The beta Pictoris circumstellar disk. XIII. Survey of the variable CA II lines.

Over 200 Ca II K and H spectra of Beta Pictoris taken between September 19, 1989 and December 19, 1990 are presented. Many new variable features are observed, at low and high redshifts, together with a few blueshifted ones. The time scales for the variations are shown to be strongly dependent on the redshift of the variable lines. A rate of events of about 200/yr is derived; it is also shown that in some cases the absorbing cloud covers less than 40 percent of the stellar surface. The observed variations are analyzed and compared to those observed in the UV. These observations make it possible to test the present scenario of evaporating infalling bodies, in terms of velocity of variable lines, occurrence of variable events, small time-scale variations, and size of the absorbing cloud. It is shown that the observed velocity range for the variable components may be explained by the present scenario, as well as the size of the absorbing clouds.