Evolution of rotating massive stars adopting a newer, self-consistent wind prescription at SMC metallicity
arxiv(2024)
摘要
We use Geneva-evolution-code to run evolutionary tracks for stellar masses
ranging from 20 to 85 M_⊙ 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_⊙) with
Ṁ≳2×10^-7 M_⊙ 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_⊙) with Ṁ≲2×10^-8 M_⊙ 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_zams=20 to 40 M_⊙, 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_zams=85 M_⊙ the minimal
initial mass required for a single star to become WR at metallicity Z=0.002.
New values for Ṁ 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.
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