THEORY AND SELF-CONSISTENT MODEL OF DUST-DRIVEN WINDS

Abstract

The aim is to determine the role and the influence of assumptions concerning both dynamics and radiative transfer in models of winds and mass loss of evolved stars, when the radiative force on dust grains plays a major role in the structuration of the circumstellar envelope of the star. The flow is described successively using three models coupling the grain and the gas dynamics in a self-consistent way with radiative transfer for three different approaches of the dynamics: the Position Coupling, the Momentum Coupling and the Full Problem. A complete radiative transfer including multiple scattering, absorption and thermal emission is taken into account to determine the temperature of dust grains which in turn governs their thermal emission. The medium is not necessarily optically thin. In all cases, numerical iterations couple dynamics with transfer. Thus two codes are used alternately, starting with an initial profile of radiation pressure, until convergence to a self-consistent solution. This emphasizes the importance of the drift velocity between the grains and the gas, and the inertia of dust together with hydrodynamics/transfer coupling. When the medium is optically thick, an opaque zone is located at the base of the wind. This zone governs the whole envelope structure. Finally, the exact number of solutions was determined for the one-fluid model.