paper

Evolution of stars with 60 and 200 Msun: predictions for WNh stars in the Milky Way

arXiv:2407.14165 · doi:10.1051/0004-6361/202451565

Abstract

We study in detail the evolution of two massive stars at solar metallicity (), by calculating their final masses, radial expansion, and chemical enrichment. We run evolutionary models for initial masses 60 and 200 , using MESA and the Geneva-evolution-code (GENEC). For the mass loss, we adopt the self-consistent m-CAK prescription for the optically thin winds of OB-type stars, a semi-empirical formula for H-rich optically thick wind of WNh stars, and a hydrodynamically consistent formula for the H-poor thick wind of classical Wolf-Rayet stars. The transition from thin to thick winds is set at . For the 60 case, the GENEC model predicts a more efficient rotational mixing and more chemically homogeneous evolution, whereas the MESA model predicts a large radial expansion reaching the LBV phase. For the 200 case, differences between both evolution codes are less relevant because their evolution is dominated by wind mass loss with a weaker dependence on internal mixing. The switch of the mass-loss prescription based on the Eddington factor instead of the removal of outer layers, implies the existence of WNh stars with a large mass fraction of hydrogen at the surface () formed from initial masses of . These stars are constrained in a range of the HRD which corresponds to the MS band, in agreement with the observations of Galactic WNh stars at . While our models employ a fixed threshold for the switch to thick winds, rather than a continuous thin-to-thick wind model, the good reproduction of observations during the MS supports the robustness of the wind model upgrades, allowing its application to studies of late-stage stellar evolution before core collapse.

Accepted for publication in Astronomy & Astrophysics

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