Diagnosis of stellar winds and temperature structures in Be stars through the analysis of Mg II lines

Abstract

We compute non-LTE Mg II line profiles for Be stars by considering 12 energy-level atoms and supposing that the circumstellar medium can be described by an expanding, spherically symmetric flow in which we assume the presence of a chromosphere. The line radiative transfer equation was solved rigorously in spherical coordinates and in the comoving frame. The Mg II line profiles predicted by this model coincide with those observed in some Be stars. The calculation was performed for a range of effective temperatures representative of the B spectral type. We have also analyzed the influence on the line profiles of different temperature and velocity distributions in the circumstellar material. The line spectrum variability of a Be star is interpreted as the result of a variable outward mass flux.