New Wolf–Rayet wind yields and nucleosynthesis of Helium stars

Higgins, Erin R; Vink, Jorick S; Hirschi, Raphael; Laird, Alison M; Sander, Andreas A C

Abstract

Strong metallicity-dependent winds dominate the evolution of core He-burning, classical Wolf–Rayet (cWR) stars, which eject both H and He-fusion products such as $^{14}$N, $^{12}$C, $^{16}$O, $^{19}$F, $^{22}$Ne, and $^{23}$Na during their evolution. The chemical enrichment from cWRs can be significant. cWR stars are also key sources for neutron production relevant for the weak s-process. We calculate stellar models of cWRs at solar metallicity for a range of initial Helium star masses (12–50 $\rm M_{\odot }$), adopting recent hydrodynamical wind rates. Stellar wind yields are provided for the entire post-main sequence evolution until core O-exhaustion. While literature has previously considered cWRs as a viable source of the radioisotope $^{26}$Al, we confirm that negligible $^{26}$Al is ejected by cWRs since it has decayed to $^{26}$Mg or proton-captured to $^{27}$Al. However, in Paper I, we showed that very massive stars eject substantial quantities of $^{26}$Al, among other elements including N, Ne, and Na, already from the zero-age-main-sequence. Here, we examine the production of $^{19}$F and find that even with lower mass-loss rates than previous studies, our cWR models still eject substantial amounts of $^{19}$F. We provide central neutron densities (N$_{n}$) of a 30 $\rm M_{\odot }$ cWR compared with a 32 $\rm M_{\odot }$ post-VMS WR and confirm that during core He-burning, cWRs produce a significant number of neutrons for the weak s-process via the $^{22}$Ne($\alpha$,n)$^{25}$Mg reaction. Finally, we compare our cWR models with observed [Ne/He], [C/He], and [O/He] ratios of Galactic WC and WO stars.

Citation

Higgins, E. R., Vink, J. S., Hirschi, R., Laird, A. M., & Sander, A. A. C. (2024). New Wolf–Rayet wind yields and nucleosynthesis of Helium stars. Monthly Notices of the Royal Astronomical Society, 533(1), 1095-1110. https://doi.org/10.1093/mnras/stae1853

• Journal Article Type: Article
• Acceptance Date: Jul 10, 2024
• Online Publication Date: Aug 8, 2024
• Publication Date: Aug 7, 2024
• Deposit Date: Sep 2, 2024
• Journal: Monthly Notices of the Royal Astronomical Society
• Print ISSN: 0035-8711
• Publisher: Oxford University Press
• Peer Reviewed: Peer Reviewed
• Volume: 533
• Issue: 1
• Pages: 1095-1110
• DOI: https://doi.org/10.1093/mnras/stae1853
• Keywords: nuclear reactions, nucleosynthesis, abundances, stars: abundances, stars: evolution, stars: interiors, stars: massive, stars: mass loss
• Public URL: https://keele-repository.worktribe.com/output/889991
• Publisher URL: https://academic.oup.com/mnras/article/533/1/1095/7730258