THE ABUNDANCES OF NEUTRON-CAPTURE SPECIES IN THE VERY METAL-POOR GLOBULAR CLUSTER M15: A UNIFORM ANALYSIS OF RED GIANT BRANCH AND RED HORIZONTAL BRANCH STARS
THE ABUNDANCES OF NEUTRON-CAPTURE SPECIES IN THE VERY METAL-POOR GLOBULAR CLUSTER M15: A UNIFORM ANALYSIS OF RED GIANT BRANCH AND RED HORIZONTAL BRANCH STARS
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DOI：
10.1088/0004-6256/141/6/175
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发表时间：
2011-03
期刊：
影响因子：
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通讯作者：
J. Sobeck;R. P. Kraft;C. Sneden;G. Preston;J. Cowan;Graeme H. Smith;I. Thompson;S. Shectman;G. Burley
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文献类型：
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作者：
J. Sobeck;R. P. Kraft;C. Sneden;G. Preston;J. Cowan;Graeme H. Smith;I. Thompson;S. Shectman;G. Burley
球状星团M15的独特之处在于它显示了恒星与星星之间中子捕获元素的变化。之前已经对M15红巨星分支（RGB）和红色水平分支（RHB）恒星进行了全面的丰度调查。没有人试图对这些恒星进行单一的、自洽的分析，这些恒星的大气参数范围很广。在目前的努力中，一个新的比较丰度推导提出了三个RGB和六个RHB成员的集群。分析采用了更新版本的线传输代码MOOG，现在适当地对待相干，各向同性散射。M15 RGB星和RHB星的金属丰度值存在明显差异，铁丰度的绝对差异为Δ（RHB − RGB）<$0.1 dex。轻中子俘获元素（Sr，Y，Zr）的反相关行为分别用s-和r-过程的标准标记Ba和Eu清楚地证明。在RGB目标中未进行Pb的确定性检测。因此，对于M15星团，这表明s过程的主要成分对太阳系物质中通常由该过程主导的元素的贡献可以忽略不计。此外，对于M15样品，确认了大的Eu丰度分布，这与相同金属丰度的晕场相当。这些丰度的结果被认为是在讨论的化学不均匀性和核合成的历史M15。
The globular cluster M15 is unique in its display of star-to-star variations in the neutron-capture elements. Comprehensive abundance surveys have been previously conducted for handfuls of M15 red giant branch (RGB) and red horizontal branch (RHB) stars. No attempt has been made to perform a single, self-consistent analysis of these stars, which exhibit a wide range in atmospheric parameters. In the current effort, a new comparative abundance derivation is presented for three RGB and six RHB members of the cluster. The analysis employs an updated version of the line transfer code MOOG, which now appropriately treats coherent, isotropic scattering. The apparent discrepancy in the previously reported values for the metallicity of M15 RGB and RHB stars is addressed and a resolute disparity of Δ(RHB − RGB) ≈ 0.1 dex in the iron abundance was found. The anti-correlative behavior of the light neutron-capture elements (Sr, Y, Zr) is clearly demonstrated with both Ba and Eu, standard markers of the s- and r-process, respectively. No conclusive detection of Pb was made in the RGB targets. Consequently for the M15 cluster, this suggests that the main component of the s-process has made a negligible contribution to those elements normally dominated by this process in solar system material. Additionally for the M15 sample, a large Eu abundance spread is confirmed, which is comparable to that of the halo field at the same metallicity. These abundance results are considered in the discussion of the chemical inhomogeneity and nucleosynthetic history of M15.