AI 中文总结
研究通过对M 星团中六颗红巨星分支恒星的高精度光谱差分分析，确认其存在多种元素丰度变化及两个恒星族群，验证先前研究，还发现族群内也有变化，并探讨其起源，认为它可能是核星团、合并产物或银河系原始构建块。
AI 中文摘要
M 22（NGC 6656）是一个化学复杂的球状星团样系统，据报道存在重元素丰度变化。然而，这些变化的程度和该星团的起源仍存在争议。在这项工作中，我们使用对六颗精心挑选的红巨星分支恒星的高质量（R = 110,000，514nm处每像素S/N = 300）VLT/UVES光谱进行逐线差分分析，来研究M 22的化学不均匀性。高精度数据验证了先前研究结果，揭示了多种元素的变化，确认该星团有两个恒星族群，除整体变化外，两个族群内部也有不可忽略的变化。我们还探讨了相关问题并将发现与星团动力学理解联系起来，认为M 22可能是核星团、两个合并星团的产物或银河系的原始构建块。
英文摘要
M 22 (NGC 6656) is a chemically complex globular cluster-like system reported to harbour heavy element abundance variations. However, the extent of these variations and the origin of this cluster is still debated. In this work, we investigate the chemical inhomogeneity of M 22 using differential line-by-line analysis of high-quality (R = 110,000, S/N = 300 per pixel at 514 nm) VLT/UVES spectra of six carefully chosen red giant branch stars. By achieving abundance uncertainties as low as ~0.01 dex (~2 per cent), this high-precision data validates the results of previous studies and reveals variations in Fe, Na, Si, Ca, Sc, Ti, Cr, Mn, Co, Ni, Zn, Y, Zr, La, Ce, Nd, Sm and Eu. Additionally, we can confirm that the cluster hosts two stellar populations with a spread of at least 0.24 dex in [Fe/H] and an average s-process abundance spread of 0.65 dex. In addition to global variations across the cluster, we also find non-negligible variations within each of the two populations, with the more metal-poor population hosting larger spreads in elements heavier than Fe than the metal-rich. We address previous works which do not identify anomalous abundances and relate our findings to our current dynamical understanding of the cluster. Given our results, we suggest that M 22 is either a nuclear star cluster, the product of two merged clusters, or an original building block of the Milky Way.
Comments18 pages, 10 figures, 7 tables. Published in MNRAS
Journal refMNRAS, 516, 3515-3531 (2022)
