Abstract
The present work deals with opacities in observed line emission of early type stars, as a tool to infer physical properties of the emitting regions. With the emphasis put on Be stars, the observed spectrum are first analyzed by means the intensity/linewidth method (Kastner & Bhatia 1998, MNRAS, 298, 763). This is a semiempirical method that assume emission lines associated with a constant source function in a homogeneous medium, plane-parallel geometry and complete frequency redistribution in the scattering processes. It is appropriate for analyzing both astrophysical and laboratory plasmas, and allows us to derive optical thicknesses and associated quantities, such as escape probabilities and atomic level populations. Once these quantities are obtained through the intensity/linewidth semiempirical method, we intend to compare them with theoretical predictions from spectroscopic models. In this way, the statistical equilibrium equations are solved by assuming a collisional radiative steady state model. By adopting suitable atomic models and rate coefficients for the different atomic processes taking place in the considered plasma, we are able to obtain intensity lines and populations of the involved atomic levels, as well as departures from ideal conditions (local thermodynamical equilibrium and transparent medium). Comparison between observational data and theoretical predictions permits us to impose constraints on physical parameters describing astrophysical and laboratory plasma.
