Astrophys. J., 737, 51 (2011/August-3)
X-ray and optical observations of the unique binary system HD 49798/RX J0648.0-4418.
MEREGHETTI S., LA PALOMBARA N., TIENGO A., PIZZOLATO F., ESPOSITO P., WOUDT P.A., ISRAEL G.L. and STELLA L.
Abstract (from CDS):
We report the results of XMM-Newton observations of HD 49798/RX J0648.0-4418, the only known X-ray binary consisting of a hot sub-dwarf and a white dwarf. The white dwarf rotates very rapidly (P = 13.2 s) and has a dynamically measured mass of 1.28±0.05 M☉. Its X-ray emission consists of a strongly pulsed, soft component, well fit by a blackbody with kTBB∼ 40 eV, accounting for most of the luminosity, and a fainter hard power-law component (photon index ∼1.6). A luminosity of ∼1032 erg/s is produced by accretion onto the white dwarf of the helium-rich matter from the wind of the companion, which is one of the few hot sub-dwarfs showing evidence of mass loss. A search for optical pulsations at the South African Astronomical Observatory 1.9 m telescope gave negative results. X-rays were also detected during the white dwarf eclipse. This emission, with luminosity 2x1030 erg/s, can be attributed to HD 49798 and represents the first detection of a hot sub-dwarf star in the X-ray band. HD 49798/RX J0648.0-4418 is a post-common-envelope binary which most likely originated from a pair of stars with masses ∼8-10 M☉. After the current He-burning phase, HD 49798 will expand and reach the Roche lobe, causing a higher accretion rate onto the white dwarf which can reach the Chandrasekhar limit. Considering the fast spin of the white dwarf, this could lead to the formation of a millisecond pulsar. Alternatively, this system could be a Type Ia supernova progenitor with the appealing characteristic of a short time delay, being the descendent of relatively massive stars.
subdwarfs - white dwarfs - X-rays: binaries
BD -32 179 is a misprint for BD -03 179.
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