Hydrogen and helium shell burning during white dwarf accretion

• 来源期刊: 天文和天体物理学研究
• 年，卷（期）: 2018,（5）
• 页码范围: 159-166
• 页数: 8页
• 语种: 英文
• DOI: 10.1088/1674-4527/18/5/58

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.