Progenitors Of Type Ia Supernovae

This doctorial thesis is on the progenitors of type Ia supernovae (SNe Ia). In the thesis, I reviewed the study of SNe Ia, especially about the progenitor models and explosion models of SNe Ia. Among all the progenitor models, the most widely accepted one is the single degenerate Chandrasekhar model, in which a carbon-oxygen white dwatf (CO WD) accretes hydrogen-rich material from its companions until its mass reaches a mass～1.378M_? (close to Chandrasekhar mass), and then explodes as a SN Ia. The companion is probably a main sequence star or a slightly evolved star (WD+MS). In the theoretical framework of optically thick wind suggested by Hachisu et al. (1996), we studied the propeties of WD + MS channel comprehensively and systematically, including the parameter space of progenitors for SNe Ia, the evolution of birth rate of SNe Ia with time, the properties of the companion before and after SNe Ia explosion, and the impact between explosion ejecta and the companion. We found that:(1) The parameter space of WD + MS systems for SNe Ia evolves with metallicity.(2) The delayed time of SNe Ia from WD + MS channel is about 1 Gyr. The explosion time of SNe Ia becomes earlier for a high metallicity. The birth rate and the mean luminosity of SNe Ia increase with metallicity.(3) The Galactic birth rate of SNe Ia from WD+MS channel is around (0.7-1.0)×10^-3yr^-1, which is smaller but comparable to that inferred from observations.(4) The properties of the companions after SNe Ia explosion from WD + MS channel, including mass, radius, surface gravity and space velocity, are well consistent with those of Tycho G.(5) Based on the numerical simulation of Marietta et al. (2000) and Kasen et al. (2004), we studied the the percentage of SNe Ia with polarized spectrum and found that at least 75% of all SNe Ia can be detected by spectropolarimetric observations.(6) We can reproduce the distribution of color excess of SNe Ia at maximum light.(7) When one studies the interaction between supernova explosion ejecta and companion, the initial orbital period and the initial mass of companion in a WD + MS system as well as the evolutionary phase of companion when mass transfer begins, are very important.When one studies the progenitor models of SNe Ia, the dependence of the mass of CO WD on metallicity (i.e. the dependence of initial-final mass relationship on metallicity) is also very important. We also studied the dependence of initial-final mass relationship on metallicity and found that there is an obvious dependence of initial-final mass relationship on metallicity and the dependence is not monotone. When Z =0.04, the final mass of the WD for a given initial mass is at minimum. For higher or lower Z, the mass of WD is higher. For Z≥0.02, helium white dwarfs are formed from stars with initial mass-less than 1.0M_?. This result means that there should be many helium white dwarfs in metal-rich old clusters, which is supported by the observation of NGC6791.