Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Formation of Close Binary Systems by Dynamical Interactions and
  Orbital Decay   We present results from the first hydrodynamical star formation calculation
to demonstrate that close binary stellar systems (separations $\lsim 10$ AU)
need not be formed directly by fragmentation. Instead, a high frequency of
close binaries can be produced through a combination of dynamical interactions
in unstable multiple systems and the orbital decay of initially wider binaries.
Orbital decay may occur due to gas accretion and/or the interaction of a binary
with its circumbinary disc. These three mechanisms avoid the problems
associated with the fragmentation of optically-thick gas to form close systems
directly. They also result in a preference for close binaries to have roughly
equal-mass components because dynamical exchange interactions and the accretion
of gas with high specific angular momentum drive mass ratios towards unity.
Furthermore, due to the importance of dynamical interactions, we find that
stars with greater masses ought to have a higher frequency of close companions,
and that many close binaries ought to have wide companions. These properties
are in good agreement with the results of observational surveys.

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The categories of this paper are: bayes-an
15
The categories of this paper are: nucl-ex
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The categories of this paper are: eess
14
The categories of this paper are: math-ph
0
The categories of this paper are: hep-ph
13
The categories of this paper are: quant-ph
5
The categories of this paper are: gr-qc
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The categories of this paper are: comp-gas
4
The categories of this paper are: cond-mat
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The categories of this paper are: q-fin
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The categories of this paper are: ao-sci
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The categories of this paper are: alg-geom
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The categories of this paper are: solv-int
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The categories of this paper are: physics
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The categories of this paper are: q-alg
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The categories of this paper are: hep-ex