arXiv 1706.053132017-06-16astro-ph.SR

CEMP-无源星的超新星前混合

Pre-supernova mixing in CEMP-no source stars

Arthur Choplin, Sylvia Ekström, Georges Meynet, André Maeder, Cyril Georgy, Raphael Hirschi

备注：: 17 pages, 12 figures, Accepted for publication in A&A
发表信息：: A&A 605, A63 (2017)
DOI：: 10.1051/0004-6361/201630182

摘要：

上下文CEMP-no星是一种寿命较长的低质量恒星，铁含量非常低，碳过量，没有或只有轻微的s或r元素存在的迹象。虽然它们的起源仍然是一个有争议的问题，但它们通常被认为是由前一代恒星（源星）喷出的物质构成的。目的。我们从观测到的CEMP-无星的丰度数据对源星进行了约束。方法.我们计算了20，32和60 M $_{\odot}$的源星模型，Z = 10 $^{-5}$，有和没有快速旋转。对于每个模型，我们还计算了一个情况下，后期混合事件之间发生的氢和氦燃烧壳$\sim$ 200年前结束的演变。这在源星中创建了一个部分hoc处理的区域。我们使用在CEMP-no星上观察到的12 C/13 C和C/N比来限制可能的源星（质量，后期混合与否）。然后，我们更仔细地检查了6颗CEMP-无星的丰度数据，并选择了它们的首选源星。结果在所研究的六颗CEMP-no星中，有四颗在没有源星后期混合过程的情况下无法解释。其中两个显示了源星中渐进混合（例如由于旋转）的核合成特征。我们还表明，一个20 M的$_{\odot}$源星是首选相比，60 M的$_{\odot}$之一，可能只有外层的源星被驱逐，以重现所观察到的12 C/13 C。结论.结果表明：（1）在某些源星中可能存在晚期混合过程;（2）在几颗源星中可能存在渐进混合过程，可能是由快速自转实现的;（3）与$\sim$ 60 M $_{\odot}$源星相比，$\sim$ 20 M $_{\odot}$源星更受青睐;（4）源星可能优先经历了一颗具有较大回落的低能超新星。

英文摘要：

Context. CEMP-no stars are long-lived low-mass stars with a very low iron content, overabundances of carbon and no or minor signs for the presence of s- or r-elements. Although their origin is still a matter of debate, they are often considered as being made of a material ejected by a previous stellar generation (source stars). Aims. We place constraints on the source stars from the observed abundance data of CEMP-no stars. Methods. We computed source star models of 20, 32, and 60 M$_{\odot}$ at Z = 10$^{-5}$ with and without fast rotation. For each model we also computed a case with a late mixing event occurring between the hydrogen and helium-burning shell $\sim$ 200 yr before the end of the evolution. This creates a partially CNO-processed zone in the source star. We use the 12C/13C and C/N ratios observed on CEMP-no stars to put constraints on the possible source stars (mass, late mixing or not). Then, we inspect more closely the abundance data of six CEMP-no stars and select their preferred source star(s). Results. Four out of the six CEMP-no stars studied cannot be explained without the late mixing process in the source star. Two of them show nucleosynthetic signatures of a progressive mixing (due e.g. to rotation) in the source star. We also show that a 20 M$_{\odot}$ source star is preferred compared to one of 60 M$_{\odot}$ and that likely only the outer layers of the source stars were expelled to reproduce the observed 12C/13C. Conclusions. The results suggest that (1) a late mixing process could operate in some source stars, (2) a progressive mixing, possibly achieved by fast rotation, is at work in several source stars, (3) $\sim$ 20 M$_{\odot}$ source stars are preferred compared to $\sim$ 60 M$_{\odot}$ ones, and (4) the source star might have preferentially experienced a low energetic supernova with large fallback.

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