论文标题
与碳氧和氦白矮人合并的超质量氧气白色矮人形成
Formation of ultra-massive carbon-oxygen white dwarfs from the merger of carbon-oxygen and helium white dwarf pairs
论文作者
论文摘要
超过1.05ms的质量的超质量白色矮人（UMWD）基本上被认为含有氧气（一个）核心。最近，Gaia数据揭示了Hertzsprung-Russell图（HRD）上UMWD的增强，这表明UMWD中可能存在额外的冷却延迟机制，例如结晶和元素沉积。进一步的研究表明，一部分UMWD应该经历相当长的冷却延迟，这意味着它们是碳氧（CO）WDS。但是，这些UMCOWD的形成机制仍在争论中。在这项工作中，我们调查了大规模WD与氦气WD（HE WDS）的合并是否可以演变为Umcowds。通过采用恒星进化代码MESA，我们构建了双WD合并残留物来调查其最终命运。我们发现，残留物的合并后演变与R CRB恒星相似。 He壳的氦气燃烧以从2.0*10^-6至5.0*10^-6 msun/yr的速率导致CO核心的质量生长。最终的CO WD质量受到合并后演化期间风质量的速率的影响，并且不能超过1.2msun。核心质量大于1.2msun的残留物将遇到表面碳点火，这可能最终以一个WD结束生命。当前的结果表明，至少有一部分会经历额外的较长冷却延迟的UMWD，可能是由于合并和WD的合并而导致的。
Ultra-massive white dwarfs (UMWDs) with masses larger than 1.05Msun are basically believed to harbour oxygen-neon (ONe) cores. Recently, Gaia data reveals an enhancement of UMWDs on Hertzsprung-Russell diagram (HRD), which indicates that extra cooling delay mechanism such as crystallization and elemental sedimentation may exist in the UMWDs. Further studies suggested that a portion of UMWDs should have experienced pretty long cooling delays, implying that they are carbon-oxygen (CO) WDs. However, the formation mechanism of these UMCOWDs is still under debate. In this work, we investigated whether the merges of massive CO WDs with helium WDs (He WDs) can evolve to UMCOWDs. By employing stellar evolution code MESA, we construct double WD merger remnants to investigate their final fates. We found that the post-merger evolution of the remnants are similar to R CrB stars. The helium burning of the He shell leads to the mass growing of the CO core at a rate from 2.0*10^-6 to 5.0*10^-6 Msun/yr . The final CO WD mass is influenced by the wind-mass-loss rate during the post-merger evolution, and cannot exceed about 1.2Msun. The remnants with core mass larger than 1.2Msun will experience surface carbon ignition, which may finally end their lives as ONe WDs. Current results implies that at least a portion of UMWDs which experience extra long cooling delay may stem from merging of CO WDs and He WDs.
