New predictions for radiation-driven, steady-state mass-loss and wind-momentum from hot, massive stars: II. A grid of O-type stars in the Galaxy and the Magellanic Clouds

Context. Reliable predictions of mass-loss rates are important for massive-star evolution computations. Aims. We aim to provide predictions for mass-loss rates and wind-momentum rates of O-type stars, while carefully studying the behaviour of these winds as functions of stellar parameters, such as luminosity and metallicity. Methods. We used newly developed steady-state models of radiation-driven winds to compute the global properties of a grid of O-stars. The self-consistent models were calculated by means of an iterative solution to the equation of motion using full non-local thermodynamic equilibrium radiative transfer in the co-moving frame to compute the radiative acceleration. In order to study winds in different galactic environments, the grid covers main-sequence stars, giants, and supergiants in the Galaxy and both Magellanic Clouds. Results. We find a strong dependence of mass-loss on both luminosity and metallicity. Mean values across the grid are (M) over dot similar to L-*(2.2) and (M) over dot Z(*)(0.95); however, we also find a somewhat stronger dependence on metallicity for lower luminosities. Similarly, the mass loss-luminosity relation is somewhat steeper for the Small Magellanic Cloud (SMC) than for the Galaxy. In addition, the computed rates are systematically lower (by a factor 2 and more) than those commonly used in stellar-evolution calculations. Overall, our results are in good agreement with observations in the Galaxy that properly account for wind-clumping, with empirical (M) over dot versus Z(*) scaling relations and with observations of O-dwarfs in the SMC. Conclusions. Our results provide simple fit relations for mass-loss rates and wind momenta of massive O-stars stars as functions of luminosity and metallicity, which are valid in the range T-eff = 28 000-45 000 K. Due to the systematically lower values for (M) over dot, our new models suggest that new rates might be needed in evolution simulations of massive stars.

Automated summary

Reliable predictions of mass-loss rates and wind-momentum rates of O-type stars were provided by using newly developed steady-state models. The results showed a strong dependence of mass-loss on both luminosity and metallicity. The computed rates were systematically lower than those commonly used in stellar-evolution calculations, suggesting a need for new rates in evolution simulations of massive stars.