CMF models of hot star winds II. Reduction of O star wind mass-loss rates in global models

TL;DR

This paper presents global wind models for O stars that predict significantly lower mass-loss rates than previous estimates, aligning better with some observational diagnostics and challenging traditional assumptions.

Contribution

The study introduces a new approach to modeling O star winds using CMF radiative transfer, resulting in lower mass-loss rate predictions without free parameters, and compares these with observational data.

Findings

Predicted mass-loss rates are 2-5 times lower than traditional models.

Models agree with some observational diagnostics, suggesting revised mass-loss estimates.

Discrepancies with Hα-based estimates can be explained by clumping factors.

Abstract

We calculate global (unified) wind models of main-sequence, giant, and supergiant O stars from our Galaxy. The models are calculated by solving hydrodynamic, kinetic equilibrium (also known as NLTE) and comoving-frame (CMF) radiative transfer equations from the (nearly) hydrostatic photosphere to the supersonic wind. For given stellar parameters, our models predict the photosphere and wind structure and in particular the wind mass-loss rates without any free parameters. Our predicted mass-loss rates are by a factor of 2--5 lower than the commonly used predictions. A possible cause of the difference is abandoning of the Sobolev approximation for the calculation of the radiative force, because our models agree with predictions of CMF NLTE radiative transfer codes. Our predicted mass-loss rates agree nicely with the mass-loss rates derived from observed near-infrared and X-ray line profiles and are slightly lower than mass-loss rates derived from combined UV and H$\alpha$ diagnostics. The empirical mass-loss rate estimates corrected for clumping may therefore be reconciled with theoretical predictions in such a way that the average ratio between individual mass-loss rate estimates is not higher than about $ 1.6 $. On the other hand, our predictions are by factor of $ 4.7 $ lower than pure H$\alpha$ mass-loss rate estimates and can be reconciled with these values only assuming a microclumping factor of at least eight.