Abundance patterns of evolved stars with Hipparcos parallaxes and ages based on the APOGEE data base
Abundance patterns of evolved stars with Hipparcos parallaxes and ages based on the APOGEE data base
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基于 APOGEE 数据库的依巴谷视差和年龄的演化恒星的丰度模式
DOI：
10.1093/mnras/stx2504
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发表时间：
2018
影响因子：
4.8
通讯作者：
Tan K. F.
中科院分区：
文献类型：
--
作者：
Jia Y. P.;Chen Y. Q.;Zhao G.;Bari M. A.;Zhao J. K.;Tan K. F.
我们调查了四组恒星在亚巨星到红团（RC）的演化阶段的丰度模式，并通过从APOGEE中提取21个单独的元素丰度和来自演化模型的年龄，借助依巴谷距离来追踪盘的化学演化。结果表明，从亚巨相向RC相，Si、S、K、Ca、Mn和Ni等6种元素的丰度变化不大。特别是，我们发现一组低[C/N]比的恒星，主要来自第二个RC星序列，表明在主RC星序列和次RC星序列之间C-N-O循环的转移效率存在差异。我们还将C-N、Mg-Al和Na-O的丰度模式与APOGEE球状星团中的巨星进行了比较，发现场星的丰度模式与富金属球状星团M107相似，[M/H]<$− 1.0，这表明以强C-N、Mg-Al和Na-O为代表的自富集机制，Mg-Al和Na-O反相关性可能并不重要，因为金属丰度达到[M/H] >-1.0 dex。根据上述6种元素的丰度和[Fe/H]，我们研究了年龄-丰度关系，并在我们的样品中发现了一些古老的超富金属星。它们的古老和富含金属的特性是恒星迁移的证据。在低[α/M]箱中年龄与金属丰度的关系显示出出乎意料的正斜率。我们认为，落入银河系圆盘的新鲜贫金属气体可能是这一意外发现的前兆。
We investigate the abundance patterns for four groups of stars at evolutionary phases from sub-giant to red clump (RC) and trace the chemical evolution of the disc by taking 21 individual elemental abundances from APOGEE and ages from evolutionary models with the aid ofHipparcosdistances. We find that the abundances of six elements (Si, S, K, Ca, Mn and Ni) are similar from the sub-giant phase to the RC phase. In particular, we find that a group of stars with low [C/N] ratios, mainly from the second sequence of RC stars, show that there is a difference in the transfer efficiency of the C-N-O cycle between the main and the secondary RC sequences. We also compare the abundance patterns of C-N, Mg-Al and Na-O with giant stars in globular clusters from APOGEE and find that field stars follow similar patterns as M107, a metal-rich globular cluster with [M/H] ∼− 1.0, which shows that the self-enrichment mechanism represented by strong C-N, Mg-Al and Na-O anti-correlations may not be important as the metallicity reaches [M/H] > −1.0 dex. Based on the abundances of above-mentioned six elements and [Fe/H], we investigate age versus abundance relations and find some old super-metal-rich stars in our sample. Their properties of old age and being rich in metal are evidence for stellar migration. The age versus metallicity relations in low-[α/M] bins show unexpectedly positive slopes. We propose that the fresh metal-poor gas infalling on to the Galactic disc may be the precursor for this unexpected finding.