Discovery of a compact companion to the hot subdwarf star BD+37 442

Abstract

We report the results of the first X-ray observation of the luminous and helium-rich O-type subdwarf BD+37 442, carried out with the XMM-Newton satellite in August 2011. X-ray emission is detected with a flux of about 3x10^(-14) erg/cm2/s (0.2-1 keV) and a very soft spectrum, well fit by the sum of a blackbody with temperature kT_BB = 45^(+11)_(-9) eV and a power law with a poorly constrained photon index. Significant pulsations with a period of 19.2 s are detected, indicating that the X-ray emission originates in a white dwarf or neutron star companion, most likely powered by accretion from the wind of BD+37 442.

5 pages, 4 figures, 1 table. Accepted for publication by The Astrophysical Journal Letters

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• Constraints on the winds of hot subdwarf stars from X-ray observations of two sdB binaries with compact companions: CD -30 11223 and PG 1232-136
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• The lack of X-ray pulsations in the extreme helium star BD+37${}^{\circ }$442 and its possible stellar wind X-ray emission
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