SPECTROSCOPIC ANALYSIS OF METAL-POOR STARS FROM LAMOST: EARLY RESULTS
SPECTROSCOPIC ANALYSIS OF METAL-POOR STARS FROM LAMOST: EARLY RESULTS
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DOI：
10.1088/0004-637x/798/2/110
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发表时间：
2015-01
期刊：
影响因子：
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通讯作者：
Haining Li;Gang Zhao;N. Christlieb;Liang-Yao Wang;Wei Wang;Yong Zhang;Yong-Hui Hou;Hailong Yuan-Hailong
中科院分区：
文献类型：
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作者：
Haining Li;Gang Zhao;N. Christlieb;Liang-Yao Wang;Wei Wang;Yong Zhang;Yong-Hui Hou;Hailong Yuan-Hailong
我们报告了利用大天区面积多目标光纤光谱天文望远镜（LAMOST）寻找贫金属恒星的试点项目的早期结果，以及利用麦哲伦二号望远镜上的迈克光谱仪进行的后续高分辨率观测结果。我们对8个铁丰度[Fe/H] < -2.0的天体进行了详细的丰度分析，其中包括5颗极贫金属（EMP；[Fe/H] < -3.0）恒星，有2颗的[Fe/H] < -3.5。在这些天体中，有3颗是新发现的极贫金属恒星，其中1颗首次通过高分辨率光谱观测得到确认。3颗项目恒星被视为碳增丰贫金属（CEMP）恒星，其中2颗的中子俘获元素没有增丰，因此可能属于CEMP - no星族；其中1个天体的氮也有显著增丰，因此是一颗潜在的碳氮增丰贫金属恒星。样本恒星的[X/Fe]比值通常与文献中报道的相同[Fe/H]范围内的其他贫金属恒星的比值一致。我们还将单个项目恒星的丰度模式与贫金属恒星的平均丰度模式进行了比较，发现只有1个化学性质特殊的天体，其至少两种元素（除C和N外）的丰度偏差大于0.5 dex。[Sr/Ba]与[Ba/H]的分布表明，除了单一的r - 过程外，还需要一种额外的核合成机制。2颗锶和钡丰度极低的项目恒星支持了在银河系化学演化早期主r - 过程和弱r - 过程可能都起作用的观点。[C/N]的分布表明，存在两组混合程度不同的碳正常巨星。然而，基于现有数据很难解释氮增丰未演化恒星的[C/N]观测行为。
We report on early results from a pilot program searching for metal-poor stars with LAMOST and follow-up high-resolution observation acquired with the MIKE spectrograph attached to the Magellan II telescope. We performed detailed abundance analysis for eight objects with iron abundances [Fe/H] < -2.0, including five extremely metal-poor (EMP; [Fe/H] < -3.0) stars with two having [Fe/H] < -3.5. Among these objects, three are newly discovered EMP stars, one of which is confirmed for the first time with high-resolution spectral observations. Three program stars are regarded as carbon-enhanced metal-poor (CEMP) stars, including two stars with no enhancement in their neutron-capture elements, which thus possibly belong to the class of CEMP-no stars; one of these objects also exhibits significant enhancement in nitrogen, and is thus a potential carbon and nitrogen-enhanced metal-poor star. The [X/Fe] ratios of the sample stars generally agree with those reported in the literature for other metal-poor stars in the same [Fe/H] range. We also compared the abundance patterns of individual program stars with the average abundance pattern of metal-poor stars and find only one chemically peculiar object with abundances of at least two elements (other than C and N) showing deviations larger than 0.5 dex. The distribution of [Sr/Ba] versus [Ba/H] agrees that an additional nucleosynthesis mechanism is needed aside from a single r-process. Two program stars with extremely low abundances of Sr and Ba support the prospect that both main and weak r-processes may have operated during the early phase of Galactic chemical evolution. The distribution of [C/N] shows that there are two groups of carbon-normal giants with different degrees of mixing. However, it is difficult to explain the observed behavior of the [C/N] of the nitrogen-enhanced unevolved stars based on current data.