First stars X. The nature of three unevolved Carbon-Enhanced Metal-Poor stars ⋆
First stars X. The nature of three unevolved Carbon-Enhanced Metal-Poor stars ⋆
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DOI：
10.1051/0004-6361:20065440
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发表时间：
2006-08
影响因子：
6.5
通讯作者：
T. Sivarani;T. Beers;P. Bonifacio;P. Molaro;R. Cayrel;F. Herwig;M. Spite;F. Spite;B. Plez;J. Andersen;B. Barbuy;É. Depagne;V. Hill;P. François;B. Nordstrom;F. Primas
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文献类型：
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作者：
T. Sivarani;T. Beers;P. Bonifacio;P. Molaro;R. Cayrel;F. Herwig;M. Spite;F. Spite;B. Plez;J. Andersen;B. Barbuy;É. Depagne;V. Hill;P. François;B. Nordstrom;F. Primas
上下文银河系中大约20%的贫金属恒星表现出大量的碳增强。重要的是要确定哪些天体物理学的网站和过程是负责的元素丰度模式的早期银河系人口。目标。基于详细的丰度分析，我们试图了解三颗主序星（CS 31080-095、CS 22958-042和CS 29528-041）的祖先的性质。方法.从高分辨率VLT/UVES光谱（R类似于43000），我们确定了Li，C，N，O和其他重要元素的丰度或上限，以及C-12/C-13同位素比值。结果这三颗恒星都有-3.30 <= [Fe/H]<= -2.85和中等到高的CNO丰度。CS 22958-042是已知的最富碳的CEMP恒星之一（[C/Fe] = +3.2），而CS 29528-041（已知的少数几颗氮增强贫金属恒星之一）是最富氮的恒星之一（[N/Fe] = +3.0）。CS 31080-095（[O/Fe] = +2.35）和CS 22958-042（[O/Fe] = +1.35）中的氧含量非常高。这三颗恒星的[Sr/Fe]都小于0;在CS 22958-042中没有检测到Ba（[Ba/Fe]小于-0.53），但在另外两颗恒星中有适度的增强（[Ba/Fe]近似于1）。CS 22958-042显示了迄今在CEMP恒星中发现的最大的钠过量（[Na/Fe] = +2.8）。CS 22958-042的C-12/C-13 = 9，类似于大多数没有增强中子捕获元素的CEMP星，而CS 31080-095的C-12/C-13 = 40。CS 31080-095和CS 29528-041的A（Li）与1.7相似，低于Spite平台，而CS 22958-042中未检出Li。结论. CS 22958-042是一颗CEMP-no星星，但另外两颗恒星并不属于已知的CEMP星星类别，因此它们要么构成了一个新的类别，要么是CEMP-no和CEMP-s类别之间的联系，增加了CEMP恒星丰度模式的复杂性。我们解释我们的恒星中的丰度模式，这意味着目前假定的AGB二进制祖先的模型缺乏额外的混合过程，类似于那些显然在RGB星。（减）
Context. On the order of 20% of the very metal-poor stars in the Galaxy exhibit large carbon enhancements. It is important to establish which astrophysical sites and processes are responsible for the elemental abundance patterns of this early Galactic population. Aims. We seek to understand the nature of the progenitors of three main-sequence turnoff Carbon-Enhanced Metal-Poor (CEMP) stars, CS 31080-095, CS 22958-042, and CS 29528-041, based on a detailed abundance analysis. Methods. From high-resolution VLT/UVES spectra (R similar to 43 000), we determine abundances or upper limits for Li, C, N, O, and other important elements, as well as C-12/C-13 isotopic ratios. Results. All three stars have -3.30 <= [Fe/H]<= -2.85 and moderate to high CNO abundances. CS 22958-042 is one of the most carbon-rich CEMP stars known ([C/Fe] = +3.2), while CS 29528-041 (one of the few N-enhanced metal-poor stars known) is one of the most nitrogen rich ([N/Fe] = +3.0). Oxygen is very high in CS 31080-095 ([O/Fe] = +2.35) and in CS 22958-042 ([O/Fe] = +1.35). All three stars exhibit [Sr/Fe] < 0; Ba is not detected in CS 22958-042 ([Ba/Fe] < -0.53),but it is moderately enhanced ([Ba/Fe] similar to 1) in the other two stars. CS 22958-042 displays one of the largest sodium overabundances yet found in CEMP stars ([Na/Fe] = +2.8). CS 22958-042 has C-12/C-13 = 9, similar to most other CEMP stars without enhanced neutron-capture elements, while C-12/C-13 = 40 in CS 31080-095. CS 31080-095 and CS 29528-041 have A(Li) similar to 1.7, below the Spite Plateau, while Li is not detected in CS 22958-042. Conclusions. CS 22958-042 is a CEMP-no star, but the other two stars are in no known class of CEMP star and thus either constitute a new class or are a link between the CEMP-no and CEMP-s classes, adding complexity to the abundance patterns for CEMP stars. We interpret the abundance patterns in our stars to imply that current models for the presumed AGB binary progenitors lack an extra-mixing process, similar to those apparently operating in RGB stars. (Less)