1998A&A...335..565H

The high accuracy and the homogeneity of Hipparcos data for bright stars have allowed us to quantify the degree of variability of Be stars. This degree has been found to be highly dependent on the temperature of the star. Rapid variability is the main feature of the 86% of early Be and less than 20% of late Be stars taking into account the limit of detection considered. In addition to Be stars reported in the Hipparcos catalogue (ESA, 1997HIP...C......0E) as short-period variables, we have been able to enlarge the number of detections as well as to confirm periods previously determined. Be stars that show larger amplitude rapid variations are proposed as candidates for a search of multiperiodicity i.e. as non-radial pulsators. We have also searched for the presence of outbursts and fading events in the Hipparcos data. Outbursts have been frequently and preferentially detected in early Be stars with rather low to moderate vsini while fading events seem to be more conspicuous in stars with higher v sini. Mid-term and long-term variations have also been investigated. Several stars have shown some evidence of temporary quasi-periodic oscillations ranging between 10 and 200 days. Finally information concerning long-term variations is reported. Cycles shorter than or equal to the Hipparcos mission have mainly been detected in stars earlier than B6. Long-term time scales of late Be stars are confirmed to be longer by far.