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arXiv 1807.07582astro-ph.SRastro-ph.GA
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半人马座欧米茄低红巨星分支星的锂丰度

Lithium abundance in lower red giant branch stars of Omega Centauri

A. Mucciarelli, M. Salaris, L. Monaco, P. Bonifacio, X. Fu, S. Villanova

备注：
Accepted for publication in A&A, 10 pages, 9 figures, 2 tables
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摘要：

我们目前的锂，钠，铝和铁丰度的199个较低的红巨星分支恒星系统欧米茄半人马座成员，使用高分辨率光谱获得火焰在甚大望远镜。A（Li）分布在A（Li）~ 1 dex处达到峰值，具有朝向较低值的突出尾部。分布的峰值与球状星团中较低的红巨星分支星和银河场星中测得的锂丰度一致。当金属丰度低于[Fe/H]-1.3dex时，A（Li）~ 1dex的恒星出现，当金属丰度高于[Fe/H] ~-1.3dex时，A（Li）~ 1dex的恒星消失。另一方面，在所有的金属丰度中都发现了贫锂星。大多数贫金属恒星表现出明显的Li-Na关系，大约30%的样本A（Li）低于~ 0.8 dex，而在正常的球状星团中，这些恒星只占一小部分。[Fe/H] >-1.6dex的恒星大多贫Li富Na。在这些恒星中测得的锂耗尽没有观察到类似的金属丰度的球状星团，我们证明，它不是由拟议的氦增强和/或年轻的年龄。因此，这些恒星是由已经耗尽锂的气体形成的。最后，我们注意到，半人马座欧米茄包括所有的人口（锂正常/钠正常，锂正常/钠丰富和锂穷人/钠丰富的恒星）观察到，在较小程度上，在单金属GC。

英文摘要：

We present Li, Na, Al and Fe abundances of 199 lower red giant branch stars members of the stellar system Omega Centauri, using high-resolution spectra acquired with FLAMES at the Very Large Telescope. The A(Li) distribution is peaked at A(Li) ~ 1 dex with a prominent tail toward lower values. The peak of the distribution well agrees with the lithium abundances measured in lower red giant branch stars in globular clusters and Galactic field stars. Stars with A(Li) ~ 1 dex are found at metallicities lower than [Fe/H] ~ -1.3 dex but they disappear at higher metallicities. On the other hand, Li-poor stars are found at all the metallicities. The most metal-poor stars exhibit a clear Li-Na anticorrelation, with about 30% of the sample with A(Li) lower than ~ 0.8 dex, while in normal globular clusters these stars represent a small fraction. Most of the stars with [Fe/H] > -1.6 dex are Li-poor and Na-rich. The Li depletion measured in these stars is not observed in globular clusters with similar metallicities and we demonstrate that it is not caused by the proposed helium enhancements and/or young ages. Hence, these stars formed from a gas already depleted in lithium. Finally, we note that Omega Centauri includes all the populations (Li-normal/Na-normal, Li-normal/Na-rich and Li-poor/Na-rich stars) observed, to a lesser extent, in mono-metallic GCs.

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