Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: What Sets the Initial Rotation Rates of Massive Stars?   The physical mechanisms that set the initial rotation rates in massive stars
are a crucial unknown in current star formation theory. Observations of young,
massive stars provide evidence that they form in a similar fashion to their
low-mass counterparts. The magnetic coupling between a star and its accretion
disk may be sufficient to spin down low-mass pre-main sequence (PMS) stars to
well below breakup at the end stage of their formation when the accretion rate
is low. However, we show that these magnetic torques are insufficient to spin
down massive PMS stars due to their short formation times and high accretion
rates. We develop a model for the angular momentum evolution of stars over a
wide range in mass, considering both magnetic and gravitational torques. We
find that magnetic torques are unable to spin down either low or high mass
stars during the main accretion phase, and that massive stars cannot be spun
down significantly by magnetic torques during the end stage of their formation
either. Spin-down occurs only if massive stars' disk lifetimes are
substantially longer or their magnetic fields are much stronger than current
observations suggest.

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The categories of this paper are: atom-ph
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The categories of this paper are: comp-gas
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The categories of this paper are: supr-con
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The categories of this paper are: cmp-lg
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The categories of this paper are: nucl-ex
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The categories of this paper are: gr-qc
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The categories of this paper are: hep-ex
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The categories of this paper are: hep-th
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The categories of this paper are: stat
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The categories of this paper are: math
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The categories of this paper are: dg-ga
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The categories of this paper are: nucl-th
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The categories of this paper are: q-alg
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The categories of this paper are: mtrl-th
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The categories of this paper are: funct-an
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The categories of this paper are: econ