标题： 人马座矮星系主体的化学近距离观测 显示英文标题

标题： A chemical close-up of the main body of the Sagittarius dwarf galaxy

摘要： 我们展示了属于射手座（Sgr）矮椭球星系主体残骸的37颗红巨星支（RGB）星的化学成分。所有恒星均使用FLAMES-UVES高分辨率光谱仪观测。为了避开贫金属球状星团M54恒星的污染，在Sgr的RGB蓝侧选择了23个新目标，但位于星系核外。此外，我们重新分析了十四位位于红RGB上的目标的存档光谱。对于这个样本，我们推导了21种化学元素（从氧到铕）的丰度，代表不同的核合成场所。该样本覆盖了一个广泛的金属丰度范围，从[Fe/H]～-2到～-0.4 dex，并且我们可以识别出由核心坍缩超新星（CC-SNe）和Ia型（SNe-Ia）超新星主导的富集阶段之间的过渡。观察到的[{\alpha }/Fe]趋势表明在[Fe/H]～-1.5/-1.3 dex处出现一个拐点，与Sgr相对较低的恒星形成效率相兼容。在更低的[Fe/H]时，Sgr恒星表现出与类似[Fe/H]的银河系恒星相一致的化学成分。唯一相关的例外是[Mn/Fe]、[Zn/Fe]和[Eu/Fe]。而在更高的[Fe/H]（大于～-1.5/-1.3 dex）时，Sgr的化学模式几乎在本研究分析的所有元素上显著偏离银河系的模式。一些丰度模式显示了非常大质量恒星作为超新星爆炸的贡献较低（例如[Mn/Fe]、[Zn/Fe]），Ia型超新星的亚Chandrasekhar前身星的贡献较高（例如[Ni/Fe]），以及快速中子捕获元素的高生产效率（[Eu/Fe]）。 显示英文摘要

摘要： We present the chemical composition of a sample of 37 red giant branch (RGB) stars belonging to the main body of the remnant of the Sagittarius (Sgr) dwarf spheroidal galaxy. All stars were observed with the FLAMES-UVES high-resolution spectrograph. Twenty-three new targets are selected along the blue side of the RGB of Sgr, but outside the galaxy stellar nucleus, in order to avoid contamination by the stars of the metal-poor globular cluster M54. Additionally, we re-analyzed archival spectra of fourteen targets located on the red RGB. For this sample, we derive the abundances of 21 chemical species (from Oxygen to Europium) representing different nucleosynthetic sites. The sample covers a large range of metallicity, from [Fe/H]~-2 to ~ -0.4 dex and we can identify the transition between the enrichment phases dominated by core-collapse (CC-SNe) and Type Ia (SNe-Ia) supernovae. The observed [{\alpha}/Fe] trend suggests a knee occurring at [Fe/H]~-1.5/-1.3 dex, compatible with the rather low star formation efficiency of Sgr. At lower [Fe/H], Sgr stars exhibit a chemical composition compatible with Milky Way stars of similar [Fe/H]. The only relevant exceptions are [Mn/Fe], [Zn/Fe], and [Eu/Fe]. At [Fe/H] higher than ~ -1.5/-1.3 dex, instead, the chemical pattern of Sgr significantly deviates from that of the Milky Way for almost all the elements analyzed in this study. Some of the abundance patterns reveal a lower contribution by very massive stars exploding as hypernovae (e.g. [Mn/Fe], [Zn/Fe]), a higher contribution by sub-Chandrasekhar progenitors of SNe Ia (e.g. [Ni/Fe]) and a high production efficiency of rapid neutron-capture elements ([Eu/Fe]).