H-ALPHA EMISSION AND INFRARED EXCESS IN BE STARS - PROBING THE CIRCUMSTELLAR DISC

We present near-simultaneous (within one week) high-resolution H alpha spectra and near-infrared photometry of 69 B and Be stars. We confirm that, for the Be stars, the infrared excess and H alpha emission are correlated, albeit with a rather large scatter. Given the near-simulta neity of our observations, this scatter probably is not related to int rinsic variability, but rather reflects a genuine star-to-star variati on in physical conditions. In order to derive information about the de nsity and velocity structure of Be star discs, we calculate theoretica l infrared excesses, H alpha equivalent widths and H alpha line profil es for two different models. We find that the model used by Poeckert a nd Marlborough (1978a) to fit the spectrum of gamma Cas, is not capabl e of reproducing the observed correlation between the infrared excess and the excess H alpha equivalent width, producing - for given infrare d excess - H alpha emission lines that are weaker than observed. The m odel of Waters (1986), used successfully to fit the infrared excess co ntinuum emission of Be stars, also fails, producing H alpha emission l ines that are too strong. We discuss these results in terms of the den sity structure of the wind.