An abundance study of red-giant-branch stars in the Hercules dwarf spheroidal galaxy
An abundance study of red-giant-branch stars in the Hercules dwarf spheroidal galaxy
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武仙座矮椭球星系中红巨星分支恒星的丰度研究
DOI：
10.1051/0004-6361/201014963
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发表时间：
2010
影响因子：
6.5
通讯作者：
Adén D
中科院分区：
文献类型：
--
作者：
Adén D
矮球状星系是已知的最贫金属、最不发光的天体之一。详细的元素丰度分析的恒星在这些微弱的对象是关键，我们了解星星的形成和化学富集在早期宇宙中，并可能提供有用的信息，如何更大的星系formation.AimsOur的目的是提供一个确定的红巨星分支成员恒星的武仙座矮球状星系的[Fe/H]和[Ca/H]。在此基础上，我们探讨了武仙座主要恒星群体的年龄，以及超新星的富集历史。此外，我们的目标是提供一个新的简单的金属丰度校准Strömgren光度为贫金属，红巨星分支stars.MethodsHigh-resolution，多纤维光谱和Strömgren光度相结合，以提供尽可能多的信息，尽可能的恒星。从这一点上，我们通过求解辐射传输方程，通过marcs模型atmospheres.ResultsWe发现，红巨星分支恒星的武仙座dSph星系的金属贫比我们以前的研究是基于测光单独的估计。由此，我们得到了一个新的金属丰度校准的斯特伦格伦测光。此外，我们还发现了一个丰度趋势，即[Ca/Fe]在贫金属恒星中较高，而在富金属恒星中较低，扩散约为0.8 dex。[Ca/Fe]的趋势表明早期通过II型超新星的快速化学富集，随后是通过Ia型超新星富集为主的缓慢星星形成阶段。与等时线的比较表明武仙座的红巨星的年龄超过10 Gyr。
ContextDwarf spheroidal galaxies are some of the most metal-poor, and least luminous objects known. Detailed elemental abundance analysis of stars in these faint objects is key to our understanding of star formation and chemical enrichment in the early universe, and may provide useful information on how larger galaxies form.AimsOur aim is to provide a determination of [Fe/H] and [Ca/H] for confirmed red-giant branch member stars of the Hercules dwarf spheroidal galaxy. Based on this we explore the ages of the prevailing stellar populations in Hercules, and the enrichment history from supernovae. Additionally, we aim to provide a new simple metallicity calibration for Strömgren photometry for metal-poor, red giant branch stars.MethodsHigh-resolution, multi-fibre spectroscopy and Strömgren photometry are combined to provide as much information on the stars as possible. From this we derive abundances by solving the radiative transfer equations through marcs model atmospheres.ResultsWe find that the red-giant branch stars of the Hercules dSph galaxy are more metal-poor than estimated in our previous study that was based on photometry alone. From this, we derive a new metallicity calibration for the Strömgren photometry. Additionally, we find an abundance trend such that [Ca/Fe] is higher for more metal-poor stars, and lower for more metal-rich stars, with a spread of about 0.8 dex. The [Ca/Fe] trend suggests an early rapid chemical enrichment through supernovae of type II, followed by a phase of slow star formation dominated by enrichment through supernovae of type Ia. A comparison with isochrones indicates that the red giants in Hercules are older than 10 Gyr.