THE BETA-PICTORIS CIRCUMSTELLAR DISK .21. RESULTS FROM THE DECEMBER 1992 SPECTROSCOPIC CAMPAIGN

We present the results of an observational multisite and multiwaveleng th spectroscopic campaign performed in December 1992 on beta Pic to te st our Falling Evaporating Body scenario. The unprecedented sampling o btained enabled us to follow the beta Pic variations from the ground o ver an 11-day period, and from the ground and space over a 5-day perio d. The evolution in terms of velocity and the timescales for variabili ty are studied, and comparisons are made between various variable elem ents (Ca II, Mn II, Fe II, Al III and Al II). Very significant activit y occurred throughout the campaign. We confirm the existence of two ve locity regimes: low-velocity, slowly variable lines, and high-velocity , rapidly variable ones. It is shown that the higher the redshift, the smaller the variability timescale, the smaller the filling factors of the absorbing clouds, and the wider the lines. We detect for the firs t time the local effect of stellar rotation described by Beust & Lissa uer (1994), which enables us to infer the location of the projection o f the infalling absorbing cloud on the stellar surface. The variabilit y of Fe Ir appears to be correlated with that of Call. Conversely, Al III variability is not correlated with that of Ca II. The observed evo lution and characteristics of the high-velocity events appear to be we ll explained by the evaporation of one single body The evolution of th e low-velocity variable events cannot be reproduced by the evaporation of one single body, but rather by a family of bodies on adjacent orbi ts.