S-process in low-mass extremely metal-poor stars
| Autor: | Cruz, Monique A., Serenelli, Aldo, Weiss, Achim |
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| Rok vydání: | 2013 |
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| Druh dokumentu: | Working Paper |
| DOI: | 10.1051/0004-6361/201219513 |
| Popis: | Extremely metal-poor low-mass stars experience an ingestion of protons into the helium-rich layer during the core He-flash, resulting in the production of neutrons through the reactions ^{12}C(p,\gamma)^{13}N(\beta)^{13}C(\alpha,n)^{16}O. This is a potential site for the production of s-process elements in extremely metal-poor stars not occurring in more metal-rich counterparts. Observationally, the signatures of s-process elements in the two most iron deficient stars observed to date, HE1327-2326 & HE0107-5240, still await for an explanation. We investigate the possibility that low-mass EMP stars could be the source of s-process elements observed in extremely iron deficient stars, either as a result of self-enrichment or in a binary scenario as the consequence of a mass transfer episode. We present evolutionary and post-processing s-process calculations of a 1Msun stellar model with metallicities Z=0, 10^{-8} and 10^{-7}. We assess the sensitivity of nucleosynthesis results to uncertainties in the input physics of the stellar models, particularly regarding the details of convective mixing during the core He-flash. Our models provide the possibility of explaining the C, O, Sr, and Ba abundance for the star HE0107-5240 as the result of mass-transfer from a low-mass EMP star. The drawback of our model is that if mass would be transferred before the primary star enters the AGB phase, nitrogen would be overproduced and the ^{12}C/^{13}C abundance ratio would be underproduced in comparison to the observed values. Our results show that low-mass EMP stars cannot be ruled out as the companion stars that might have polluted HE1327-2326 & HE0107-5240 and produced the observed s-process pattern. However, more detailed studies of the core He-flash and the proton ingestion episode are needed to determine the robustness of our predictions. Comment: 12 pages, 8 figures, Accepted for publication by A&A |
| Databáze: | arXiv |
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