Modeling the Evolutionary Paths to Type Ia Supernovae

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We have proposed tow evolutionary paths to Type la supernovae (Sne Ia) based on our optically thick wind model of mass accreting white dwarfs. In the first year of my research (1999), we have found that white dwarfs begin to blow strong winds and when the mass accretion rate exceeds the critical rate, thus preventing the binary from collapsing. The binary does not spiral-in but keeps its separation. We call this accretion wind evolution instead of common envelope evolution.Based on the new mechanism of accretion wind evolution, we have found two paths to Sne Ia (Hachisu et al. 1999). In these two paths, white dwarfs can accrete mass continuously from the companion and grow at a rate of about one millionth of solar masses per year. Therefore, candidates for SN la progenitors are systems at the final stages on these paths ; i.e., one is a supersoft X-ray source (SSS) consisting of a white dwarf and a lobe-filling, more massive, main-sequence star and the other is a symbiotic star consist … More ing of a white dwarf and a mass-losing red giant. Both the systems contribute to main parts of the SN la birth rate.In the second year of my research, we have showed that the borders of such two regions of the WD+MS systems (SSS channel) and the WD+RG systems (symbiotic channel) correspond to the recurrent novae. These recurrent novae lie on the boarder of their parameter region that can produce an SN Ia. Foi example, we have estimated, from the light curve fitting, that the white dwarf mass of U Sco, one of the recurrent nova, is as large as 1.37 solar masses, just before the SN Ia explosion.In the third year of my research, we have also estimated the while dwaif masses for other recurrent novae, for example, symbiotic type recurrent novae, RS Oph, T CrB, and so on. The estimated masses are also very close to the Chandrasekhar mass limit. It is concluded that the member of the recurrent nova class are an immediate progenitor of Type la supernovae.In the final year of my research, we have theoretically identified the system just in the accretion wind evolution. The supersoft X-ray source in the Large Magellanic Clouds (LMC), RX J0513.9-6951, shows a prominent transition between optical high and optical low stales. Soft X-rays were observed only in the optical low stale. We have modeled the on/off of soft X-rays as well as the optical high/low states based on our optically thick wind mass loss model of mass-accreting while dwarfs. We have already predicted such systems in the accretion wind evolutions. This strongly supports our evokutionary model to Type Ia supernovae. Less