Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: An Optical Study of BG Geminorum: An Ellipsoidal Binary with an Unseen
  Primar Star   We describe optical photometric and spectroscopic observations of the bright
variable BG Geminorum. Optical photometry shows a pronounced ellipsoidal
variation of the K0 I secondary, with amplitudes of ~0.5 mag at VRI and a
period of 91.645 days. A deep primary eclipse is visible for wavelengths <
4400A; a shallower secondary eclipse is present at longer wavelengths. Eclipse
timings and the radial velocity curve of the K0 secondary star indicate an
interacting binary where a lobe-filling secondary, M_2 ~ 0.5 Msun, transfers
material into a extended disk around a massive primary, M_1 ~ 4.5 Msun. The
primary star is either an early B-type star or a black hole. If it did contain
a black hole, BG Gem would be the longest period black hole binary known by a
factor of 10, as well as the only eclipsing black hole binary system.

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The categories of this paper are: adap-org
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The categories of this paper are: dg-ga
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The categories of this paper are: funct-an
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The categories of this paper are: comp-gas
31
The categories of this paper are: ao-sci
12
The categories of this paper are: nucl-th
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The categories of this paper are: nlin
3
The categories of this paper are: physics
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The categories of this paper are: chao-dyn
0
The categories of this paper are: hep-ph
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The categories of this paper are: cmp-lg
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The categories of this paper are: q-fin
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The categories of this paper are: mtrl-th
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The categories of this paper are: hep-lat
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The categories of this paper are: atom-ph
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The categories of this paper are: acc-phys