Lithium on the lower red giant branch of five Galactic globular clusters
Lithium on the lower red giant branch of five Galactic globular clusters
复制标题
五个银河球状星团下红巨星分支上的锂
DOI：
10.1051/0004-6361/202141750
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发表时间：
2021
影响因子：
6.5
通讯作者：
Aguilera-Gómez C
中科院分区：
文献类型：
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作者：
Aguilera-Gómez C
锂是宇宙早期大爆炸核合成过程中产生的少数元素之一。此外，它的脆弱性使它可以作为恒星环境条件的代表。因此，旧系统中锂的丰度是各种天体物理研究的核心。低红巨星分支上的AimsStars是研究球状星团的关键，那里的主序星太暗而无法观察到。我们使用这些恒星分析的初始锂含量的集群，并将其与宇宙学的预测，以测量不同的恒星种群之间的传播李，并研究这些giants.MethodsWe使用的GIRAFFE光谱测量的锂和钠的丰度较低的红巨星分支恒星在5个球状星团的迹象。这些覆盖了广泛的范围内的金属丰度，从[Fe/H]<$-0.7到[Fe/H]<$-2.3 dex.ResultsWe发现，锂丰度在这些低红巨星分支星形成一个平台，从mA（Li）NLTE= 0.84到1.03 dex的值，没有表现出明显的相关性与金属丰度。 当使用恒星演化模型来计算这些星团的原始丰度时，我们恢复了A（Li）NLTE= 2.1 − 2.3 dex的值，与在温暖的贫金属晕星（即Spite高原）中观察到的恒定值一致。 此外，我们发现每个星团中第一和第二人口恒星的锂丰度没有差异。我们还报告在星系团NGC 3201中发现了一颗富锂巨星，A（Li）NLTE= 1.63 ± 0.18 dex，其中的富集机制可能是外部来源的污染。
ContextLithium is one of the few elements produced during Big Bang nucleosynthesis in the early universe. Moreover, its fragility makes it useful as a proxy for stellar environmental conditions. As such, the lithium abundance in old systems is at the core of various astrophysical investigations.AimsStars on the lower red giant branch are key to studies of globular clusters where main sequence stars are too faint to be observed. We use these stars to analyze the initial Li content of the clusters and compare it to cosmological predictions, to measure spreads in Li between different stellar populations, and to study signs of extra depletion in these giants.MethodsWe used the GIRAFFE spectra to measure the lithium and sodium abundances of lower red giant branch stars in five globular clusters. These cover an extensive range in metallicity, from [Fe/H] ∼ −0.7 to [Fe/H] ∼ −2.3 dex.ResultsWe find that the lithium abundance in these lower red giant branch stars forms a plateau, with values fromA(Li)NLTE= 0.84 to 1.03 dex, showing no clear correlation with metallicity. When using stellar evolutionary models to calculate the primordial abundance of these clusters, we recover values ofA(Li)NLTE= 2.1 − 2.3 dex, consistent with the constant value observed in warm metal-poor halo stars, namely the Spite plateau. Additionally, we find no difference in the lithium abundance of first and second population stars in each cluster. We also report the discovery of a Li-rich giant in the cluster NGC 3201, withA(Li)NLTE= 1.63 ± 0.18 dex, where the enrichment mechanism is probably pollution from external sources.