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arXiv 2207.05693astro-ph.GAastro-ph.SR
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研究II球状星团NGC 362中预测的金属丰度[Fe/H]变化

Investigating a predicted metallicity [Fe/H] variation in the Type II Globular Cluster NGC 362

C. Vargas, S. Villanova, D. Geisler, C. Muñoz, L. Monaco, J. O'Connell, Ata Sarajedini

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11 pages, 6 figures
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摘要：

NGC 362是一个不常见的II型银河系球状星团，显示了一个复杂的伪双色图或“染色体图”。在色星等图中，它的恒星族群明显分离，而巨恒星在染色体图中的分布则强烈暗示NGC 362可能拥有星团名义上和增强重元素丰度的恒星，其中之一可能是铁。然而，尽管之前对NGC 362进行了光谱观测，但没有检测到这种铁的变化。我们的主要目标是通过寻找[Fe/H]的任何内部变化来证实或反驳这一结果，这将使我们深入了解这个有趣的球状星团的形成和演化。本文利用安装在麦哲伦-克莱望远镜上的MIKE中阶梯光谱仪获得的高分辨率、高信噪比的光谱，对11颗红巨星分支成员进行了丰度分析。HST和GAIA测光和天体测量已被用于确定大气参数和成员。用三种不同的方法测量了目标星的T $_{\text{eff}}$、log（g）和v $_{\text{t}}$，并测量了样品的平均铁含量及其色散，得到[Fe/H] $_1$ =-1.10 $\pm0.02$，[Fe/H] $_2$ =-1.09 $\pm0.01$和[Fe/H] $_3$ =-1.10 $\pm0.01$，而内部色散分别为$σ_{[\text{Fe/H}]_1}$ =0.06 $\pm0.01$、$σ_{[\text{Fe/H}]_2}$ =0.03 $\pm0.01$和$σ_{[\text{Fe/H}]_3}$ =0.05 $\pm0.01$。误差分析给出了一个内部分散由于观测误差为0.05 dex。将观测到的分散度与内部误差进行比较，我们得出结论，NGC 362没有显示出任何内部铁扩散的痕迹。

英文摘要：

NGC 362 is a non-common Type II Galactic globular cluster, showing a complex pseudo two-color diagram or 'chromosome map'. The clear separation of its stellar populations in the color-magnitude diagram and the distribution of the giant stars in the chromosome map strongly suggests that NGC 362 could host stars with both cluster-nominal as well as enhanced heavy-element abundances, and one of them could be iron. However, despite previous spectroscopic observations of NGC 362, no such iron variation has been detected. Our main goal is to confirm or disprove this result by searching for any internal variation of [Fe/H] which would give us insight into the formation and evolution of this interesting globular cluster. In this paper, we present the abundance analysis for a sample of 11 red giant branch members based on high-resolution and high S/N spectra obtained with the MIKE echelle spectrograph mounted at the Magellan-Clay telescope. HST and GAIA photometry and astrometry has been used to determine atmospheric parameters and membership. We obtained T$_{\text{eff}}$, log(g) and v$_{\text{t}}$ for our target stars and measured the mean iron content of the sample and its dispersion with three different methods, which lead to [Fe/H]$_1$=-1.10$\pm0.02$, [Fe/H]$_2$=-1.09$\pm0.01$ and [Fe/H]$_3$=-1.10$\pm0.01$, while the internal dispersion turned out to be $σ_{[\text{Fe/H}]_1}$=0.06$\pm0.01$, $σ_{[\text{Fe/H}]_2}$=0.03$\pm0.01$ and $σ_{[\text{Fe/H}]_3}$=0.05$\pm0.01$ respectively. The error analysis gives an internal dispersion due to observational error of 0.05 dex. Comparing the observed dispersion with the internal errors, we conclude that NGC 362 does not show any trace of an internal iron spread.

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