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Enormous Li-enhancement preceding red giant phases in low-mass stars in the Milky Way halo

机译:中国低质量恒星中红巨星相位前的巨大李增强   银河系的光环

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摘要

Li abundances in the bulk of low-mass metal-poor stars are well reproduced bystellar evolution models adopting a constant initial abundance. However, asmall number of stars have exceptionally high Li abundances, for which noconvincing models have been established. We report on the discovery of 12 verymetal-poor stars that have large excesses of Li, including an object havingmore than 100 times higher Li abundance than the values found in usual objects,which is the the largest excess in metal-poor stars known to date. The sampleis distributed over a wide range of evolutionary stages, including fiveunevolved stars, showing no abundance anomaly in other elements. The resultsindicate the existence of an efficient process to enrich Li in a small fractionof low-mass stars at the main-sequence or subgiant phase. The wide distributionof Li-rich stars along the red giant branch could be explained by dilution ofsurface Li by mixing that occurs when the stars evolve into red giants. Ourstudy narrows down the problem to be solved to understand the origins ofLi-excess found in low-mass stars, suggesting the presence of unknown processthat affects the surface abundances preceding red giant phases.
机译:通过采用恒定初始丰度的恒星演化模型可以很好地再现大量低质量金属贫乏恒星中的Li丰度。但是,少数恒星具有极高的Li丰度,因此尚未建立令人信服的模型。我们报告发现了12个极富锂的极贫金属恒星,其中一个天体的Li丰度比普通天体中发现的值高100倍以上,这是迄今为止已知的最大贫金属恒星中最大的一个。样品分布在广泛的演化阶段,包括五颗未演化的恒星,显示其他元素没有丰度异常。结果表明,存在一种有效的过程,可以在主序或次亚相阶段富集一小部分低质量恒星中的锂。富含锂的恒星沿着红色巨星分支的广泛分布可以通过表面恒星Li的稀释来解释,这种混合是在恒星演化为红色巨星时发生的。我们的研究缩小了要解决的问题,以了解低质量恒星中发现的Li过量的起源,这表明存在未知的过程会影响红色巨星相之前的表面丰度。

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