Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The non-thermal, time-variable radio emission from Cyg OB2 # 5: A
  wind-collision region   The radio emission from the well-studied massive stellar system Cyg OB2 #5 is
known to fluctuate with a period of 6.7 years between a low-flux state when the
emission is entirely of free-free origin, and a high-flux state when an
additional non-thermal component (of hitherto unknown nature) appears. In this
paper, we demonstrate that the radio flux of that non-thermal component is
steady on timescales of hours, and that its morphology is arc-like. This shows
that the non-thermal emission results from the collision between the strong
wind driven by the known contact binary in the system, and that of an unseen
companion on a somewhat eccentric orbit with a 6.7-yr period and a 5 to 10 mas
semi-major axis. Together with the previously reported wind-collision region
located about 0.8 arcsec to the north-east of the contact binary, Cyg OB2 #5
appears to be the only multiple system known so far to harbor two radio-imaged
wind-collision regions.

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The categories of this paper are: supr-con
11
The categories of this paper are: hep-lat
5
The categories of this paper are: gr-qc
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The categories of this paper are: mtrl-th
12
The categories of this paper are: nucl-th
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The categories of this paper are: cmp-lg
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The categories of this paper are: eess
10
The categories of this paper are: q-bio
16
The categories of this paper are: stat
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The categories of this paper are: atom-ph
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The categories of this paper are: ao-sci
15
The categories of this paper are: nucl-ex
0
The categories of this paper are: hep-ph
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The categories of this paper are: funct-an
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The categories of this paper are: dg-ga
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The categories of this paper are: adap-org