NLTE models of line-driven stellar winds^*

I. Method of calculation and first results for O stars

¹ Ústav teoretické fyziky a astrofyziky PřF MU, 611 37 Brno, Czech Republic
² Department of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, UK
³ Astronomický ústav, Akademie věd České republiky, 251 65 Ondřejov, Czech Republic

Corresponding author: J. Krtička, krticka@physics.muni.cz

Received: 1 July 2003
Accepted: 24 November 2003

Abstract

New numerical models of line-driven stellar winds of late O stars are presented. Statistical equilibrium (NLTE) equations of the most abundant elements are solved. Properly obtained occupation numbers are used to calculate consistent radiative force and radiative heating terms. Wind density, velocity and temperature are calculated as a solution of model hydrodynamical equations. Contrary to other published models we account for a multicomponent wind nature and do not simplify the calculation of the radiative force (e.g. using force multipliers). We discuss the convergence behaviour of our models. The ability of our models to predict correct values of mass-loss rates and terminal velocities of selected late O stars (mainly giants and supergiants) is demonstrated. The systematic difference between predicted and observed terminal velocities reported in the literature has been removed. Moreover, we found good agreement between the theoretical wind momentum-luminosity relationship and the observed one for Cyg OB2 supergiants.