Nucleosynthesis Predictions for Intermediate-Mass AGB Stars: Comparison to Observations of Type I Planetary Nebulae - AstrophysicsReportar como inadecuado




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Abstract: Type I planetary nebulae PNe have high He-H and N-O ratios and are thoughtto be descendants of stars with initial masses of ~3-8Msun. Thesecharacteristics indicate that the progenitor stars experienced proton-capturenucleosynthesis at the base of the convective envelope, in addition to the slowneutron capture process operating in the He-shell the s-process. We comparethe predicted abundances of elements up to Sr from models of intermediate-massasymptotic giant branch AGB stars to measured abundances in Type I PNe. Inparticular, we compare predictions and observations for the light trans-ironelements Se and Kr, in order to constrain convective mixing and the s-processin these stars. A partial mixing zone is included in selected models to explorethe effect of a 13C pocket on the s-process yields. The solar-metallicitymodels produce enrichments of Se, Kr-Fe < 0.6, consistent with GalacticType I PNe where the observed enhancements are typically < 0.3 dex, while lowermetallicity models predict larger enrichments of C, N, Se, and Kr. Odestruction occurs in the most massive models but it is not efficient enough toaccount for the > 0.3 dex O depletions observed in some Type I PNe. It is notpossible to reach firm conclusions regarding the neutron source operating inmassive AGB stars from Se and Kr abundances in Type I PNe; abundances for mores-process elements may help to distinguish between the two neutron sources. Wepredict that only the most massive models would evolve into Type I PNe,indicating that extra-mixing processes are active in lower-mass stars3-4Msun, if these stars are to evolve into Type I PNe.



Autor: Amanda I. Karakas, Mark A. van Raai, Maria Lugaro, N. C. Sterling, Harriet L. Dinerstein

Fuente: https://arxiv.org/



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