A New Prescription for the Mass-loss Rates of WC and WO Stars

Tramper, F.; Sana, H.; de Koter, A.

The Astrophysical Journal, Volume 833, Issue 2, 133 (2016)

ADS – Journal – arXiv

Abstract

We present a new empirical prescription for the mass-loss rates of carbon- and oxygen-sequence Wolf-Rayet stars as a function of their luminosity, surface chemical composition, and initial metallicity. The new prescription is based on results of detailed spectral analyses of WC and WO stars and improves the often applied Nugis and Lamers relation. We find that the mass-loss rates of WC and WO stars (with X = 0 and Y ≲ 0.98) can be expressed as {log} \dot{M}=-9.20+0.85{log}(L/L ) + 0.44 log Y + 0.25 log (Z Fe/Z Fe,☉). This relation is based on mass-loss determinations that assume a volume-filling factor of 0.1, but the prescription can easily be scaled to account for other volume-filling factors. The residual of the fit is σ = 0.06 dex. We investigated whether the relation can also describe the mass loss of hydrogen-free WN stars and showed that it can when an adjustment of the metallicity dependence ({log} \dot{M}\propto 1.3{log}({Z}{Fe}/{Z}{Fe,☉ })) is applied. Compared to that of Nugis and Lamers, \dot{M} is less sensitive to the luminosity and the surface abundance, implying a stronger mass loss of massive stars in their late stages of evolution. The modest metallicity dependence implies that if WC or WO stars are formed in metal-deficient environments, their mass-loss rates are higher than currently anticipated. These effects may result in the formation of a larger number of SNe Ic and fewer black holes and may favor the production of superluminous SNe Ic through interaction with C- and O-rich circumstellar material or dense stellar wind.

Keywords: stars: evolution; stars: fundamental parameters; stars: mass-loss; stars: massive; stars: winds; outflows; stars: Wolf─Rayet; Astrophysics – Solar and Stellar Astrophysics


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