Resonance line transfer and transport of excited atoms—II. Self-consistent solutions (1)

Abstract

This second part of our study of non-LTE line transfer with convective transport of excited atoms presents self-consistent solutions of the radiative transfer equation and the kinetic equation of the excited two-level atoms, for the limiting case of no elastic velocity-changing collisions of the excited atoms. Pure Doppler broadening of the spectral line is assumed. We investigate reflecting and destroying boundaries for the excited atoms, while the boundary condition for the photons corresponds to free photon escape from the system. Our numerical procedure for solving the two coupled kinetic equations for the excited atoms and the photons is an iterative method using variable Eddington factors, and is described in detail. We present a simple model that considers the gas of excited atoms and the radiation field as two interacting fluids, which yields a straightforward interpretation of the various scale lengths encountered in the numerical results for the hydrodynamic properties (density, flux density, mean velocity) of the gas of excited atoms.