2021A&A...648A..36B

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 dM/dt∼L_*^2.2 and dM/dt∼L_*^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 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=28000-45000K. Due to the systematically lower values for M, our new models suggest that new rates might be needed in evolution simulations of massive stars.