PARSEC evolutionary tracks of massive stars up to $350 M_\odot$ at metallicities 0.0001$\leq Z \leq$0.04

TL;DR

This paper presents new stellar evolutionary tracks for massive stars up to 350 solar masses across a wide metallicity range, incorporating a recent mass-loss formalism that aligns with observed stellar limits and predicts metallicity effects.

Contribution

Introduces updated PARSEC models for massive stars with a novel mass-loss formalism that reproduces observed limits without ad hoc assumptions and covers a broad metallicity spectrum.

Findings

Models reproduce the Humphreys-Davidson limit without ad hoc mass-loss enhancement.

Mass-loss rates become less metallicity-dependent near the Eddington limit.

Humphreys-Davidson limit brightness increases at lower metallicity.

Abstract

We complement the PARSEC data base of stellar evolutionary tracks with new models of massive stars, from the pre-main sequence phase to the central carbon ignition. We consider a broad range of metallicities, 0.0001$\leq Z \leq$0.04 and initial masses up to $M_{\rm ini}=350\,M_\odot$. The main difference with respect to our previous models of massive stars is the adoption of a recent formalism accounting for the mass-loss enhancement when the ratio of the stellar to the Eddington luminosity, $\Gamma_e$, approaches unity. With this new formalism, the models are able to reproduce the Humphreys-Davidson limit observed in the Galactic and Large Magellanic Cloud colour-magnitude diagrams, without an ad hoc mass-loss enhancement. We also follow the predictions of recent wind models indicating that the metallicity dependence of the mass-loss rates becomes shallower when $\Gamma_e$ approaches unity. We thus find that the more massive stars may suffer from substantial mass-loss even at low metallicity. We also predict that the Humphreys-Davidson limit should become brighter at decreasing metallicity. We supplement the evolutionary tracks with new tables of theoretical bolometric corrections, useful to compare tracks and isochrones with the observations. For this purpose, we homogenize existing stellar atmosphere libraries of hot and cool stars (PoWR, ATLAS9 and Phoenix) and we add, where needed, new atmosphere models computed with WM-basic. The mass, age and metallicity grids are fully adequate to perform detailed investigations of the properties of very young stellar systems, both in local and distant galaxies. The new tracks supersede the previous old Padova models of massive stars.