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H ingestion into He-burning convection zones in super-AGB stellar models as a potential site for intermediate neutron-density nucleosynthesis

Jones, S.; Ritter, C.; Herwig, F.; Fryer, C.; Pignatari, M.; Bertolli, M. G.; Paxton, B.

Authors

S. Jones

C. Ritter

F. Herwig

C. Fryer

M. G. Bertolli

B. Paxton

Abstract

We investigate the evolution of super-AGB (SAGB) thermal pulse (TP) stars for a range of metallicities (Z) and explore the effect of convective boundary mixing (CBM). With decreasing metallicity and evolution along the TP phase, the He-shell flash and the third dredge-up (TDU) occur closer together in time. After some time (depending upon the CBM parametrization), efficient TDU begins while the pulse-driven convection zone (PDCZ) is still present, causing a convective exchange of material between the PDCZ and the convective envelope. This results in the ingestion of protons into the convective He-burning pulse. Even small amounts of CBM encourage the interaction of the convection zones leading to transport of protons from the convective envelope into the He layer. H-burning luminosities exceed 10⁹ (in some cases 10¹⁰) L⊙. We also calculate models of dredge-out in the most massive SAGB stars and show that the dredge-out phenomenon is another likely site of convective-reactive H-¹²C combustion. We discuss the substantial uncertainties of stellar evolution models under these conditions. Nevertheless, the simulations suggest that in the convective-reactive H-combustion regime of H ingestion the star may encounter conditions for the intermediate neutron capture process (i-process). We speculate that some CEMP-s/r stars could originate in i-process conditions in the H ingestion phases of low-Z SAGB stars. This scenario would however suggest a very low electron-capture supernova rate from SAGB stars. We also simulate potential outbursts triggered by such H ingestion events, present their light curves and briefly discuss their transient properties.

Journal Article Type Article
Publication Date Feb 1, 2016
Journal Monthly notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Oxford University Press (OUP)
Peer Reviewed Peer Reviewed
Volume 455
Issue 4
Pages 3848-3863
Institution Citation Jones, S., Ritter, C., Herwig, F., Fryer, C., Pignatari, M., Bertolli, M. G., & Paxton, B. (2016). H ingestion into He-burning convection zones in super-AGB stellar models as a potential site for intermediate neutron-density nucleosynthesis. Monthly notices, containing papers, abstracts of papers, and reports of the proceedings of the Society, 455(4), 3848-3863. https://doi.org/10.1093/mnras/stv2488
DOI https://doi.org/10.1093/mnras/stv2488
Keywords Stars: abundances, Stars: AGB and post-AGB, Stars: evolution, Stars: interiors
Publisher URL http://mnras.oxfordjournals.org/content/455/4/3848
Copyright Statement © 2015 The Authors
Additional Information This article has been accepted for publication in Monthly notices of the Royal Astronomical Society. ©2015 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

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