The first stars: CEMP--no stars and signatures of spinstars
The first stars: CEMP--no stars and signatures of spinstars
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DOI：
10.1051/0004-6361/201424153
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发表时间：
2014-12
期刊：
影响因子：
--
通讯作者：
A. Maeder;G. Meynet;C. Chiappini
中科院分区：
文献类型：
--
作者：
A. Maeder;G. Meynet;C. Chiappini
（节略）CEMP-没有恒星是“碳增强-金属贫乏”的恒星，原则上没有证据表明中子捕获的s和r元素。我们试图了解它们特有的CNO、Ne-Na和Mg-Al丰度的起源和核合成位点。我们比较所观察到的丰度的核合成预测的AGB模型和模型的旋转大质量恒星内部混合和质量损失。我们还分析了$\alpha$-和CNO-元素的不同行为，以及参与Ne-Na和Mg-Al循环的元素的丰度。我们发现，CEMP-没有明星表现出的产品，他-燃烧已经通过部分混合和处理的CNO循环，产生低$^{12}$C/$^{13}$C和各种各样的[C/N]和[O/N]的比例。从$^{12}$C/$^{13}$C与[C/N]图中，我们得出结论，无论是AGB星的产额（是否为双星）还是经典超新星的产额都无法完全解释CEMP中观察到的CNO丰度-无星。一旦考虑到快速旋转的大质量恒星的恒星风的化学贡献，就会获得更好的一致性，其中发生部分混合，导致喷射出不同数量的CNO。CEMP--没有恒星的[C/Fe]、[N/Fe]、[O/Fe]、[Na/Fe]、[Mg/Fe]、[Al/Fe]和[Sr/Fe]比值变化很大。我们表明，来回，部分混合之间的He-和H-区域可能占这种多样性。一些s-元素，主要是第一个峰，甚至可能是由这些过程中产生的CEMP的一小部分-没有恒星。我们提出了一个分类方案的CEMP-没有和低-s星，根据这些连续的来回混合运动所产生的组成的变化。
(Abridged) The CEMP--no stars are "carbon-enhanced-metal-poor" stars that in principle show no evidence of s-- and r--elements from neutron captures. We try to understand the origin and nucleosynthetic site of their peculiar CNO, Ne--Na, and Mg--Al abundances. We compare the observed abundances to the nucleosynthetic predictions of AGB models and of models of rotating massive stars with internal mixing and mass loss. We also analyze the different behaviors of $\alpha$-- and CNO--elements, as well the abundances of elements involved in the Ne--Na and Mg--Al cycles. We show that CEMP-no stars exhibit products of He--burning that have gone through partial mixing and processing by the CNO cycle, producing low $^{12}$C/$^{13}$C and a broad variety of [C/N] and [O/N] ratios. From a $^{12}$C/$^{13}$C vs. [C/N] diagram, we conclude that neither the yields of AGB stars (in binaries or not) nor the yields of classic supernovae can fully account for the observed CNO abundances in CEMP-no stars. Better agreement is obtained once the chemical contribution by stellar winds of fast-rotating massive stars is taken into account, where partial mixing takes place, leading to various amounts of CNO being ejected. CEMP--no stars present a wide variety in the [C/Fe], [N/Fe], [O/Fe], [Na/Fe], [Mg/Fe], [Al/Fe], and [Sr/Fe] ratios. We show that back-and-forth, partial mixing between the He-- and H--regions may account for this variety. Some s--elements, mainly of the first peak, may even be produced by these processes in a small fraction of the CEMP--no stars. We propose a classification scheme for the CEMP--no and low--s stars, based on the changes in composition produced by these successive back-and-forth mixing motions.