Two distinct halo populations in the solar neighborhood. II. Evidence from stellar abundances of Mn, Cu, Zn, Y, and Ba
Two distinct halo populations in the solar neighborhood. II. Evidence from stellar abundances of Mn, Cu, Zn, Y, and Ba
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DOI：
10.1051/0004-6361/201116619
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发表时间：
2011-03
影响因子：
6.5
通讯作者：
P. Nissen;W. Schuster
中科院分区：
文献类型：
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作者：
P. Nissen;W. Schuster
先前的一项研究（Nissen & Schuster 2010）对94颗-1.6 < [Fe/H] < -0.4的矮星进行了研究，发现在给定的金属丰度下存在两种不同的晕族，它们的[α /Fe]有系统的差异。在这项工作的继续，锰、铜、锌、Y和钡的丰度被确定为相同的恒星样本。通过高分辨率VLT/UVES和NOT/FIES光谱测量原子谱线的等效宽度，并利用基于MARCS模型大气的LTE分析得出精确的丰度比。[Cu/Fe]、[Zn/Fe]和[Ba/Y]的“高α”和“低α”晕族之间存在系统差异，而[Mn/Fe]的“高α”晕族与“低α”晕族之间没有显著差异。在给定的金属丰度下，[Cu/Fe]显示出与[Na/Fe]和[Ni/Fe]中相应的散射密切相关的大散射。如果高α恒星形成于恒星形成速率如此之高的区域，以至于只有大质量恒星和II型超新星对化学富集有贡献，那么[Cu/Fe]、[Zn/Fe]和[Ba/Y]的金属丰度趋势可以从现有的核合成计算中解释。另一方面，低α恒星很可能起源于化学演化较慢的系统，其特征是Ia型超新星和低质量AGB恒星的额外富集。
A previous study (Nissen & Schuster 2010) of 94 dwarf stars with -1.6 < [Fe/H] < -0.4 has revealed the existence of two distinct halo populations with a systematic difference in [alpha/Fe] at a given metallicity. In continuation of that work, abundances of Mn, Cu, Zn, Y, and Ba are determined for the same sample of stars. Equivalent widths of atomic lines are measured from high resolution VLT/UVES and NOT/FIES spectra and used to derive precise abundance ratios from an LTE analysis based on MARCS model atmospheres. Systematic differences between the `high-alpha' and `low-alpha' halo populations are found for [Cu/Fe], [Zn/Fe], and [Ba/Y], whereas there is no significant difference in the case of [Mn/Fe]. At a given metallicity, [Cu/Fe] shows a large scatter that is closely correlated with a corresponding scatter in [Na/Fe] and [Ni/Fe]. The metallicity trends of [Cu/Fe], [Zn/Fe], and [Ba/Y] can be explained from existing nucleosynthesis calculations if the high-alpha stars formed in regions with such a high star formation rate that only massive stars and Type II supernovae contributed to the chemical enrichment. The low-alpha stars, on the other hand, most likely originate from systems with a slower chemical evolution, characterized by additional enrichment from Type Ia supernovae and low-mass AGB stars.