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ABSTRACT The most massive stars provide an essential source of recycled material for young clusters and galaxies. While very massive stars (VMSs, M>100 $$\rm {\rm M}_{\odot }$$) are relatively rare compared to O stars, they lose disproportionately large amounts of mass already from the onset of core H-burning. VMS have optically thick winds with elevated mass-loss rates in comparison to optically thin standard O-star winds. We compute wind yields and ejected masses on the main sequence, and we compare enhanced mass-loss rates to standard ones. We calculate solar metallicity wind yields from MESA stellar evolution models in the range 50–500 $$\rm {\rm M}_{\odot }$$, including a large nuclear network of 92 isotopes, investigating not only the CNO-cycle, but also the Ne–Na and Mg–Al cycles. VMS with enhanced winds eject 5–10 times more H-processed elements (N, Ne, Na, Al) on the main sequence in comparison to standard winds, with possible consequences for observed anticorrelations, such as C–N and Na–O, in globular clusters. We find that for VMS 95 per cent of the total wind yields is produced on the main sequence, while only ∼ 5 per cent is supplied by the post-main sequence. This implies that VMS with enhanced winds are the primary source of 26Al, contrasting previous works where classical Wolf–Rayet winds had been suggested to be responsible for galactic 26Al enrichment. Finally, 200 $$\rm {\rm M}_{\odot }$$ stars eject 100 times more of each heavy element in their winds than 50 $$\rm {\rm M}_{\odot }$$ stars, and even when weighted by an IMF their wind contribution is still an order of magnitude higher than that of 50 $$\rm {\rm M}_{\odot }$$ stars.
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New Wolf–Rayet wind yields and nucleosynthesis of Helium stars
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.
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- Award ID(s):
- 1927130
- PAR ID:
- 10533843
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 533
- Issue:
- 1
- ISSN:
- 0035-8711
- Format(s):
- Medium: X Size: p. 1095-1110
- Size(s):
- p. 1095-1110
- Sponsoring Org:
- National Science Foundation
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