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arXiv 2205.03323astro-ph.GAastro-ph.SR
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球状星团中第一人口恒星金属丰度分布的确认

Confirmation of a metallicity spread amongst first population stars in globular clusters

Carmela Lardo, Maurizio Salaris, Santi Cassisi, Nate Bastian

备注：
9 pages, 7 figures, A&A accepted
发表信息：
A&A 662, A117 (2022)
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摘要：

大质量星团中的恒星在某些轻元素（MP）中表现出内在的变化，这些变化在相干形成情景中很难解释。近年来，HST光度测量已经导致了对多光子晶体的全局性质的表征，其细节达到了前所未有的水平。特别是，被称为染色体图的颜色-颜色图已被证明在将具有场状金属丰度分布（1 P）的星团恒星与具有独特的轻元素丰度反相关（2 P）的物体分离方面非常有效。意想不到的广泛的颜色范围所涵盖的1 P组的染色体图中的大多数调查的银河系GC最近已被归因于内在的金属丰度变化高达~0.30德克斯，从研究的SGB星在两个金属丰富的银河系GC采用适当的HST过滤器组合。另一方面，对NGC 3201和NGC 2808中1 P星小样本的高分辨率光谱分析迄今为止提供了相互矛盾的结果，在NGC 3201中检测到了金属丰度的扩散，但在NGC 2808中没有。我们提出了一种新的方法，采用HST近紫外和光学测光的RGB恒星，独立地确认这些结果。我们的方法已首次验证使用观测数据M2，GC托管一小群1 P星增强（约0.5 dex）金属丰度的主要组成部分。然后，我们将我们的方法应用于三个集群，覆盖了更大的金属丰度范围，并在其染色体图谱中，即M92，NGC 2808和NGC 6362，具有良好的人口，扩展的第一人口序列。我们确认，金属丰度的传播是存在于这些集群中的1 P恒星之间，从而固化的情况下，存在意想不到的变化高达两个因素的金属丰度在大多数GC。我们还证实了复杂的行为之间的平均金属丰度差异1 P和2 P星。

英文摘要：

Stars in massive star clusters exhibit intrinsic variations in some light elements (MPs) that are difficult to explain in a coherent formation scenario. In recent years, HST photometry has led to the characterisation of the global properties of th MPs in an unparalleled level of detail. In particular, the colour-colour diagrams known as chromosome maps have been proven to be very efficient at separating cluster stars with field-like metal abundance distribution (1P) from object with distinctive light-element abundance anti-correlations (2P). The unexpected wide colour ranges covered by the 1P group in the chromosome maps of the majority of the investigated Galactic GCs have been recently attributed to intrinsic metallicity variations up to ~0.30 dex, from the study of SGB stars in two metal rich Galactic GCs by employing appropriate HST filter combinations. On the other hand, high-resolution spectroscopy of small samples of 1P stars in NGC 3201 and NGC 2808 have so far provided conflicting results, with a spread of metallicity detected in NGC 3201 but not in NGC 2808. We present a new method that employs HST near-UV and optical photometry of RGB stars, to independently confirm these results. Our approach has been firstly validated using observational data for M2, a GC hosting a small group of 1P stars with enhanced (by ~0.5 dex) metallicity with respect to the main component. We have then applied our method to three clusters that cover a much larger metallicity range, and have well populated, extended first population sequences in their chromosome maps, namely M92, NGC2808, and NGC6362. We confirm that metallicity spreads are present among 1P stars in these clusters, thus solidifying the case for the existence of unexpected variations up to a factor of two of metal abundances in most GCs. We also confirm the complex behaviour of the mean metallicity differences between 1P and 2P stars.

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