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i-Process nucleosynthesis: Observational evidences from CEMP stars
Journal of Astrophysics and Astronomy ( IF 1.1 ) Pub Date : 2020-12-01 , DOI: 10.1007/s12036-020-09670-7
Partha Pratim Goswami , Aruna Goswami

The surface chemical compositions of a large fraction of carbon-enhanced metal-poor (CEMP) stars, the so-called CEMP-r/s stars, are known to exhibit enhancement of both s-process and r-process elements. For these stars, the heavy-element abundances cannot be explained either by s-process or r-process nucleosynthesis alone, as the production sites of s-process and r-process elements are very different, and these two processes produce distinct abundance patterns. Thus, the observational evidence of the double enhancement seen in CEMP-r/s stars remains a puzzle as far as the origin of the elements is concerned. In this work, we have critically analysed the observed abundances of heavy elements in a sample of eight CEMP-r/s stars from the literature to trace the origin of the observed double enhancement. Towards this, we have conducted a parametric-model-based analysis to delineate the contributions of s-process and r-process nucleosynthesis to the observed elemental abundances. We have further examined if the i-process (intermediate-process) nucleosynthesis that occurs at high neutron density (n $${\sim }\,10^{15}$$ ∼ 10 15 cm $$^{-3}$$ - 3 ) produced during proton ingestion from a H-rich envelope to the intershell region of an AGB star, which is capable of producing both r-process and s-process elements in a single stellar site, could explain the observed abundance patterns of the sample stars. Our analysis shows that the observed abundance patterns of the selected sample of CEMP-r/s stars could be fairly well reproduced using the i-process model yields.

中文翻译:

i-Process 核合成:来自 CEMP 恒星的观测证据

大部分碳增强贫金属 (CEMP) 星,即所谓的 CEMP-r/s 星,其表面化学成分都表现出 s 过程和 r 过程元素的增强。对于这些恒星,重元素丰度不能单独用 s 过程或 r 过程核合成来解释,因为 s 过程和 r 过程元素的产生地点非常不同,这两种过程产生不同的丰度模式。因此,就元素的起源而言,在 CEMP-r/s 恒星中看到的双重增强的观测证据仍然是一个谜。在这项工作中,我们批判性地分析了文献中八颗 CEMP-r/s 恒星样本中观测到的重元素丰度,以追踪观测到的双增强的起源。对此,我们进行了基于参数模型的分析,以描绘 s 过程和 r 过程核合成对观察到的元素丰度的贡献。我们进一步检查了在高中子密度 (n $${\sim }\,10^{15}$$ ∼ 10 15 cm $$^{-3}$ $ - 3 ) 从富含 H 的包层到 AGB 恒星壳间区域的质子摄取过程中产生的,它能够在单个恒星位点产生 r 过程和 s 过程元素,可以解释观察到的丰度模式样本星星。我们的分析表明,使用 i-process 模型产量可以很好地再现所选 CEMP-r/s 恒星样本的观测丰度模式。
更新日期:2020-12-01
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