The Formation and Evolution of Wide-Orbit Stellar Multiples In Magnetized Clouds. (arXiv:1911.07863v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Lee_A/0/1/0/all/0/1">Aaron T. Lee</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Offner_S/0/1/0/all/0/1">Stella S. R. Offner</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kratter_K/0/1/0/all/0/1">Kaitlin M. Kratter</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Smullen_R/0/1/0/all/0/1">Rachel A. Smullen</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Li_P/0/1/0/all/0/1">Pak Shing Li</a>
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.
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.
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