Absolute magnitudes of B emission line stars : correlation between the luminosity excess and the effective temperature.

A new determination of the visual absolute magnitude of Be stars is carried out. For this, a new calibration of visual absolute magnitudes of B stars of luminosity classes, V, IV, and III is first obtained from a sample of 215 stars. The absolute luminosity excess in the visual is determined for a sample of 49 Be stars. It is found that this excess is correlated with the effective temperature of the underlying stars. A well defined correlation between this excess and the emission in the first two Balmer lines is established. From these results, using a simple model of circumstellar envelope, it is inferred that the zones of the circumstellar envelope contributing to the emission in the continuum and in the lines have to be rather small. It is also deduced that the emission measure of the envelope is correlated with the temperature of the central star and that the irregular photometric variations of Be stars are an envelope-opacity phenomenon.