Self-consistent coupling of radiative transfer and dynamics in dust-drivenwinds

Models of stationary dust-driven winds of late-type stars are investigated. The ow is described successively using three models which couple, in spher ical symmetry, the grain-gas dynamics in a self-consistent way with radiati ve transfer. Complete radiative transfer including multiple scattering, abs orption and thermal emission is taken into account to determine the tempera ture of dust grains which in turn governs their thermal emission. The mediu m is not necessarily optically thin. The first model is used to check one c lassical hypothesis, that where the gas and the grains expand at the same v elocity, the ow is described by a one-fluid model. This model is then impro ved in a second model, to include complete momentum coupling between gas an d grains by friction. Finally, a third model includes grains and gas couple d by friction as well as the effects of inertial force on grains. By means of a numerical iteration, dynamics and radiative transfer are coupled in or der to achieve a self-consistent solution in all cases. Even for fairly low non-zero optical depths, coupling of radiation with dynamics is found to b e important for wind models which are all highly sensitive to input data. I n conclusion, approximations (position and momentum coupling) for the dynam ics should be relaxed.