NLTE models of line-driven stellar winds I. Method of calculation and first results for O stars

TL;DR

This paper introduces a new method for modeling line-driven stellar winds in late O stars, solving NLTE equations and accounting for multicomponent wind effects, resulting in improved predictions of wind properties.

Contribution

The paper presents a novel calculation approach that explicitly models multicomponent winds and avoids simplifying assumptions like force multipliers, enhancing accuracy in wind predictions.

Findings

Accurately predicts mass-loss rates and terminal velocities for late O stars.

Removes systematic discrepancies between predicted and observed terminal velocities.

Shows good agreement with observed wind momentum-luminosity relationships.

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.