Helium-star evolutionary channel to super-Chandrasekhar mass type Ia supernovae

¹ Department of PhysicsShangqiu Normal University, Shangqiu 476000, PR China
e-mail: chenwc@nju.edu.cn
² School of Physics and State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing 100871, PR China
³ Key Laboratory of Modern Astronomy and Astrophysics (Nanjing University), Ministry of Education, Nanjing 210093, PR China
⁴ National Astronomical Observatories/Yunnan Observatory, the Chinese Academy of Sciences, Kunming 650011, PR China
⁵ Key Laboratory for the Structure and Evolution of Celestial Objects, the Chinese Academy of Sciences, Kunming 650011, PR China

Received: 2 February 2010
Accepted: 27 July 2010

Abstract

The recent discovery of several overluminous type Ia supernovae (SNe Ia) indicates that the explosive masses of white dwarfs may significantly exceed the canonical Chandrasekhar-mass limit. Rapid differential rotation may support these massive white dwarfs (WDs). Based on the single-degenerate scenario and assuming that the WDs would differentially rotate when the accretion rate Ṁ > 3 × 10^-7   M_⊙   yr^-1, we performed the numerical calculations for  ~ 1000 binary systems consisting of a He star and a CO WD with Eggleton’s stellar evolution code. We present the initial parameters in the orbital period  −  helium star-mass plane (for WD masses of 1.0   M_⊙ and 1.2   M_⊙, respectively), which lead to super-Chandrasekhar mass SNe Ia. Our results indicate that for an initially massive WD of 1.2   M_⊙, a large number of SNe Ia may result from super-Chandrasekhar mass WDs. The highest mass of the WD at the moment of the SNe Ia explosion is 1.81 M_⊙, but very massive ( > 1.85   M_⊙) WDs cannot be formed. However, when the initial mass of WDs is 1.0   M_⊙, the explosive masses of SNe Ia are nearly uniform, which is consistent with the rareness of super-Chandrasekhar mass SNe Ia in observations.