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  • 标题:Pre-supernova mixing in CEMP-no source stars
  • 本地全文:下载
  • 作者:Arthur Choplin ; Arthur Choplin ; Sylvia Ekström
  • 期刊名称:Astronomy & Astrophysics
  • 印刷版ISSN:0004-6361
  • 电子版ISSN:1432-0746
  • 出版年度:2017
  • 卷号:605
  • 页码:1-17
  • DOI:10.1051/0004-6361/201630182
  • 语种:English
  • 出版社:EDP Sciences
  • 摘要:Context. CEMP-no stars are long-lived low-mass stars with a very low iron content, overabundances of carbon and no or minor signs for the presence of s- or r-elements. Although their origin is still a matter of debate, they are often considered as being made of a material ejected by a previous stellar generation (source stars). Aims. We place constraints on the source stars from the observed abundance data of CEMP-no stars. Methods. We computed source star models of 20, 32, and 60 M⊙ at Z = 10-5 with and without fast rotation. For each model we also computed a case with a late mixing event occurring between the hydrogen and helium-burning shell ~200 yr before the end of the evolution. This creates a partially CNO-processed zone in the source star. We use the 12C/13C and C/N ratios observed on CEMP-no stars to put constraints on the possible source stars (mass, late mixing or not). Then, we inspect more closely the abundance data of six CEMP-no stars and select their preferred source star(s). Results. Four out of the six CEMP-no stars studied cannot be explained without the late mixing process in the source star. Two of them show nucleosynthetic signatures of a progressive mixing (due e.g. to rotation) in the source star. We also show that a 20 M⊙ source star is preferred compared to one of 60 M⊙ and that likely only the outer layers of the source stars were expelled to reproduce the observed 12C/13C. Conclusions. The results suggest that (1) a late mixing process could operate in some source stars; (2) a progressive mixing, possibly achieved by fast rotation, is at work in several source stars; (3) ~20 M⊙ source stars are preferred compared to ~60 M⊙ ones; and (4) the source star might have preferentially experienced a low energetic supernova with large fallback.
  • 关键词:enstars: abundancesstars: massivestars: chemically peculiarnuclear reactions, nucleosynthesis, abundancesstars: interiors
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