Profiles of emission lines contain key information on the dynamics, the physical condition, and the geometry of the cool envelopes of Be stars. Despite much observational evidence, doubts persist about the rotating, equatorial ring model first proposed by Struve (1931) to explain the gross features of the profiles and later developed by Huang (1972) in the two-dimensional, transparent limit. The basic rotating model is now reconsidered and profile formation studied from a physical point of view.

The excitation structure of a disk rotating around a B star in circular, Keplerian orbits is computed by means of a new, iterative approach. The approach takes full account of both stellar and diffuse radiation at line and continuum frequencies and makes no assumptions about the optical properties of the disk. It is applied to an isothermal model with parameters based on observations of the shell star 48 Librae.