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

Abstract

Here 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 10(9) (in some cases 10(10)) L-circle dot. 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-(12)Ccombustion. 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 inmore » 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.« less

Authors:
 [1];  [2];  [2];  [3];  [4];  [5];  [6]
  1. Univ. of Victoria, Victoria, BC (Canada); Heidelberg Institute for Theoretical Studies, Heidelberg (Germany)
  2. Univ. of Victoria, Victoria, BC (Canada); Michigan State Univ., East Lansing, MI (United States)
  3. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  4. Hungarian Academy of Sciences, Budapest (Hungary)
  5. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Univ. of Tennessee, Knoxville, TN (United States); Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  6. Univ. of California, Santa Barbara, CA (United States)
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1329883
Alternate Identifier(s):
OSTI ID: 1345776
Report Number(s):
LA-UR-15-25096
Journal ID: ISSN 0035-8711
Grant/Contract Number:  
AC52-06NA25396; AC05-00OR22725
Resource Type:
Accepted Manuscript
Journal Name:
Monthly Notices of the Royal Astronomical Society
Additional Journal Information:
Journal Volume: 455; Journal Issue: 4; Journal ID: ISSN 0035-8711
Publisher:
Royal Astronomical Society
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; astronomy and astrophysics; stars: abundances; stars: AGB and post-AGB; stars: evolution; stars: interior

Citation Formats

Jones, Sam, Ritter, Christian, Herwig, Falk, Fryer, Christopher Lee, Pignatari, Marco, Bertolli, Michael G., and Paxton, Bill. H ingestion into He-burning convection zones in super-AGB stellar models as a potential site for intermediate neutron-density nucleosynthesis. United States: N. p., 2015. Web. doi:10.1093/mnras/stv2488.
Jones, Sam, Ritter, Christian, Herwig, Falk, Fryer, Christopher Lee, Pignatari, Marco, Bertolli, Michael G., & Paxton, Bill. H ingestion into He-burning convection zones in super-AGB stellar models as a potential site for intermediate neutron-density nucleosynthesis. United States. doi:10.1093/mnras/stv2488.
Jones, Sam, Ritter, Christian, Herwig, Falk, Fryer, Christopher Lee, Pignatari, Marco, Bertolli, Michael G., and Paxton, Bill. Thu . "H ingestion into He-burning convection zones in super-AGB stellar models as a potential site for intermediate neutron-density nucleosynthesis". United States. doi:10.1093/mnras/stv2488. https://www.osti.gov/servlets/purl/1329883.
@article{osti_1329883,
title = {H ingestion into He-burning convection zones in super-AGB stellar models as a potential site for intermediate neutron-density nucleosynthesis},
author = {Jones, Sam and Ritter, Christian and Herwig, Falk and Fryer, Christopher Lee and Pignatari, Marco and Bertolli, Michael G. and Paxton, Bill},
abstractNote = {Here 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 10(9) (in some cases 10(10)) L-circle dot. 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-(12)Ccombustion. 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.},
doi = {10.1093/mnras/stv2488},
journal = {Monthly Notices of the Royal Astronomical Society},
number = 4,
volume = 455,
place = {United States},
year = {2015},
month = {12}
}

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