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

Context. Massive stars are characterised by powerful stellar winds driven by radiation; thus, the mass-loss rate is known to play a crucial role in their evolution.Aims. We study the evolution of two massive stars (a classical massive star and a very massive star) at solar metallicity (Z = 0.014) in detail. We calculate their final masses, radial expansion, and chemical enrichment, at their H-core, He-core, and C-core burning stages, prior to their final collapse.Methods. We ran evolutionary models for initial masses of 60 and 200 M_{⊙ using MESA and the Geneva-evolution-code (GENEC). For the mass loss, we adopted 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 luminous Wolf-Rayet (WR) stars of the nitrogen sequence with hydrogen in their spectra (WNh stars), and a hydrodynamically consistent formula for the H-poor thick wind of classical WR stars. The transition from thin to thick winds was set to Γe = 0.5.Results. The unification of the initial set-up for the stellar structure and wind prescription leads to very similar black hole mass for both GENEC and MESA codes, but both codes predict different tracks across the Hertzsprung-Russell diagram (HRD) For the 60 M⊙ case, the GENEC model predicts a more efficient rotational mixing and more chemically homogeneous evolution, whereas the MESA model predicts a large radial expansion that reaches the Luminous Blue Variable (LBV) phase. For the 200 M⊙ 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.Conclusions. 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 (Xsurf ≥ 0.3) formed from initial masses of ≳60 M⊙. These stars are constrained in a Teff range of the HRD which corresponds to the main sequence band, in agreement with the observations of Galactic WNh stars at Z = 0.014. While our models employ a fixed Γe, trans threshold for the switch to thick winds, rather than a continuous thin-to-thick wind model, the good reproduction of observations during the main sequence supports the robustness of the wind model upgrades, allowing its application to studies of late-stage stellar evolution before core collapse.}