arXiv astro-ph/02012842002-01-17astro-ph

原始恒星的结构、演化与核合成

Structure, Evolution and Nucleosynthesis of Primordial Stars

Lionel Siess, Mario Livio, John Lattanzio

备注：: 26 pages, 13 figures, 6 tables, uses aastex. Accepted for publication in ApJ. Full postscript version available at http://www-astro.ulb.ac.be/~siess
DOI：: 10.1086/339733

摘要：

（简略版）第III星族星（Z=0）的演化是从主序前阶段到中等质量恒星的AGB阶段和更大质量恒星的C点火阶段。我们发现，由于混合事件（碳注入）在AGB阶段开始时的发展，1，1.5，2，3，4和5 Mo模型的碳丰度显着增加的信封。这一过程使低质量和中等质量的恒星能够达到“标准”的热脉冲AGB阶段。在7 Mo模型中，第二次挖掘后的CNO包层丰度是如此之大，以至于恒星没有经历碳注入事件，并遵循更标准的热脉冲AGB演化。我们的计算还表明，由于对流包层底部有一个小的过冲，第三次挖掘已经在M >~1.5 Mo的恒星中进行了几次脉冲，并且在我们的模拟结束时，热底部燃烧在质量大于~ 2 Mo的恒星中被激活。这种演化行为表明，原始的低和中等恒星可能是主要的12 C，14 N的产生的重要贡献者，并可能在一定程度上有助于早期宇宙中Mg和Al以及可能的s元素（尽管缺乏铁种子）的产生。

英文摘要：

(abridge version) The evolution of population III stars (Z=0) is followed from the pre-main sequence phase up to the AGB phase for intermediate-mass stars and up to C ignition in more massive stars...We find that, thanks to the development of mixing episodes (carbon injections) at the beginning of the AGB phase, the carbon abundance of the 1, 1.5, 2, 3, 4 and 5Mo models is significantly increased in the envelope. This process then allows low- and intermediate-mass stars to achieve a ``standard'' thermally pulsing AGB phase... In the 7Mo model, the CNO envelope abundance following the second dredge-up is so large that the star does not experience the carbon injection episode and follows a more standard thermally pulsing AGB evolution. Our computations also indicate that, thanks to a small overshooting at the base of the convective envelope, the third dredge-up is already operating in stars with M >~1.5 Mo after a few pulses, and that by the end of our modeling, hot bottom burning is activated in stars more massive than ~ 2Mo. This evolutionary behavior suggests that primordial low- and intermediate stars could have been significant contributors to the production of primary 12C, 14N, and may have contributed to some extent to the production of Mg and Al and possibly s-elements (despite the lack of iron seeds) in the early universe.

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英文摘要：

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