Long-term photometry of Be stars. III. Evidence for periodic outbursts of lambda ERI and photometric activity in HR2142

Stromgren differential uvby photometry of lambda Eri and HR2142 is analyzed. The data were taken during the time interval 1983-1994 in the framework of the Long-Term Photometry of Variables project at La Silla. lambda Eri exhibited four photometric events (probably associated with line emission episodes) that last several months and which were characterized by a common pattern of change in all passbands ( ~ +/- 10(-3) mag/day) along with an apparent decrease of the amplitude of the short-term variability and an increase of the stellar temperature. A search for periodicities reveals that these events fit a 486d recurrence time. On the other hand, HR2142 showed a relatively ``quiet" long-term photometric behaviour, the orbital period being detected only marginally in the photometric data set. In contrast, a 344d period optimally fits the data. We discuss the possibility of an internal ``clock" regulating the outburst activity of lambda Eri and show that the photometric variability of HR2142 can hardly be explained by its interacting binary nature. We also discuss an empirical relationship found between frac {partial c₁}{partial u} and v sini in a sample of 11 Be stars. Based on observations obtained at ESO, Chile