UVES analysis of red giants in the bulge globular cluster NGC 6522
UVES analysis of red giants in the bulge globular cluster NGC 6522
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核球球状星团 NGC 6522 中红巨星的 UVES 分析
DOI：
10.1051/0004-6361/202140815
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发表时间：
2021
影响因子：
6.5
通讯作者：
Barbuy B
中科院分区：
文献类型：
--
作者：
Barbuy B
背景NGC6522是一个中等贫金属的球状星系团([Fe/H]~−1.0)，是位于该球状星团中的若干中等贫金属蓝色水平分支星团中研究较好的代表。NGC6522丰度模式可以为银河系中部最早的化学富集提供线索。目的本研究的目的是获得轻元素C和N，α元素O，Mg，Si，Ca和Ti，奇数Z元素Na和Al，中子俘获元素Y，Zr，BA，La和ND，以及热过程元素Eu的丰度。我们验证了是否存在第一代和第二代恒星：我们发现了明显的Na-Al，Na-N和Mg-Al关联的证据，但我们无法从我们的数据中识别出Na-O反关联。方法在8M VLT UT2-Kueyen望远镜上用火焰+UVES配置的UVES和长颈鹿光谱仪获得了膨胀球状星团NGC6522中的6颗红巨星的高分辨率光谱。根据Gaiadata，原来他们中的两个是非成员，但这些也被分析了。从紫外吸收光谱出发，通过Fe- -I和Fe- -II谱线的激发和电离平衡得到了光谱参数。用光谱合成法得到了它们的丰度。结果结合前人的UVES结果，得到NGC6522的平均径向速度为Km S−1，金属丰度[Fe/H]=−1.05±0.2。α元素的平均丰度分别为：[O/Fe]=+0.38，[Mg/Fe]=≈+0.28，[Si/Fe]≈+0.19，[Ca/Fe]≈+0.13，铁峰元素[Ti/Fe]≈+0.13，热过程元素[Eu/Fe]=+0.40。中子俘获元素Y、Zr、BA和La在+0.08lt；[Y/Fe]<；+0.90，0.11<；[Zr/Fe]<；+0.50，0.00<；[Ba/Fe]<；+0.63，0.00<；[La/Fe]<；+0.45和−0.10<；[Nd/Fe]<；+0.70范围内表现出增强。我们还讨论了重元素丰度的分布。
ContextNGC 6522 is a moderately metal-poor bulge globular cluster ([Fe/H] ~ −1.0), and it is a well-studied representative among a number of moderately metal-poor blue horizontal branch clusters located in the bulge. The NGC 6522 abundance pattern can give hints on the earliest chemical enrichment in the central Galaxy.AimsThe aim of this study is to derive abundances of the light elements C and N; alpha elements O, Mg, Si, Ca, and Ti; odd-Z elements Na and Al; neutron-capture elements Y, Zr, Ba, La, and Nd; and ther-process element Eu. We verify if there are first- and second-generation stars: we find clear evidence of Na–Al, Na–N, and Mg–Al correlations, while we cannot identify the Na–O anti-correlation from our data.MethodsHigh-resolution spectra of six red giants in the bulge globular cluster NGC 6522 were obtained at the 8m VLT UT2-Kueyen telescope with both the UVES and GIRAFFE spectrographs in FLAMES+UVES configuration. In light ofGaiadata, it turned out that two of them are non-members, but these were also analysed. Spectroscopic parameters were derived through the excitation and ionisation equilibrium of Fe I and Fe II lines from UVES spectra. The abundances were obtained with spectrum synthesis. Comparisons of abundances derived from UVES and GIRAFFE spectra were carried out.ResultsThe present analysis combined with previous UVES results gives a mean radial velocity of km s−1and a metallicity of [Fe/H] = −1.05 ± 0.20 for NGC 6522. Mean abundances of alpha elements for the present four member stars are enhanced with [O/Fe] = +0.38, [Mg/Fe] = ≈+0.28, [Si/Fe] ≈ +0.19, and [Ca/Fe] ≈ +0.13, together with the iron-peak element [Ti/Fe] ≈ +0.13, and ther-process element [Eu/Fe] = +0.40. The neutron-capture elements Y, Zr, Ba, and La show enhancements in the +0.08 < [Y/Fe] < +0.90, 0.11 < [Zr/Fe] < +0.50, 0.00 < [Ba/Fe] < +0.63, 0.00 < [La/Fe] < +0.45, and −0.10 < [Nd/Fe] < +0.70 ranges. We also discuss the spread in heavy-element abundances.