New Wolf-Rayet wind yields and nucleosynthesis of Helium stars

TL;DR

This paper models Wolf-Rayet star winds at solar metallicity, analyzing their nucleosynthesis yields, especially for helium, fluorine, and neutron production, and compares predictions with observed stellar compositions.

Contribution

It provides updated stellar wind yields for Wolf-Rayet stars using recent hydrodynamical wind rates, focusing on nucleosynthesis and chemical enrichment during core He-burning.

Findings

cWR stars eject substantial 19F despite lower mass-loss rates

Negligible 26Al ejected by cWRs due to decay or proton capture

cWRs produce significant neutrons for the weak s-process during He-burning

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 14N, 12C, 16O, 19F, 22Ne and 23Na 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 (12-50M), adopting the recent hydrodynamical wind rates from Sander & Vink (2020). 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 26Al, we confirm that negligible 26Al is ejected by cWRs since it has decayed to 26Mg or proton-captured to 27Al. However, in Paper I, Higgins et al. (2023) we showed that very massive stars eject substantial quantities of 26Al, among other elements including N, Ne, and Na, already from the zero-age-main-sequence. Here, we examine the production of 19F and find that even with lower mass-loss rates than previous studies, our cWR models still eject substantial amounts of 19F. We provide central neutron densities (Nn) of a 30M cWR compared with a 32M post-VMS WR and confirm that during core He-burning, cWRs produce a significant number of neutrons for the weak s-process via the 22Ne(alpha,n)25Mg reaction. Finally, we compare our cWR models with observed [Ne/He], [C/He] and [O/He] ratios of Galactic WC and WO stars.