TIME SCALES OF LONG-TERM OPTICAL BASE-LEVEL FLUCTUATIONS IN 3 CLASSESOF AGN

The long-term optical light curves of many active galactic nuclei (AGN ) display smooth, cyclic changes in level on time scales of years. Ear lier work by Smith et al. (AJ, 105, 437, 1993) estimated the time scal es of this previously undiscussed phenomenon for a sample of 60 classi cal radio-loud quasars. The present study extends the analysis to thre e additional groups of AGN: the BL Lacertids, the compact galaxies, an d the radio-quiet quasars. The average time scale of the BL Lacertids is approximately equal to that of the classical quasars, lending crede nce to unified models of these objects. The long-term fluctuations of the compact galaxies and the radio-quiet quasars are slower. Our analy sis tends to support the division of the BL Lacertids into two populat ions.