Simultaneous photometry and spectroscopy of the Be star 28 (ω) CMa -: II.: Line profile modelling

We analyse a series of high-resolution line pro files of He I 6678 in the periodic Be star 28 CMa. A simple zeroth-order approximation to the eigenfunctions is used to model the line profile variations in terms of non-radial pulsation. In addition, we use the best available theory for the eigenfunction in a rotating star. In all cases the calculated fits to the observed profiles are poor. We conclude that non-radial pulsation is almost certainly not responsible for the line profile variations in this star. In an attempt to understand the very large Line profile changes, but negligible light variation, we consider a 'patch' model. This consists of a circular area on the photosphere having the same temperature, but a different intrinsic line width. A simple model of this kind produces a good fit to the line profile variations and to the photometry. We conclude that modulation of the profile by a patch on, or close to, the photosphere may offer a plausible starting point for understanding the periodic variations in some Be stars.