Expanding atmospheric model including a chromosphere. I: Study of the infrared excess in Be stars

By means of a rigorous solution of the radiative transfer equation for a spherically symmetric medium, we studied the contribution of a stellar wind and a chromospheric structure to the IR continuum of Be stars. We made a detailed analysis of the different continuum opacity sources that contribute to the emergent flux. For different wavelengths (from UV to far-IR) we determined the continuum formation region, its inner and outer radii, and its relation to the chromospheric region. Since H free-free emission turns out to be the main emission mechanism, this model may explain the continuum spectrum of some Be stars, i.e., the stars classified in category F (according to Allen's 1973 classification)