High-resolution spectroscopic studies of ultra metal-poor stars found in the LAMOST survey
High-resolution spectroscopic studies of ultra metal-poor stars found in the LAMOST survey
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DOI：
10.1093/pasj/psv053
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发表时间：
2015-06
影响因子：
2.3
通讯作者：
Haining Li;W. Aoki;Gang Zhao;S. Honda;N. Christlieb;T. Suda
中科院分区：
文献类型：
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作者：
Haining Li;W. Aoki;Gang Zhao;S. Honda;N. Christlieb;T. Suda
我们报告了两颗[Fe/H]~-4.0的超贫金属（UMP）恒星的观测结果，其中包括一颗新发现。用LAMOST和Subaru寻找极贫金属（EMP）恒星的高效项目正在对这两颗恒星进行研究。利用Subaru/HDS获得了从Li到Eu的15种元素的高分辨率光谱，得到了详细的丰度或丰度上限。这两颗UMP恒星的丰度模式与低金属丰度恒星的“正常种群”一致。这两颗程序星都显示出碳增强，没有任何多余的重中子捕获元素，表明它们属于cep -无恒星的亚类，就像之前研究的大多数UMP恒星一样。这两颗cep -no - UMP恒星的Sr/Ba比值都在[Sr/Ba]~-0.4以上，表明碳过量的起源与s过程发生的AGB伴星的质量传递不相容。在新发现的UMP恒星LAMOST J125346.09+075343.1中测量了锂丰度，使其成为第二颗检测到锂的UMP关闭星。LAMOST J125346.09+075343.1的Li丰度略低于相似温度下金属含量较低的恒星，并提供了一个独特的[Fe/H]~-4.2的数据点，以支持在极低金属丰度下Li - spet高原的“熔解”。与其他两颗UMP和HMP（超贫金属，[Fe/H]<-5.0）关闭星的比较表明，CNO和Na等较轻元素的差异可能导致cmp -no恒星之间锂丰度的显着差异。
We report on the observations of two ultra metal-poor (UMP) stars with [Fe/H]~-4.0 including one new discovery. The two stars are studied in the on-going and quite efficient project to search for extremely metal-poor (EMP) stars with LAMOST and Subaru. Detailed abundances or upper limits of abundances have been derived for 15 elements from Li to Eu based on high-resolution spectra obtained with Subaru/HDS. The abundance patterns of both UMP stars are consistent with the "normal-population" among the low-metallicity stars. Both of the two program stars show carbon-enhancement without any excess of heavy neutron-capture elements, indicating that they belong to the subclass of CEMP-no stars, as is the case of most UMP stars previously studied. The [Sr/Ba] ratios of both CEMP-no UMP stars are above [Sr/Ba]~-0.4, suggesting the origin of the carbon-excess is not compatible with the mass transfer from an AGB companion where the s-process has operated. Lithium abundance is measured in the newly discovered UMP star LAMOST J125346.09+075343.1, making it the second UMP turnoff star with Li detection. The Li abundance of LAMOST J125346.09+075343.1 is slightly lower than the values obtained for less metal-poor stars with similar temperature, and provides a unique data point at [Fe/H]~-4.2 to support the "meltdown" of the Li Spite-plateau at extremely low metallicity. Comparison with the other two UMP and HMP (hyper metal-poor with [Fe/H]<-5.0) turnoff stars suggests that the difference in lighter elements such as CNO and Na might cause notable difference in lithium abundances among CEMP-no stars.