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arXiv 1402.4144astro-ph.SRastro-ph.GA
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第一批恒星的中子俘获核合成

Neutron-Capture Nucleosynthesis in the First Stars

Ian U. Roederer, George W. Preston, Ian B. Thompson, Stephen A. Shectman, Chris Sneden

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Accepted for publication in the Astrophysical Journal (36 pages, 26 figures)
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摘要：

最近的研究表明，贫金属恒星的碳含量增加，但含有低水平的中子捕获元素，可能是第一代恒星核合成产物的第一批。我们已经观察到16颗恒星的增强碳或氮使用的MIKE光谱仪麦哲伦望远镜在拉斯坎帕纳斯天文台和塔尔光谱仪史密斯望远镜在麦当劳天文台。我们目前的径向速度，恒星参数，和详细的丰度模式，这些恒星。锶、钇、锆、钡、铕、镱和其他重元素被检测到。在四颗恒星中，这些重元素似乎起源于某种形式的r-过程核合成。在一颗恒星中，部分s过程起源是可能的。其余样品中重元素的来源无法明确确定。比铁族重的元素的存在提供了进一步的证据，证明零金属丰度、快速旋转的大质量恒星和对不稳定性超新星并没有为我们样本中的恒星形成的区域贡献大量的中子捕获元素。如果碳或氮增强的贫金属恒星具有低水平的中子捕获元素，则这些重元素的存在表明，在某些最初的恒星中至少有一种形式的中子捕获反应。

英文摘要：

Recent studies suggest that metal-poor stars enhanced in carbon but containing low levels of neutron-capture elements may have been among the first to incorporate the nucleosynthesis products of the first generation of stars. We have observed 16 stars with enhanced carbon or nitrogen using the MIKE Spectrograph on the Magellan Telescopes at Las Campanas Observatory and the Tull Spectrograph on the Smith Telescope at McDonald Observatory. We present radial velocities, stellar parameters, and detailed abundance patterns for these stars. Strontium, yttrium, zirconium, barium, europium, ytterbium, and other heavy elements are detected. In four stars, these heavy elements appear to have originated in some form of r-process nucleosynthesis. In one star, a partial s-process origin is possible. The origin of the heavy elements in the rest of the sample cannot be determined unambiguously. The presence of elements heavier than the iron group offers further evidence that zero-metallicity rapidly-rotating massive stars and pair instability supernovae did not contribute substantial amounts of neutron-capture elements to the regions where the stars in our sample formed. If the carbon- or nitrogen-enhanced metal-poor stars with low levels of neutron-capture elements were enriched by products of zero-metallicity supernovae only, then the presence of these heavy elements indicates that at least one form of neutron-capture reaction operated in some of the first stars.

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