Oxygen and light-element synthesis by neutron-capture reactions in metal-free and extremely metal-poor AGB stars
Oxygen and light-element synthesis by neutron-capture reactions in metal-free and extremely metal-poor AGB stars
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DOI：
10.1093/pasj/61.5.909
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发表时间：
2009-06
影响因子：
2.3
通讯作者：
Takanori Nishimura;M. Aikawa;T. Suda;M. Fujimoto
中科院分区：
文献类型：
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作者：
Takanori Nishimura;M. Aikawa;T. Suda;M. Fujimoto
不含金属（第三星族：Pop. III）和中低质量的极贫金属（EMP）恒星在早期TP-AGB阶段经历了氢与氦对流的混合，与富金属恒星不同。本文用H到S的核网络研究了氦对流区中以混合质子生成的~（13）C为中子源的核合成。在缺乏或缺乏原始金属的情况下，中子再循环反应，12 C（n，γ）13 C（α，n）16 O和16 O（n，γ）17 O（α，n）20 Ne促进了O和轻元素的合成，包括它们的富中子同位素和奇数原子序数元素。基于这些结果，我们证明了三个最缺铁的富碳恒星中观察到的C到Al的特殊丰度模式可以在Pop. III，AGB恒星的三个不同质量范围内的核合成中重现。我们认为，这三颗恒星出生的低质量成员的Pop. III双星，后来受到表面污染的质量转移的双星系统。AGB核合成与氢混合解释了大多数碳增强EMP（CEMP）星（包括所有具有s-过程元素的CEMP-s星）的C、O、Na、Mg和Al丰度。此外，目前的结果被用来挑选出核合成签名的早期世代的恒星以外的AGB星。© 2009年。日本天文学会。
The metal-free (Population III: Pop. III) and extremely metal-poor (EMP) stars of low-and intermediate-masses experience mixing of hydrogen into the helium convection during the early TP-AGB phase, differently from the metal-rich stars. We have studied nucleosynthesis in the helium convective zone with 13C formed from mixed protons as a neutron source by using a nuclear network from H through S. In the absence or scarcity of pristine metals, neutron-recycling reactions, l2C (n, γ) 13C (α, n) 16O and also 16O (n, γ) 17O (α, n) 20Ne promote the synthesis of O and light elements, including their neutron-rich isotopes and the odd atomic number elements. Based on the results, we demonstrate that the peculiar abundance patterns of C through Al observed for the three most irondeficient, carbon-rich stars can be reproduced in terms of nucleosynthesis in Pop. III, AGB stars in three different mass ranges. We argue that these three stars were born as low-mass members of Pop. III binaries, and later were subjected to surface pollution by mass transfer in the binary systems. It is also shown that AGB nucleosynthesis with hydrogen mixing explains the abundances of C, O, Na, Mg, and Al observed for most of carbon-enhanced EMP (CEMP) stars, including all CEMP-s stars with s-process elements. In addition, the present results are used to single out nucleosynthetic signatures of the early generations of stars other than AGB stars. © 2009. Astronomical Society of Japan.