
stars remains unclear. We present a set of three-dimensional,
gravo-magnetohydrodynamic simulations of turbulent star-forming clouds, aimed
at understanding the formation and evolution of multiple-star systems formed
through large scale (>~$10^3$ AU) turbulent fragmentation. We investigate three
global magnetic field strengths, with global mass-to-flux ratios of
$\mu_\phi$=2, 8, and 32. The initial separations of protostars in multiples
depends on the global magnetic field strength, with stronger magnetic fields
(e.g., $\mu_\phi$=2) suppressing fragmentation on smaller scales. The overall
multiplicity fraction (MF) is between 0.4-0.6 for our strong and intermediate
magnetic field strengths, which is in agreement with observations. The weak
field case has a lower fraction. The MF is relatively constant throughout the
simulations, even though stellar densities increase as collapse continues.
While the MF rarely exceeds 60% in all three simulations, over 80% of all
protostars are part of a binary system at some point. We additionally find that
the distribution of binary spin mis-alignment angles is consistent with a
randomized distribution. In all three simulations, several binaries originate
with wide separations and dynamically evolve to <~ $10^2$ AU separations. We
show that a simple model of mass accretion and dynamical friction with the gas
can explain this orbital evolution.
