On the Progenitors of Super-chandrasekhar Mass Type Ia Supernovae

Type Ia supernovae (SNe Ia) can be used as the standard candlelight to determine the cosmological distances because they are thought to have a uniform fuel amount. Recent observations of several overluminous SNe Ia suggest that the white dwarf masses at supernova explosion may significantly exceed the canonical Chandrasekhar mass limit. These massive white dwarfs may be supported by rapid differential rotation. Based on single degenerate model and the assumption that the white dwarf would differentially rotate when the accretion rate Ṁ > 3 × 10M⊙yr, we have calculated the evolutions of close binaries consisting of a white dwarf and a normal companion. To include the effect of rotation, we introduce an effective mass Meff for white dwarfs. For the donor stars with two different metallicities Z = 0.02 and 0.001, we present the distribution of the initial donor star masses and the orbital periods of the progenitors of super-Chandrasekhar mass SNe Ia. The calculation results indicate that, for an initial massive white dwarf of 1.2M⊙, a considerable fraction of SNe Ia may result from super-Chandresekhar mass white dwarfs, but very massive (> 1.7M⊙) white dwarfs are difficult to form, and none of them could be found in old populations. However, super-Chandrasekhar mass SNe Ia are very rare when the initial mass of white dwarfs is 1.0M⊙. Additionally, SNe Ia in low metallicity environment are more likely to be homogeneous. Subject headings: binaries: close — stars: evolution — supernovae: general — white dwarfs