New Wolf-Rayet Wind Yields and Nucleosynthesis of Helium Stars

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 N-14,C-12,O-16,F-19,Ne-22,and Na-23 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 M-circle dot), 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 Al-26, we confirm that negligible Al-26 is ejected by cWRs since it has decayed to 26(Mg) or proton-captured to Al-26. However, in Paper I, we showed that very massive stars eject substantial quantities of Al-26, among other elements including N, Ne, and Na, already from the zero-age-main-sequence. Here, we examine the production of F-19 and find that even with lower mass-loss rates than previous studies, our cWR models still eject substantial amounts of F-19. We provide central neutron densities (N-n) of a 30 M-circle dot cWR compared with a 32 M-circle dot post-VMS WR and confirm that during core He-burning, cWRs produce a significant number of neutrons for the weak s-process via the Ne-22(alpha,n)Mg-25 reaction. Finally, we compare our cWR models with observed [Ne/He], [C/He], and [O/He] ratios of Galactic WC and WO stars.