Stellar evolution with rotation XI: Wolf-Rayet star populations at different metallicities

TL;DR

This study models massive star evolution with rotation across different metallicities, showing rotation's significant impact on Wolf-Rayet star formation, lifetimes, and supernova type ratios, aligning well with observations.

Contribution

It introduces comprehensive rotating stellar models at various metallicities, improving predictions of Wolf-Rayet star populations and supernova ratios compared to non-rotating models.

Findings

Rotating models predict earlier entry into the WR phase.

Rotation increases WR lifetimes, especially in the eWNL phase.

Models match observed supernova type ratios across metallicities.

Abstract

Grids of models of massive stars ($M \ge$ 20 $M_\odot$) with rotation are computed for metallicities $Z$ ranging from that of the Small Magellanic Cloud (SMC) to that of the Galactic Centre. The hydrostatic effects of rotation, the rotational mixing and the enhancements of the mass loss rates by rotation are included. The evolution of the surface rotational velocities of the most massive O--stars mainly depends on the mass loss rates and thus on the initial $Z$ value. The minimum initial mass for a star for entering the Wolf--Rayet (WR) phase is lowered by rotation. For all metallicities, rotating stars enter the WR phase at an earlier stage of evolution and the WR lifetimes are increased, mainly as a result of the increased duration of the eWNL phase. Models of WR stars predict in general rather low rotation velocities ($ < 50$ km s$^{-1}$) with a few possible exceptions, particularly at metallicities lower than solar where WR star models have in general faster rotation and more chance to reach the break--up limit.The properties of the WR populations as predicted by the rotating models are in general in much better agreement with the observations in nearby galaxies. The observed variation with metallicity of the fractions of type Ib/Ic supernovae with respect to type II supernovae as found by Prantzos & Boissier (\cite{Pr03}) is very well reproduced by the rotating models, while non--rotating models predict much too low ratios.