WIYN Open Cluster Study. LXXXI. Caught in the Act? The Peculiar Red Giant NGC 2243-W2135
WIYN Open Cluster Study. LXXXI. Caught in the Act? The Peculiar Red Giant NGC 2243-W2135
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DOI：
10.3847/1538-3881/ab9ca2
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发表时间：
2020-06
期刊：
影响因子：
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通讯作者：
B. Anthony-Twarog;C. Deliyannis;B. Twarog
中科院分区：
文献类型：
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作者：
B. Anthony-Twarog;C. Deliyannis;B. Twarog
在古老的、缺乏金属的疏散星团 NGC 2243 中，已经获得并分析了 Li 6708 Å 区域中巨星通过关闭恒星的高色散光谱。当与其他巡天的高色散数据相结合时，发现该星团包含一颗处于红色团簇光度水平的独特恒星。这颗巨星是光度最红的恒星，在天的时间尺度上表现出最小 0.1 星等的变化，是单线径向速度变星，并且具有 35 至 40 km s−1 之间。与大多数红巨星团成员形成鲜明对比的是，这颗恒星具有可检测到的锂丰度，可能与迄今为止观察到的其他巨星一样高或更高，同时处于或略低于通常用于富锂巨星的边界。观察到的异常现象可能是该巨人实现其异常锂丰度的潜在过程的指标，在当前有限的限制内，最近的传质事件是最有可能发生的。
High-dispersion spectra for giants through turnoff stars in the Li 6708 Å region have been obtained and analyzed in the old, metal-deficient open cluster, NGC 2243. When combined with high-dispersion data from other surveys, the cluster is found to contain a uniquely peculiar star at the luminosity level of the red clump. The giant is the reddest star at its luminosity, exhibits variability at a minimum 0.1 mag level on a timescale of days, is a single-lined, radial-velocity variable, and has between 35 and 40 km s−1. In sharp contrast with the majority of the red giant cluster members, the star has a detectable Li abundance, potentially as high or higher than other giants observed to date while at or just below the boundary normally adopted for Li-rich giants. The observed anomalies may be indicators of the underlying process by which the giant has achieved its unusual Li abundance, with a recent mass transfer episode being the most probable within the currently limited constraints.