Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: NGC 6231: X-ray properties of the early-type star population   Based on a deep XMM-Newton observation of the young open cluster NGC 6231, we
derive the main X-ray properties of its early-type star population. Among the
610 X-ray sources detected in the field, 42 are associated with early-type
stars. We investigate their $L_\mathrm{X} / L_\mathrm{bol}$ relationship and we
confirm the clear dichotomy between O- and B-type stars. The cut-off line
between the two behaviours occurs at $L_\mathrm{bol} \sim 10^{38}$ erg s$^{-1}$
as previously proposed by \citet{BSC97}. The distinction between single and
binary stars is not clear cut, except for the colliding wind system HD 152248.
The X-ray detected B-stars in NGC 6231 appear to be more luminous than
predicted from the \citeauthor{BSC97} relation. Though this suggests a bimodal
distribution of the B-star X-ray emission, we caution however that these
results might be biased by detection limits. Finally we investigate the X-ray
variability of the detected sources and we find that about 40% of the X-ray
emitters in the field of view present consistent signs of variability in the
EPIC instruments. This fraction is much larger than previously thought. About
one third of the early-type stars population, either singles or binaries,
further shows variability. These variations do not seem to be exclusively
related to binarity and could thus not be systematically interpreted in the
framework of a wind-wind collision phenomenon.

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The categories of this paper are: adap-org
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The categories of this paper are: eess
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The categories of this paper are: hep-lat
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The categories of this paper are: hep-ex
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The categories of this paper are: nucl-th
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The categories of this paper are: cs
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The categories of this paper are: econ
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The categories of this paper are: hep-th
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The categories of this paper are: supr-con
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The categories of this paper are: solv-int
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The categories of this paper are: nlin
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The categories of this paper are: quant-ph
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The categories of this paper are: math-ph
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The categories of this paper are: patt-sol
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The categories of this paper are: atom-ph
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The categories of this paper are: cond-mat