A search for rapid photometric variations in southern Be and Bn stars

Fifteen Be, 5 Bn, and 1 B stars were monitored during 10 nights in March–April 1988 by means of photoelectricubvy photometry. At least 80% of the Be stars were found variable. Tentative periods between 0.3 and 4.3 days were derived for 13 stars of our entire sample. In all cases the stars are bluest when brightest. Variations in B0-B5e stars are, in average, of larger amplitude than in B5-B9e stars. Bn stars show, in general, variations of smaller amplitude than Be stars. We discuss these results in terms of the current models on short-term photometric variability. In addition, from the observed period distribution we deduce the existence of intrinsically slow Be rotators. We propose the rotation of slightly displaced poles of a weak global dipolar magnetic field as responsable for the rapid periodic light variations.Based on observations obtained at the European Southern Observatory, La Silla, Chile.