The lack of X-ray pulsations in the extreme helium star BD+37 degree 442 and its possible stellar wind X-ray emission

We report the results of a new XMM-Newton observation of the helium-rich hot subdwarf BD+37 degree 442 carried out in 2016 February. The possible periodicity at 19 s seen in a 2011 shorter observation is not confirmed, thus dismissing the evidence for a binary nature. This implies that the observed...

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Bibliographic Details
Published in:Monthly notices of the Royal Astronomical Society 2017-04, Vol.466 (3), p.2918-2918
Main Authors: Mereghetti, Sandro, La Palombara, Nicola, Tiengo, Andrea, Esposito, Paolo
Format: Article
Language:English
Subjects:
Companion stars
Emission
Luminosity
Soft x-rays
Stars
Stellar winds
X rays
XMM (spacecraft)
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Summary:We report the results of a new XMM-Newton observation of the helium-rich hot subdwarf BD+37 degree 442 carried out in 2016 February. The possible periodicity at 19 s seen in a 2011 shorter observation is not confirmed, thus dismissing the evidence for a binary nature. This implies that the observed soft X-ray emission, with a luminosity of a few 10 super( 31) erg s super( -1), originates in BD+37 degree 442 itself, rather than in an accreting neutron star companion. The X-ray spectrum is well fit by thermal plasma emission with a temperature of 0.22 keV and non-solar element abundances. Besides the overabundance of He, C and N already known from optical/UV studies, the X-ray spectra indicate also a significant excess of Ne. The soft X-ray spectrum and the ratio of X-ray to bolometric luminosity, LX/LBOL ~ 2 x 10 super( -7), are similar to those observed in massive early-type stars. This indicates that the mechanisms responsible for plasma shock-heating can work also in the weak stellar winds (mass-loss rates MW less than or equal to 10 super( -8) M... yr super( -1)) of low-mass hot stars. (ProQuest: ... denotes formulae/symbols omitted.)
ISSN:0035-8711
1365-2966