The Metallicity Dependence of Wolf-Rayet Mass Loss

TL;DR

This study models Wolf-Rayet star winds across different metallicities, revealing how mass-loss rates depend on metallicity and self-enrichment effects, with implications for stellar evolution in low-metallicity environments.

Contribution

It provides a detailed analytic model of Wolf-Rayet star mass loss as a function of metallicity, highlighting the metallicity thresholds for wind existence and the effects of self-enrichment.

Findings

Mass-loss rate scales as Z^{0.5} for Z >= 0.01 Z_sun.

Winds cease below Z ~ 0.001 Z_sun for WN stars.

Self-enrichment causes flattening of mass-loss rates at very low metallicity.

Abstract

We produce models of early WN, WC, and WO stars as a function of metallicity Z using an analytic CAK-type approach. At log(Z / Z_sun) >= -2 both WN and WC stars have the approximate dependence Mdot \propto Z^{0.5}. For a WN wind the mass-loss rate drops rapidly below log(Z / Z_sun) = -2, and no wind solution can be found for log(Z / Z_sun) < -3. For WC and WO winds the mass-loss rate plummets in the range -3 <= log(Z / Z_sun) <= -2 and tends to flatten due to the self-enrichment of C and O to around 10^{-8} M_sun yr^{-1} for log(Z / Z_sun) <= -4. No significant difference in Mdot was found for WC versus WO stars at low metallicity.