Giraffe内胀调查（GIBS）II。银河系固定纬度处金属丰度分布和α元素丰度
The Giraffe Inner Bulge Survey (GIBS) II. Metallicity distributions and alpha element abundances at fixed Galactic latitude
摘要：
400颗红团巨星的高分辨率（R $\sim$ 22，500）光谱，在$\rm -4.8^{\circ} \lesssim b \lesssim -3.4^{\circ}$和$\rm -10^{\circ} \lesssim l \lesssim +10^{\circ}$的四个领域内，在吉拉菲内隆起巡天（GIBS）项目中获得。在这个样本中，我们在Baade's Window中添加了另一颗$\sim$ 400恒星，使用相同的仪器配置进行观察。我们构建了整个样品的金属丰度分布，以及为每个字段单独，为了调查梯度或字段到字段的分布形状的变化的存在。在五个领域的金属丰度分布是一致的，从一个单一的父人口，表明没有梯度沿银河酒吧的主轴。全球金属丰度分布符合两个高斯分布。贫金属组分相当广泛，平均值为$\rm <[Fe/H]>=-0.31$ dex和$σ=0.31$ dex。富金属区较窄，平均$\rm <[Fe/H]>=+0.26$和$σ=0.2$ dex。[Mg/Fe]比遵循与[Fe/H]紧密的趋势，在贫金属制度中相对于太阳增强，类似于在局部厚盘中观察到的巨星。[Ca[Mg/Fe]丰度遵循类似的趋势，但比[Mg/Fe]分散得多。在$\rm [Fe/H]=-0.44$ dex下观察到[Mg/Fe]降低。这\textit{knee}是在协议与我们以前的凸起的研究K-巨星沿短轴，但0.1德克斯低于金属比一个报告的凸起微透镜矮星和亚巨星。我们发现$α$元素丰度分布在不同领域之间没有变化。
英文摘要：
High resolution (R$\sim$22,500) spectra for 400 red clump giants, in four fields within $\rm -4.8^{\circ} \lesssim b \lesssim -3.4^{\circ}$ and $\rm -10^{\circ} \lesssim l \lesssim +10^{\circ}$, were obtained within the GIRAFFE Inner Bulge Survey (GIBS) project. To this sample we added another $\sim$ 400 stars in Baade's Window, observed with the identical instrumental configuration. We constructed the metallicity distributions for the entire sample, as well as for each field individually, in order to investigate the presence of gradients or field-to-field variations in the shape of the distributions. The metallicity distributions in the five fields are consistent with being drawn from a single parent population, indicating the absence of a gradient along the major axis of the Galactic bar. The global metallicity distribution is well fitted by two Gaussians. The metal poor component is rather broad, with a mean at $\rm <[Fe/H]>=-0.31$ dex and $σ=0.31$ dex. The metal-rich one is narrower, with mean $\rm <[Fe/H]>=+0.26$ and $σ=0.2$ dex. The [Mg/Fe] ratio follows a tight trend with [Fe/H], with enhancement with respect to solar in the metal-poor regime, similar to the one observed for giant stars in the local thick disc. [Ca/Fe] abundances follow a similar trend, but with a considerably larger scatter than [Mg/Fe]. A decrease in [Mg/Fe] is observed at $\rm [Fe/H]=-0.44$ dex. This \textit{knee} is in agreement with our previous bulge study of K-giants along the minor axis, but is 0.1 dex lower in metallicity than the one reported for the Bulge micro lensed dwarf and sub-giant stars. We found no variation in $α$-element abundance distributions between different fields.
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