Ruoyun Huang, Baitian Tang, Chengyuan Li, Doug Geisler, Mario Mateo, Ying-Yi Song, Holger Baumgardt, Julio A. Carballo-Bello, Yue Wang, Jundan Nie, Bruno Dias, José G. Fernández-Trincado
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引用次数: 0
摘要
星团历来被认为是简单的恒星群,所有恒星都具有相同的年龄和初始化学成分。然而,球状星团(GCs)中出现的化学反常现象,即多恒星群(MPs),对致密环境中的恒星形成理论提出了挑战。文献研究表明,质量、金属性和年龄可能是多恒星群表现的控制参数。在物理参数空间中确定有/无多恒星的星团之间的界限,对于揭示多恒星存在背后的驱动机制至关重要。在这项研究中,我们在传统上被认为是年轻 GC 的 Whiting 1 中寻找 MP 信号。利用麦哲伦望远镜,我们获得了惠廷 1 号八个巨星在 λλ = 3850-5500 Å 范围内的低分辨率光谱。我们根据 CN 和 CH 光谱指数测量了 C 和 N 丰度。C 丰度和 N 丰度的变化与其测量误差相当(∼ 0.1 dex),表明惠廷 1 号不存在 MPs。结合这些发现和文献研究,我们提出了金属性与星团紧密度指数参数空间的一个极限,它能相对清晰地将有/无MPs的星团(GCs/开放星团)区分开来。这个极限是以物理为基础的。在更大的尺度上,星系环境决定了星团的紧密度和金属度,从而导致了富含金属、弥散的、原地形成的古老星团。我们提出的极限还影响到我们对人马座矮星系形成过程的理解:在第一次恒星爆发(年龄≲ 8-10 Gyr)之后形成的星团。这些星团是简单的恒星群,因为富集的星系环境不再适合形成MP。
Star clusters were historically considered simple stellar populations, with all stars sharing the same age and initial chemical composition. However, the presence of chemical anomalies in globular clusters (GCs), called multiple stellar populations (MPs), has challenged star formation theories in dense environments. Literature studies show that mass, metallicity, and age are likely controlling parameters for the manifestation of MPs. Identifying the limit between clusters with/without MPs in physical parameter space is crucial to reveal the driving mechanism behind their presence. In this study, we look for MP signals in Whiting 1, which is traditionally considered a young GC. Using the Magellan telescope, we obtained low-resolution spectra within λλ = 3850–5500 Å for eight giants of Whiting 1. We measured the C and N abundances from the CN and CH spectral indices. C and N abundances have variations comparable with their measurement errors (∼ 0.1 dex), suggesting that MPs are absent from Whiting 1. Combining these findings with literature studies, we propose a limit in the metallicity vs. cluster compactness index parameter space, which relatively clearly separates star clusters with/without MPs (GCs/open clusters). This limit is physically motivated. On a larger scale, the galactic environment determines cluster compactness and metallicity, leading to metal-rich, diffuse, old clusters formed ex situ. Our proposed limit also impacts our understanding of the formation of the Sagittarius dwarf galaxy: star clusters formed after the first starburst (age≲ 8–10 Gyr). These clusters are simple stellar populations because the enriched galactic environment is no longer suitable for MP formation.
期刊介绍:
Science China Physics, Mechanics & Astronomy, an academic journal cosponsored by the Chinese Academy of Sciences and the National Natural Science Foundation of China, and published by Science China Press, is committed to publishing high-quality, original results in both basic and applied research.
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