The discovery of a massive white dwarf in the peculiar binary system HD 49798∕RX J0648.0–4418 (original) (raw)
Related papers
An ultramassive, fast-spinning white dwarf in a peculiar binary system
Science (New York, N.Y.), 2009
White dwarfs typically have masses in a narrow range centered at about 0.6 solar mass (M(o)). Only a few ultramassive white dwarfs (mass > 1.2 M(o)) are known. Those in binary systems are of particular interest, because a small amount of accreted mass could drive them above the Chandrasekhar limit, beyond which they become gravitationally unstable. Using data from the x-ray multimirror mission (XMM)-Newton satellite, we show that the x-ray pulsator RX J0648.0-4418 is a white dwarf with mass > 1.2 M(o), based on dynamical measurements only. This ultramassive white dwarf in a post-common envelope binary with a hot subdwarf can reach the Chandrasekhar limit, and possibly explode as a type Ia supernova, when its helium-rich companion will transfer mass at an increased rate through Roche lobe overflow.
We report on the first near-simultaneous X-ray and optical observations of RX J0806.3+1527. The source is believed to be a 321 s orbital period ultracompact binary system hosting an X-ray-emitting white dwarf. Data were obtained with Chandra and the ESO Very Large Telescope (VLT) in 2001 November. We found an optical/X-ray phase shift in the periodic modulation of about 0.5, strongly favoring the existence of two distinct emission regions in the two bands (for the pulsed fluxes). The Chandra data allow us to study, for the first time, the spectral continuum of RX J0806.3+1527 in soft X-rays. This was well fitted by a blackbody spectrum with kT~65 eV and hydrogen column density of N_H ~ 5×10^20 cm^-2. The average (unabsorbed) source 0.1-2.5 keV luminosity during the modulation-on phase is L_X ~ 5×10^32 ergs s^-1 (assuming a distance of 500 pc). Such a value is lower than the luminosity expected if stable mass transfer between two white dwarfs were driven by gravitational radiation. Evidence for absorption-like features are present in the phase-averaged spectrum at about 0.53, 0.64, and 1.26 keV, which may be attributed to heavy elements (C and N). We compare and discuss these findings with other binary systems hosting an accreting white dwarf.
The Luminous Supersoft X-Ray Source RXJ0925.7-4758 as a Binary Accreting White Dwarf
2016
The luminous super soft X-ray sources (LSSS) are believed to be white dwarf binaries with large mass accretion rates (~1×10 -7 - 6×10 -7 M Θ yr -1 ) and the energy source is the steady nuclear burning on the white dwarf (WD) surface. During such high accretion rates, hydrogen shell burning consumes hydrogen at the same rate as the WD accretes. In the present work, the LSSS RXJ0925.7-4758 has been studied to examine whether steady state nuclear burning can contribute to emit super soft X-radiation. The luminosity and effective temperature of the LSSS RXJ0925.7-4758 are calculated using the model proposed by Nomoto et.al ., 2007 and the values of luminosity (8.56x10 37 erg/sec) and effective temperature (94.19 ev) are found to tally well with the observed ones. Using formulas of Hoshi, 1998, the color temperature of the LSSS RXJ0925.7-4758 is calculated which is found to be 106 ev and it is higher than the effective temperature of the source.