Light Element Abundances and Multiple Populations in M53
Light Element Abundances and Multiple Populations in M53
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DOI：
10.3847/1538-3881/abf04d
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发表时间：
2018-05
期刊：
影响因子：
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通讯作者：
J. Gerber;E. Friel;E. Vesperini
中科院分区：
文献类型：
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作者：
J. Gerber;E. Friel;E. Vesperini
我们介绍了对球状星团M53中的94颗红巨星的研究结果。我们使用低分辨率光谱分别在~ 3800和4300 Å测量CN和CH特征的强度。这些特征的强度被用来将恒星分为cn增强和cn正常种群，并测量所有94颗恒星的C和N丰度。我们发现红巨星分支恒星均匀地分布在两个已确定的星族之间，并且在渐近巨星分支上观察到cn增强恒星的存在。此外，我们根据它们的CN和CH波段特征的强度，以及它们的CH波段中p分支的存在，确定了5个CH星候选者。我们将我们的多种群识别与基于Na-O反相关和哈勃太空望远镜紫外测光法的伪色指数的识别进行了比较，并发现这三种方法之间存在普遍的一致性。我们的大样本量也允许我们研究每个种群的径向分布，我们发现cn增强的种群更加集中。我们使用C和N测量值比较了两个种群之间这些元素的演化变化，并表明两个种群对C和N的表面丰度经历了相似的演化变化。最后，我们计算了每个种群的C+N+O丰度，并将其与M10的类似测量值进行了比较；我们发现，在这两个星团中，cn增强恒星的C+N+O指数略有增强（Δ（C+N+O） ~ 0.2指数）。
We present results from a study of 94 red giant stars in the globular cluster M53. We use low-resolution spectra to measure the strength of CN and CH features at ∼3800 and 4300 Å, respectively. The strengths of these features are used to classify stars into a CN-enhanced and CN-normal population and to measure C and N abundances in all 94 stars. We find the red giant branch stars to be evenly split between the two populations identified, and observe the presence of CN-enhanced stars on the asymptotic giant branch. In addition, we identify five CH star candidates based on the strength of their CN and CH band features, and the presence of a P-branch in their CH band. We compare our identification of multiple populations to those based on the Na–O anticorrelation and pseudo-color indices in Hubble Space Telescope UV photometry, and find general agreement between all three methods. Our large sample size also allows us to study the radial distribution of each population, and we find that the CN-enhanced population is more centrally concentrated. We use our C and N measurements to compare the evolutionary changes in these elements as a function of magnitude between the two populations, and show that both populations experience similar evolutionary changes to the surface abundances of C and N. Finally, we calculate C+N+O abundances for each population and compare them to similar measurements made in M10; we find that in both clusters, CN-enhanced stars have a slightly enhanced C+N+O (Δ(C+N+O) ∼ 0.2 dex).