Binarity among CEMP-no stars: an indication of multiple formation pathways?
Binarity among CEMP-no stars: an indication of multiple formation pathways?
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DOI：
10.1051/0004-6361/201834146
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发表时间：
2018-11
影响因子：
6.5
通讯作者：
A. Arentsen;E. Starkenburg;M. Shetrone;K. Venn;'Eric Depagne;A. McConnachie
中科院分区：
文献类型：
--
作者：
A. Arentsen;E. Starkenburg;M. Shetrone;K. Venn;'Eric Depagne;A. McConnachie
碳增强型贫金属星(CEMP)中金属丰度最低的恒星所占比例很高。CEMP-NO亚类中的恒星没有表现出任何S过程增强，因此不能很容易地用碳和S过程元素从双星AGB伴星转移来解释。我们对22颗无CEMP恒星的样本进行了径向速度监测，以进一步研究双星在这类CEMP恒星中所起的作用。我们发现了四颗新的双星CEMP--根据它们的径向速度变化没有恒星；这大大增加了已知双星的总数，达到11颗。其中一颗新发现的恒星是HE0107-5240，它是已知的最缺乏铁的恒星之一。这支持这颗恒星丰度模式起源的双星转移模型。我们在我们的样本中发现了取决于绝对碳丰度的二进制分数的不同，对于绝对碳丰度较高的恒星，二进制分数为47+15−14%，对于绝对碳丰度较低的恒星，二进制分数为18+14−9%。这可能意味着高碳丰度与贫金属星的二元性之间的关系。尽管二元性并不等同于质量转移，但双星系统中没有CEMP的恒星有可能受到污染，在解释它们的丰度模式时必须小心。我们进一步证明了GAIA在发现额外的二元候选方面的潜力。
Carbon-enhanced metal-poor (CEMP) stars comprise a high percentage of stars at the lowest metallicities. The stars in the CEMP-no subcategory do not show any s-process enhancement and therefore cannot easily be explained by transfer of carbon and s-process elements from a binary AGB companion. We have performed radial velocity monitoring of a sample of 22 CEMP-no stars to further study the role that binarity plays in this type of CEMP star. We find four new binary CEMP-no stars based on their radial velocity variations; this significantly enlarges the population of known binaries to a total of 11. One of the new stars found to be in a binary system is HE 0107–5240, which is one of the most iron-poor stars known. This supports the binary transfer model for the origin of the abundance pattern of this star. We find a difference in binary fraction in our sample that depends on the absolute carbon abundance, with a binary fraction of 47 +15−14% for stars with a higher absolute carbon abundance and 18 +14−9% for stars with a lower absolute carbon abundance. This might imply a relation between a high carbon abundance and the binarity of a metal-poor star. Although binarity does not equate to mass transfer, there is a possibility that a CEMP-no star in a binary system has been polluted, and care has to be taken in the interpretation of their abundance patterns. We furthermore demonstrate the potential of Gaia of discovering additional binary candidates.