RX J0513.9−6951: THE FIRST EXAMPLE OF ACCRETION WIND EVOLUTION, A KEY EVOLUTIONARY PROCESS TO TYPE Ia SUPERNOVAE

A new self-sustained model for long-term light curve variations of RX J0513.9−6951 is proposed based on an optically thick wind model of mass-accreting white dwarfs (WDs). When the mass accretion rate to a WD exceeds the critical rate of ∼ 1×10M⊙ yr , 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 atop the WD at the critical rate. The excess matter transferred to the WD above the critical rate is expelled by winds. This is called the 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 off the very surface layer of the secondary. The matter stripped-off is lost from the binary system. Properly formulating this mass stripping effect and the ensuing decay of mass transfer rate, we are able to reproduce, in a self-sustained manner, the transition between the optical high/X-ray off and optical low/X-ray on states of RX J0513.9−6951. Thus RX J0513.9−6951 is the first example of the accretion wind evolution, which is a key evolutionary process in a recently developed evolutionary path to Type Ia supernovae. Subject headings: binaries: close — novae, cataclysmic variables — stars: individual (RX J0513.9−6951) — stars: winds, outflows — X-rays: stars