Chromium Nucleosynthesis and Silicon-Carbon Shell Mergers in Massive Stars

Côté, Benoit; Jones, Samuel; Herwig, Falk; Pignatari, Marco

Abstract

We analyze the production of the element Cr in galactic chemical evolution (GCE) models using the NuGrid nucleosynthesis yields set. We show that the unusually large [Cr/Fe] abundance at [Fe/H] ≈ 0 reported by previous studies using those yields and predicted by our Milky Way model originates from the merging of convective Si-burning and C-burning shells in a 20 {M}_{\odot } model at metallicity Z = 0.01, about an hour before the star explodes. This merger mixes the incomplete burning material in the Si shell, including 51V and 52Cr, out to the edge of the carbon/oxygen (CO) core. The adopted supernova model ejects the outer 2 {M}_{\odot } of the CO core, which includes a significant fraction of the Cr-rich material. When including this 20 M ⊙ model at Z = 0.01 in the yields interpolation scheme of our GCE model for stars between 15 and 25 {M}_{\odot }, we overestimate [Cr/Fe] by an order of magnitude at [Fe/H] ≈ 0 relative to observations in the Galactic disk. This raises a number of questions regarding the occurrence of Si–C shell mergers in nature, the accuracy of different simulation approaches, and the impact of such mergers on the presupernova structure and explosion dynamics. According to the conditions in this 1D stellar model, the substantial penetration of C-shell material into the Si shell could launch a convective–reactive global oscillation if a merger does take place. In any case, GCE provides stringent constraints on the outcome of this stellar evolution phase.

Citation

Côté, B., Jones, S., Herwig, F., & Pignatari, M. (2020). Chromium Nucleosynthesis and Silicon-Carbon Shell Mergers in Massive Stars. The Astrophysical journal, 892(1), Article 57. https://doi.org/10.3847/1538-4357/ab77ac

• Journal Article Type: Article
• Acceptance Date: Feb 17, 2020
• Online Publication Date: Mar 27, 2020
• Publication Date: Mar 20, 2020
• Deposit Date: Mar 31, 2020
• Publicly Available Date: Apr 1, 2020
• Journal: Astrophysical Journal
• Print ISSN: 0004-637X
• Electronic ISSN: 1538-4357
• Publisher: American Astronomical Society
• Peer Reviewed: Peer Reviewed
• Volume: 892
• Issue: 1
• Article Number: 57
• DOI: https://doi.org/10.3847/1538-4357/ab77ac
• Keywords: Galaxy chemical evolution; Chemical enrichment; Stellar abundances; Massive stars ; Chemical abundances; Stellar nucleosynthesis; Galaxy abundances; Stellar evolutionary models
• Public URL: https://hull-repository.worktribe.com/output/3482228
• Publisher URL: https://iopscience.iop.org/article/10.3847/1538-4357/ab77ac
• Additional Information: Journal title: The Astrophysical Journal; Article type: paper; Article title: Chromium Nucleosynthesis and Silicon–Carbon Shell Mergers in Massive Stars; Copyright information: © 2020. The American Astronomical Society. All rights reserved.; Date received: 2019-06-11; Date accepted: 2020-02-17; Online publication date: 2020-03-27