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arXiv 1708.07705astro-ph.SRastro-ph.GA
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NGC 6535：具有Na-O反相关的最低质量Milky Way球状星团？多种群背景下的集群质量和年龄

NGC 6535: the lowest mass Milky Way globular cluster with a Na-O anti-correlation? Cluster mass and age in the multiple population context

A. Bragaglia, E. Carretta, V. D'Orazi, A. Sollima, P. Donati, R. G. Gratton, S. Lucatello

备注：
In press on A&A. Table 2 available at CDS
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摘要：

要了解球状星团（GCs），我们需要了解它们的形成过程是如何产生轻元素丰度分布的。特别是，我们试图找出哪些恒星留下了GC的特殊化学特征。最好的方法之一是在大样本的GC中研究轻元素的反相关，这些GC是均匀分析的。作为我们的光谱调查的GC与火焰的一部分，我们在这里介绍了我们的研究结果，约30红巨星成员星的低质量，低金属量的银河系星团NGC 6535。我们测量了金属丰度（发现[Fe/H]=-1.95，rms=0.04 dex在我们的均匀尺度）和其他元素的集群，特别是，我们集中在这里的O和Na丰度。这些元素定义了经典GC的正常Na-O反相关性，使NGC 6535可能是确认存在多个种群的最低质量星系团。我们更新了银河系和河外GC的人口普查，其中关于多个种群的存在或不存在的声明可以优先基于高分辨率光谱学，或者测光和低分辨率光谱学，否则;我们还讨论了作为多个种群因素的星团质量和年龄的重要性。

英文摘要：

To understand globular clusters (GCs) we need to comprehend how their formation process was able to produce their abundance distribution of light elements. In particular, we seek to figure out which stars imprinted the peculiar chemical signature of GCs. One of the best ways is to study the light-element anti-correlations in a large sample of GCs that are analysed homogeneously. As part of our spectroscopic survey of GCs with FLAMES, we present here the results of our study of about 30 red giant member stars in the low-mass, low-metallicity Milky Way cluster NGC 6535. We measured the metallicity (finding [Fe/H]=-1.95, rms=0.04 dex in our homogeneous scale) and other elements of the cluster and, in particular, we concentrate here on O and Na abundances. These elements define the normal Na-O anti-correlation of classical GCs, making NGC 6535 perhaps the lowest mass cluster with a confirmed presence of multiple populations. We updated the census of Galactic and extragalactic GCs for which a statement on the presence or absence of multiple populations can be made on the basis of high-resolution spectroscopy preferentially, or photometry and low-resolution spectroscopy otherwise; we also discuss the importance of mass and age of the clusters as factors for multiple populations.

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