Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Observations of the unique X-ray emitting subdwarf stars HD49798 and
  BD+37 442   We report on the results we obtained with XMM-Newton observations of HD49798
and BD+37 442, the only two sdO stars for which X-ray emission has been
observed so far. HD is a single-lined spectroscopic binary with orbital period
of 1.5 days. We could establish that its companion is a massive white dwarf
with M = 1.28 Msun, which makes it a candidate type Ia supernova progenitor; we
also detected a significant X-ray emission during the white-dwarf eclipse,
which could be X-ray emission of the sdO star itself. In the case of BD+37 442,
a luminous He-rich sdO that up to now was believed to be a single star, we
discovered soft X-ray emission with a periodicity of 19.2 s. This indicates
that also this hot subdwarf has a compact binary companion, either a white
dwarf or a neutron star, most likely powered by accretion from the wind of the
sdO star.

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The categories of this paper are: mtrl-th
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The categories of this paper are: q-alg
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The categories of this paper are: gr-qc
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The categories of this paper are: math-ph
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The categories of this paper are: comp-gas
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The categories of this paper are: chem-ph
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The categories of this paper are: ao-sci
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The categories of this paper are: acc-phys
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The categories of this paper are: q-fin
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The categories of this paper are: hep-ph
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The categories of this paper are: eess
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The categories of this paper are: alg-geom
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The categories of this paper are: dg-ga
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The categories of this paper are: chao-dyn
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The categories of this paper are: stat
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The categories of this paper are: bayes-an