摘要
Type Ia supernovae（SNe Ia） are believed to be thermonuclear explosions of carbon oxygen（CO） white dwarfs（WDs） with masses close to the Chandrasekhar mass limit. How a CO WD accretes matter and grows in mass to this limit is not well understood, hindering our understanding of SN Ia explosions and the reliability of using SNe Ia as a cosmological distance indicator. In this work, we employed the stellar evolution code MESA to simulate the accretion process of hydrogen-rich material onto a 1.0 M⊙CO WD at a high rate（over the Eddington limit） of 4.3 × 10^-7 M⊙yr^-1. The simulation demonstrates the characteristics of the double shell burning on top of the WD, with a hydrogen shell burning on top of a helium burning shell. The results show that helium shell burning is not steady（i.e.it flashes）. Flashes from the helium shell are weaker than those in the case of accretion of helium-rich material onto a CO WD. The carbon to oxygen mass ratio resulting from the helium shell burning is higher than what was previously thought. Interestingly, the CO WD growing due to accretion has an outer part containing a small fraction of helium in addition to carbon and oxygen. The flashes become weaker and weaker as the accretion continues.
Type Ia supernovae（SNe Ia） are believed to be thermonuclear explosions of carbon oxygen（CO） white dwarfs（WDs） with masses close to the Chandrasekhar mass limit. How a CO WD accretes matter and grows in mass to this limit is not well understood, hindering our understanding of SN Ia explosions and the reliability of using SNe Ia as a cosmological distance indicator. In this work, we employed the stellar evolution code MESA to simulate the accretion process of hydrogen-rich material onto a 1.0 M⊙CO WD at a high rate（over the Eddington limit） of 4.3 × 10^-7 M⊙yr^-1. The simulation demonstrates the characteristics of the double shell burning on top of the WD, with a hydrogen shell burning on top of a helium burning shell. The results show that helium shell burning is not steady（i.e.it flashes）. Flashes from the helium shell are weaker than those in the case of accretion of helium-rich material onto a CO WD. The carbon to oxygen mass ratio resulting from the helium shell burning is higher than what was previously thought. Interestingly, the CO WD growing due to accretion has an outer part containing a small fraction of helium in addition to carbon and oxygen. The flashes become weaker and weaker as the accretion continues.
基金
partly supported by the National Natural Science Foundation of China(Grant Nos.11521303,11733008,11390374,11473063,11522327 and 11703081)
the Natural Science Foundation of Yunnan Province(Grant Nos.2013HA005,2017HC018 and 2015HB096)
CAS Light of West China Program
the Chinese Academy of Sciences(Grant No.KJZD-EW-M06-01)
