Chemical Abundances of M giants in the Galactic Center: a Single Metal-Rich Population with Low [alpha/Fe]
Chemical Abundances of M giants in the Galactic Center: a Single Metal-Rich Population with Low [alpha/Fe]
复制标题
银河系中心 M 巨星的化学丰度：富含单一金属且低 [α/Fe] 的族群
DOI：
10.1051/0004-6361/201424486
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发表时间：
2014
期刊：
影响因子：
--
通讯作者：
M. Schultheis
中科院分区：
文献类型：
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作者：
N. Ryde;M. Schultheis
语境。银河系核球的形成和演化在很大程度上仍然是一个悬而未决的问题。其建模中所需的最重要的可观测值之一是恒星中测量的金属丰度分布和α元素的趋势。虽然中心的 R > 50 % 以外的凸起区域已成为多次调查的目标，但由于极端灭绝和拥挤，中心部分未能进行详细研究。然而，中心的丰度梯度具有很大的诊断价值。目标。我们的目标是通过在现场探测 M 巨星，避开超巨星和星团成员来调查银河中心环境。方法。对于银心区域的9个M巨星，我们在VLT的UT1和UT3上获得了CRIRES和ISAAC同时观测到的高分辨率和低分辨率光谱。低分辨率光谱提供了确定有效温度的方法，高分辨率光谱提供了 Fe、Mg、Si 和 Ca 的详细丰度。结果。我们在 [Fe/H]=+0.11+-0.15 处发现了富含金属的群体，并且在凸起部更远处发现了缺乏金属的群体，这证实了早期的研究。然而，我们的 [α/Fe] 元素趋势显示出较低的值，遵循外部凸出趋势。发现 [Ca/Fe] 趋势可能存在异常，需要进一步研究。结论。银河系中心区域 M 巨星的分析结果排除了快速形成的情况，其中 SNIIe 在气体的化学富集中发挥了主导作用。富含金属的金属丰度和低α增强似乎表明棒状种群可能与核棒有关。
Context. The formation and evolution of the Milky Way bulge is still largely an unanswered question. One of the most essential observables needed in its modelling are the metallicity distribution and the trends of the alpha elements as measured in stars. While Bulge regions beyond R > 50 pc of the centre has been targeted in several surveys, the central part has escaped detailed study due to the extreme extinction and crowding. The abundance gradients from the center are, however, of large diagnostic value. Aims. We aim at investigating the Galactic Centre environment by probing M giants in the field, avoiding supergiants and cluster members. Methods. For 9 field M-giants in the Galactic Centre region, we have obtained high- and low-resolution spectra observed simultaneously with CRIRES and ISAAC on UT1 and UT3 of the VLT. The low-resolution spectra provide a means of determining the effective temperatures, and the high-resolution spectra provide detailed abundances of Fe, Mg, Si, and Ca. Results. We find a metal-rich population at [Fe/H]=+0.11+-0.15 and a lack of the metal-poor population, found further out in the Bulge, corroborating earlier studies. Our [alpha/Fe] element trends, however, show low values, following the outer Bulge trends. A possible exception of the [Ca/Fe] trend is found and needs further investigation. Conclusions. The results of the analysed field M-giants in the Galactic Centre region, excludes a scenario with rapid formation, in which SNIIe played a dominated role in the chemical enrichment of the gas. The metal-rich metallicities together with low alpha-enhancement seems to indicate a bar-like population perhaps related to the nuclear bar.