基于UVES数据的银核中Na、Mg和Al的化学演化

中文摘要 AI 辅助

银核的形成机制尚未完全明确，有证据表明其包含不同的恒星族群，包括由旋臂棒驱动的成分、内盘成分以及更古老的椭球星系成分。化学丰度为这些族群的起源提供了关键约束，尤其是对于Na、Al这类奇数Z元素以及Mg，它们在高金属丰度下的行为仍存在争议。本研究旨在调查银核恒星中Na、Mg和Al是否存在丰度过剩，重点关注富金属区域，并评估其与化学演化模型预测的一致性。我们重新计算了文献中先前分析的55颗银核红巨星的Na、Mg和Al丰度。本研究基于欧洲南方天文台甚大望远镜获取的高分辨率UVES光谱，采用Turbospectrum代码进行光谱合成，并使用更新的原子和分子线表。我们发现，在富金属端，Mg和Al的丰度略低于先前的研究，而仍有一部分富金属恒星表现出显著的Na丰度增强。当采用不同的恒星参数时，这些增强仍然存在，表明其具有稳健性。高金属丰度下存在Na丰度增强的恒星难以与标准化学演化模型相协调，这暗示银核中存在额外的增丰过程，或恒星产量随金属丰度呈现特殊行为。Na丰度增强可能是由于大质量恒星产生的金属丰度依赖型产量（现有模型未考虑），和/或渐近巨支（AGB）恒星的增丰，或来自球状星团蒸发的第二代恒星，后一种可能性的依据是，对于富金属（[Fe/H]>0）恒星，似乎存在Na-O反相关关系。

英文摘要

The formation of the Galactic bulge remains incompletely understood, with evidence pointing to different stellar populations, including a bar-driven component, an inner-disk population, and an older spheroidal component. Chemical abundances provide critical constraints on the origin of these populations, particularly for odd-Z elements such as Na and Al, as well as Mg, whose behaviour at high metallicity is still a matter of debate. We aim to investigate the presence of overabundances of Na, Mg, and Al in Galactic bulge stars, with particular emphasis on the metal-rich regime, and to evaluate their consistency with predictions from chemical evolution models. We re-derived the abundances of Na, Mg, and Al for a sample of 55 bulge red giants previously analysed in the literature. Our study is based on high-resolution UVES spectra obtained with the ESO Very Large Telescope and employs spectrum synthesis using the Turbospectrum code, with updated atomic and molecular line lists. We find somewhat lower abundances of Mg and Al at the metal-rich end than previous studies, while a fraction of the metal-rich stars still exhibit significant Na enhancements. These enhancements persist when different sets of stellar parameters are adopted, indicating that they are robust. The presence of Na-enhanced stars at high metallicity is difficult to reconcile with standard chemical evolution models and suggests additional enrichment processes in the bulge, or a particular behaviour of stellar yields with metallicity. The Na enhancement could be due to metallicity-dependent yields from massive stars, not taken into account in available models, and/or enrichment by asymptotic giant branch stars, or due to second-generation stars evaporated from globular clusters, the latter option arising because for the metal-rich ([Fe/H]>0) stars a Na-O anti-correlation appears to occur.

发表机构

• Universidade de São Paulo（圣保罗大学）
• Astrophysikalisches Institut Potsdam（波茨坦天体物理研究所）
• Université de Sophia-Antipolis, Observatoire de la Côte d’Azur（索菲亚-安提贝斯大学，蔚蓝海岸天文台）
• Universidad Catolica de Chile（智利天主教大学）
• INAF-Osservatorio Astronomico di Padova（意大利国家天体物理研究所帕多瓦天文台）
• Instituto de Astronomía, Universidad Nacional Autónoma de México（墨西哥国立自治大学天文学研究所）
• Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences（波兰科学院尼古拉·哥白尼天文学中心）
• Max Planck Institute for Astronomy（马克斯·普朗克天文学研究所）
• Landessternwarte, Zentrum für Astronomie der Universität Heidelberg（海德堡大学州立天文台，天文学中心）
• Fakultät für Physik und Astronomie, Universität Heidelberg（海德堡大学物理与天文学院）

机构由 AI 辅助整理，请以论文原文为准。

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15 pages, 9 figures