RX J0513.9-6951 and V Sagittae: Accretion Wind Evolution, A Key Evolutionary Process to Type IA Supernovae

Abstract

AbstractA new self-sustained model for long-term light-curve variations of the supersoft X-ray sources RX J0513.9–6951 and V Sge is proposed based on an optically thick wind model of mass-accreting white dwarfs (WDs). When the mass accretion rale to a WD exceeds the critical rate of ~ 1 x 10–1M⊙. yr–1, optically thick strong winds begin to blow from the WD so that a formation of common envelope is avoided. The WD can accrete and burn hydrogen-rich matter on the surface of the WD at the critical rate. The excess matter transferred to the WD above the critical rate is expelled by winds. This is called “accretion wind evolution.” This ejection process, however, occurs intermittently because the mass transfer is attenuated by strong winds: the strong winds collide with the secondary surface and strip oil the surface layer of the secondary. Properly formulating the mass-stripping effect and the ensuing decay of mass-transfer rate, we are able to reproduce the transition between the optical high/X-ray off and optical low/X-ray -on states of the supersoft X-ray sources RX J0513.9–6951 and V Sge. Thus these two objects are the lirst examples of accretion wind evolution, which is a key evolutionary process in a recently developed evolutionary path to Type la supernovae.