Evolution of rotating massive stars adopting a newer, self-consistent wind prescription at SMC metallicity

Abstract

We use Geneva-evolution-code to run evolutionary tracks for stellar masses ranging from $20$ to $85$ $M_\odot$ at SMC metallicity ($Z=0.002$). We upgrade the recipe for stellar winds by adopting our self-consistent m-CAK prescription, which reduces the value of mass-loss rate by a factor between 2 and 6 depending on the mass range. The impact of our new winds is wide, and it can be divided between direct and indirect impact. For the most massive models ($60$ and $85$ $M_\odot$) with $\dot M\gtrsim2\times10^{-7}$ $M_\odot$ yr$^{-1}$, the impact is direct because lower mass loss make stars remove less envelope and therefore remain more massive and less chemically enriched at their surface at the end of their MS phase. For the less massive models ($20$ and $25$ $M_\odot$) with $\dot M\lesssim2\times10^{-8}$ $M_\odot$ yr$^{-1}$, the impact is indirect because lower mass loss make the stars keep high rotational velocities for a longer period of time, then extending the H-core burning lifetime and reaching the end of the MS with higher surface enrichment. Given that the conditions at the H-depletion change, the stars will lose more mass during their He-core burning stages anyways. For $M_\text{zams}=20$ to $40$ $M_\odot$, our models predict stars will evolve through the Hertzsprung gap, from O-type supergiants to BSG and finally RSG, with larger mass fractions of helium compared to old evolution models. New models also set down to $M_\text{zams}=85\,M_\odot$ the minimal initial mass required for a single star to become WR at metallicity $Z=0.002$. New values for $\dot M$ need to be complemented with upgrades in additional features such as convective core overshooting and distribution of rotational velocities, besides more detailed observations from projects such as XShootU, in order to provide a robust framework for the study of massive stars at low metallicity environments.