Abstract
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 \({\sim }\,10^{15}\) cm\(^{-3}\)) 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.
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Notes
Notation: [A/B] = log(N\(_{A}\)/N\(_{B}\))\(_{*}\) − log(N\(_{A}\)/N\(_{B}\))\(_{\odot }\), where N\(_{A}\) and N\(_{B}\) are number densities of elements A and B respectively.
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Acknowledgements
Funding from the DST SERB project EMR/2016/005283 is gratefully acknowledged. We are thankful to Melanie Hampel for providing us with the i-process yields in the form of number fractions. This work made use of the SIMBAD astronomical database, operated at CDS, Strasbourg, France, and NASA ADS, USA.
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This article is part of the Topical Collection: Chemical elements in the Universe: Origin and evolution.
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Goswami, P.P., Goswami, A. i-Process nucleosynthesis: Observational evidences from CEMP stars. J Astrophys Astron 41, 47 (2020). https://doi.org/10.1007/s12036-020-09670-7
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DOI: https://doi.org/10.1007/s12036-020-09670-7