Self-consistent coupling of radiative transfer and dynamics in dust-driven winds

Abstract

Models of stationary dust-driven winds of late-type stars are investigated. The flow is described succes- sively using three models which couple, in spherical symmetry, the grain-gas dynamics in a self-consistent way with radiative transfer. 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. The rst model is used to check one classical hypothesis, that where the gas and the grains expand at the same velocity, the flow is described by a one-fluid model. This model is then improved in a second model, to include complete momentum coupling between gas and grains by friction. Finally, a third model includes grains and gas coupled by friction as well as the eects of inertial force on grains. By means of a numerical iteration, dynamics and radiative transfer are coupled in order 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 be important for wind models which are all highly sensitive to input data. In conclusion, approximations (position and momentum coupling) for the dynamics should be relaxed.