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

摘要

We provide hot star wind models with radiative force calculated usingthe solution of comoving frame (CMF) radiative transfer equation. Thewind models are calculated for the first stars, Ostars, andthe central stars of planetary nebulae. We show that without lineoverlaps and with solely thermal line broadening the pure Sobolevapproximation provides a reliable estimate of the radiative force evenclose to the wind sonic point. Consequently, models with the Sobolevline force provide good approximations to solutions obtained withnon-Sobolev transfer. Taking line overlaps into account,theradiative force becomes slightly lower, leading to adecrease in the wind mass-loss rate by roughly40%. Below thesonic point, the CMFline force is significantly lowerthan the Sobolev one. Inthe case of pure thermal broadening,this does not influence the mass-loss rate, asthe windmass-loss rate is set in the supersonic part of the wind. However, whenadditional line broadening is present (e.g.,the turbulentone) the region of low CMF line force may extend outwards to theregions where the mass-loss rate isset. This results in adecrease in the wind mass-loss rate. This effect can at least partlyexplain the low wind mass-loss rates derived from some observationalanalyses of luminous Ostars.Key words: stars: winds, outflows - stars:mass-loss - stars: early-type - hydrodynamics - radiative transfer