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CARBON-ENHANCED METAL-POOR STARS: CEMP-s and CEMP-no SUBCLASSES IN THE HALO SYSTEM OF THE MILKY WAY

机译:碳增强的贫金属星:银河系晕系统中的CEMP-s和CEMP-no子类

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We explore the kinematics and orbital properties of a sample of 323 very metal-poor stars in the halo system of the Milky Way, selected from the high-resolution spectroscopic follow-up studies of Aoki et al. and Yong et al. The combined sample contains a significant fraction of carbon-enhanced metal-poor (CEMP) stars (22% or 29%, depending on whether a strict or relaxed criterion is applied for this definition). Barium abundances (or upper limits) are available for the great majority of the CEMP stars, allowing for their separation into the CEMP-s and CEMP-no subclasses. A new method to assign membership to the inner- and outer-halo populations of the Milky Way is developed, making use of the integrals of motion, and applied to determine the relative fractions of CEMP stars in these two subclasses for each halo component. Although limited by small-number statistics, the data suggest that the inner halo of the Milky Way exhibits a somewhat higher relative number of CEMP-s stars than CEMP-no stars (57% versus 43%), while the outer halo possesses a clearly higher fraction of CEMP-no stars than CEMP-s stars (70% versus 30%). Although larger samples of CEMP stars with known Ba abundances are required, this result suggests that the dominant progenitors of CEMP stars in the two halo components were different; massive stars for the outer halo, and intermediate-mass stars in the case of the inner halo.
机译:我们探索了银河系晕圈系统中323个非常贫金属的恒星样本的运动学和轨道特性,这些样本是从Aoki等人的高分辨率光谱学后续研究中选取的。和Yong等。合并后的样本包含大量的碳增强贫金属(CEMP)星(22%或29%,具体取决于对此定义采用严格还是宽松的标准)。绝大多数CEMP恒星都有钡丰度(或上限),可以将其分为CEMP-s和CEMP-no子类。利用运动积分,开发了一种将成员分配给银河系内外晕圈成员的新方法,并将其应用于确定每个晕圈分量在这两个子类中的CEMP恒星的相对分数。尽管受到少量统计数据的限制,但数据表明,银河系的内部光晕相对于没有CEMP的恒星显示出相对较高的CEMP-s恒星相对数量(57%比43%),而外部光环具有明显的没有CEMP恒星的比例要高于CEMP恒星(70%比30%)。尽管需要更大的具有已知Ba丰度的CEMP恒星样本,但这一结果表明,两个晕分量中CEMP恒星的主要祖先是不同的。大质量恒星为外层晕,中等质量恒星为内层晕。

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