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>CA II TRIPLET SPECTROSCOPY OF SMALL MAGELLANIC CLOUD RED GIANTS. III. ABUNDANCES AND VELOCITIES FOR A SAMPLE OF 14 CLUSTERS
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CA II TRIPLET SPECTROSCOPY OF SMALL MAGELLANIC CLOUD RED GIANTS. III. ABUNDANCES AND VELOCITIES FOR A SAMPLE OF 14 CLUSTERS
We obtained spectra of red giants in 15 Small Magellanic Cloud (SMC) clusters in the region of the Ca ii lines with FORS2 on the Very Large Telescope. We determined the mean metallicity and radial velocity with mean errors of 0.05 dex and 2.6 km s?1, respectively, from a mean of 6.5 members per cluster. One cluster (B113) was too young for a reliable metallicity determination and was excluded from the sample. We combined the sample studied here with 15 clusters previously studied by us using the same technique, and with 7 clusters whose metallicities determined by other authors are on a scale similar to ours. This compilation of 36 clusters is the largest SMC cluster sample currently available with accurate and homogeneously determined metallicities. We found a high probability that the metallicity distribution is bimodal, with potential peaks at ?1.1 and ?0.8 dex. Our data show no strong evidence of a metallicity gradient in the SMC clusters, somewhat at odds with recent evidence from Ca ii triplet spectra of a large sample of field stars. This may be revealing possible differences in the chemical history of clusters and field stars. Our clusters show a significant dispersion of metallicities, whatever age is considered, which could be reflecting the lack of a unique age–metallicity relation in this galaxy. None of the chemical evolution models currently available in the literature satisfactorily represents the global chemical enrichment processes of SMC clusters.
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机译：我们用超大望远镜上的FORS2在Ca ii线区域中的15个小麦哲伦星云（SMC）群集中获得了红色巨人的光谱。我们从每簇6.5个成员的平均值中分别确定了平均金属度和径向速度，其平均误差分别为0.05 dex和2.6 km s？1。一个簇（B113）太小，无法进行可靠的金属度测定，因此被从样品中排除。我们将此处研究的样本与我们先前使用相同技术研究过的15个簇和其他作者确定的金属度与我们相似的7个簇结合在一起。这个由36个团簇组成的汇编是目前可用的最大的SMC团簇样本，具有准确且均质的金属含量。我们发现金属性分布呈双峰态的可能性很高，其潜在峰位于？1.1和？0.8 dex。我们的数据没有显示出SMC团簇中金属性梯度的有力证据，这与来自大量野外恒星的Ca ii三重态谱的最新证据有些矛盾。这可能揭示了团簇和田间恒星化学史的可能差异。无论考虑什么年龄，我们的星团都显示出金属的显着分散，这可能反映出该星系缺乏独特的年龄-金属性关系。目前文献中没有可用的化学演化模型令人满意地表示SMC簇的全球化学富集过程。
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