极端外晕球状星团NGC 2419的奇异化学物质表
The Bizarre Chemical Inventory of NGC 2419, An Extreme Outer Halo Globular Cluster
摘要：
我们提出了新的凯克/HIRES观测六红巨星的球状星团NGC 2419。虽然这个星系团是银河系中最遥远、最明亮的星系团之一，但直到最近它才被认为是化学上普通的。我们之前的工作表明，近红外Ca II三线态强度的变化比化学均匀的星团所预期的要大，并且至少有一颗恒星具有不寻常的Mg和K丰度。在这里，我们确认，NGC 2419窝藏人口的恒星，包括约三分之一的质量，这是在镁耗尽的8倍，并增强了K的6倍，相对于镁正常人口。虽然大多数，镁正常人口似乎有一个普通的，内晕球状星团的化学丰度模式无法区分，镁穷人人口表现出分散的几个元素。K和Sc的丰度与Mg呈强反相关，而其他一些元素（Si和Ca等）与Mg呈弱反相关。这些丰度模式表明，NGC 2419的不同种群除了采集AGB喷出物外，还采集了不同超新星的喷出物。除Sc外，Fe峰元素的丰度没有星间变化。我们没有发现核合成源，令人满意地解释了所有的丰度变化，在这个集群。因为NGC 2419看起来不像其他球状星团，我们重申我们之前的建议，它根本不是一个球状星团，而是一个吸积矮星系的核心。
英文摘要：
We present new Keck/HIRES observations of six red giants in the globular cluster NGC 2419. Although the cluster is among the most distant and most luminous in the Milky Way, it was considered chemically ordinary until very recently. Our previous work showed that the near-infrared Ca II triplet line strength varied more than expected for a chemically homogeneous cluster, and that at least one star had unusual abundances of Mg and K. Here, we confirm that NGC 2419 harbors a population of stars, comprising about one third of its mass, that is depleted in Mg by a factor of 8 and enhanced in K by a factor of 6 with respect to the Mg-normal population. Although the majority, Mg-normal population appears to have a chemical abundance pattern indistinguishable from ordinary, inner halo globular clusters, the Mg-poor population exhibits dispersions of several elements. The abundances of K and Sc are strongly anti-correlated with Mg, and some other elements (Si and Ca among others) are weakly anti-correlated with Mg. These abundance patterns suggest that the different populations of NGC 2419 sample the ejecta of diverse supernovae in addition to AGB ejecta. However, the abundances of Fe-peak elements except Sc show no star-to-star variation. We find no nucleosynthetic source that satisfactorily explains all of the abundance variations in this cluster. Because NGC 2419 appears like no other globular cluster, we reiterate our previous suggestion that it is not a globular cluster at all, but rather the core of an accreted dwarf galaxy.
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