Optical Variability of 16 Quasi Stellar Objects

The authors report long term broad band optical photometry of a sample of 16 QSOs, including three BL Lacertae objects. Using plates originally obtained for the Asiago Supernova Search, up to 20 years of observations are available. Through an analysis of the results and consideration of photometric errors, the authors concluded that 9 objects are variable, 6 not variable and 1 suspicious. Data of all variable objects have been searched for periodicity, using the Fourier analysis technique, but no definite evidence has been found.