The empirical metallicity dependence of the mass-loss rate of O- and early B-type stars

Understand

[Abridged] We present a comprehensive study of the metallicity dependence of the mass-loss rates in stationary stellar winds of hot massive stars.

• Assuming a power-law dependence of mass loss on metallicity, Mdot \propto Z^{m}, and adopting a theoretical relation between the terminal velocity and metallicity, v_inf \propto Z^{0.13} (Leitherer et al.), we find m = 0.83 +/- 0.16 for non-clumped outflows from an analysis of the wind momentum luminosity relation (WLR) for stars more luminous than 10^{5.2} Lsun.
• Within the errors, this result agrees with the prediction of m = 0.69 +/- 0.10 from Vink et al.
• For the high luminosity stars we find the mass loss rates to be greater than the predictions, implying wind clumping factors in their line-forming regions of ~4.