Mass-loss predictions for O and B stars as a function of metallicity

We have calculated a grid of massive star wind models and mass-loss rates for a wide range of metal abundances between 1/100 and 10 Z/Zsun. The calculation of this grid completes the Vink et al. (2000) mass-loss recipe with an additional parameter Z. We have found that the exponent of the power law dependence of mass loss vs. metallicity is constant in the range between 1/30 and 3 Z/Zsun. The mass-loss rate scales as Mdot \propto Z^0.85 Vinf^p with p = -1.23 for stars with Teff \ga 25000 K, and p = -1.60 for the B supergiants with Teff \la 25000 K. Taking also into account the metallicity dependence of Vinf, using the power law dependence Vinf \propto Z^0.13 from Leitherer et al. (1992), the overall result of mass loss as a function of metallicity can be represented by Mdot \propto Z^0.69 for stars with Teff \ga 25000 K, and Mdot \propto Z^0.64 for B supergiants with Teff \la 25000 K. Our mass-loss predictions are successful in explaining the observed mass-loss rates for Galactic and Small Magellanic Cloud O-type stars, as well as in predicting the observed Galactic bi-stability jump. Hence, we believe that our predictions are reliable and suggest that our mass-loss recipe be used in future evolutionary calculations of massive stars at different metal abundance. A computer routine to calculate mass loss is publicly available.