We report on the results we obtained with XMM observations of HD 49798 and BD +37° 442, the only two sdO stars for which X-ray emission has been observed so far. HD 49798 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 M_{⊙}, 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.
Observations of the Unique X-ray Emitting Subdwarf Stars HD 49798 and BD +37° 442
Tiengo A;Esposito P.;
2013-01-01
Abstract
We report on the results we obtained with XMM observations of HD 49798 and BD +37° 442, the only two sdO stars for which X-ray emission has been observed so far. HD 49798 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 M_{⊙}, 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.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
