CMF models of hot star winds
I. Test of the Sobolev approximation in the case of pure line transitions

Jiri Krticka, Jiri Kubat

Masaryk University, Brno, Czech Republic
Astronomical Institute, Ondrejov, Czech Republic

We provide hot star wind models with radiative force calculated using
the solution of comoving frame (CMF) radiative transfer equation. The wind
models are calculated for first stars, O stars, and central stars of planetary
nebulae. We show that without line overlaps and with solely thermal line
broadening the pure Sobolev approximation gives reliable estimate of the
radiative force even close to the wind sonic point. Consequently, models with
the Sobolev line force provide good approximation for solutions obtained with
non-Sobolev transfer. Taking line overlaps into account, the radiative force
becomes slightly lower, which leads to the decrease of the wind mass-loss rate
by roughly 40%. Below the sonic point the CMF line force is significantly lower
than the Sobolev one. In the case of pure thermal broadening this does not
influence the mass-loss rate, as the wind mass-loss rate is set in the
supersonic part of the wind. However, when additional line broadening is present
(e.g., the turbulent one) the region of low CMF line force may extend outwards
to the regions where the mass-loss rate is set. This results in decrease of the
wind mass-loss rate. This effect can at least partly explain low wind mass-loss
rates derived from some observational analyses of luminous O stars.

Reference: Astronomy and Astrophysics, in press
Status: Manuscript has been accepted