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Register a new userFUV Spectroscopy of the Supersoft X-ray Binary RX J0513.9-6951
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We have obtained spectroscopy with the Far Ultraviolet Spectroscopic Explorer (FUSE) of the supersoft X-ray binary RX J0513.9-6951 over a complete binary orbital cycle. The spectra show a hot continuum with extremely broad O VI emission and weak Lyman absorptions. He II emission is weak and narrow, while N III and C III emissions are undetected, although lines from these ions are prominent at optical wavelengths. The broad O VI emission and Lyman absorption show radial velocity curves that are approximately antiphased and have semiamplitudes of ~117 +- 40 and 54 +- 10 km/s, respectively. Narrow emissions from He II and O VI show small velocity variations with phasing different from the broad O VI, but consistent with the optical line peaks. We also measure considerable changes in the FUV continuum and O VI emission line flux. We discuss the possible causes of the measured variations and a tentative binary interpretation.
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We have analyzed nearly eight years of MACHO optical photometry of the supersoft X-ray binary RX J0513.9-6951 and derived a revised orbital period and ephemeris. Previously published velocities are reinterpreted using the new ephemeris. We show that the spectroscopic characteristics of the system depend strongly on whether the system is in a high or low optical state. We also discuss the properties of the sources high/low optical states and its long-term light curve. Evidence for a 83.3-day periodicity in the photometry is presented.
The supersoft X-ray binary RX J0513.9-6951 shows cyclic changes between optical-low / X-ray-on states and optical-high / X-ray-off states. It is supposed to be accreting close to the Eddington-critical limit and driven by accretion wind evolution. We seek to derive the variations in the characteristic time scales of the long-term optical light curve and to determine the implications for the physical parameters of the system. We used existing and new optical monitoring observations covering a total time span of 14 years and compared the durations of the low and high states with the model calculations of Hachisu & Kato. The cycle lengths and especially the durations of the optical high states show a longterm modulation with variations that, according to the accretion wind evolution model, would imply variations in the mass transfer rate by a factor of 5 on timescales of years.
The highly luminous (> 10^37 erg s^-1) supersoft X-ray sources (SSS) are believed to be Eddington limited accreting white dwarfs undergoing surface hydrogen burning. The current paradigm for SSS involves thermally unstable mass transfer from a 1-2 solar mass companion. However this model has never been directly confirmed and yet is crucial for the evolution of cataclysmic variables in general, and for the establishment of SSS as progenitors of type Ia supernovae in particular. The key SSS is RX J0513.9-6951 which has recurrent X-ray outbursts every 100-200 d (lasting for ~40 d) during which the optical declines by 1 mag. We present the first XMM-Newton observations of RX J0513.9-6951 through one of its optical low states. Our results show that as the optical low state progresses the temperature and the X-ray luminosity decrease, behaviour that is anti-correlated with the optical and UV emission. We find that as the optical (and UV) intensity recover the radius implied by the spectral fits increases. The high resolution spectra show evidence of deep absorption features which vary during the optical low state. Our results are consistent with the predictions of the white dwarf photospheric contraction model proposed by Southwell et al. 1996.
FUSE observations were obtained in July 2003 during 1.2 cycles of the 0.76-day binary orbit of RX J0513.9-6951. Radial velocity measurements of the broad O VI emission profile show a semiamplitude of K~26 km/sec, which is much smaller than the value of 117 km/sec measured from 2001 FUSE data. Narrow O VI emissions show no measurable velocity variation. The mean velocity of the broad O VI emission is red-shifted by ~500 km/sec with respect to both the systemic and narrow emission-line velocities. Spectral difference plots show phase-related changes in the broad emission profile. Other phase-related changes such as line and continuum variations are also smaller than in the 2001 spectra. We describe a moving broad absorption feature near 1020A as possible O VI outflow associated with a precessing jet. We discuss the implications for the stellar masses if the 2003 broad O VI velocities outline the compact stars orbital motion.
We report the discovery of an extremely close white dwarf plus F dwarf main-sequence star in a 12 hour binary identified by combining data from the RAdial Velocity Experiment (RAVE) survey and the Galaxy Evolution Explorer (GALEX) survey. A combination of spectral energy distribution fitting and optical and Hubble Space Telescope ultraviolet spectroscopy allowed us to place fairly precise constraints on the physical parameters of the binary. The system, TYC 6760-497-1, consists of a hot Teff~20,000K, M~0.6Ms white dwarf and an F8 star (M~1.23Ms, R~1.3Rs) seen at a low inclination (i~37 deg). The system is likely the descendent of a binary that contained the F star and a ~2Ms A-type star that filled its Roche-lobe on the thermally pulsating asymptotic giant branch, initiating a common envelope phase. The F star is extremely close to Roche-lobe filling and there is likely to be a short phase of thermal timescale mass-transfer onto the white dwarf during which stable hydrogen burning occurs. During this phase it will grow in mass by up to 20 per cent, until the mass ratio reaches close to unity, at which point it will appear as a standard cataclysmic variable star. Therefore, TYC 6760-497-1 is the first known progenitor of a super-soft source system, but will not undergo a supernova Ia explosion. Once an accurate distance to the system is determined by Gaia, we will be able to place very tight constraints on the stellar and binary parameters.
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