AN HISTORICAL LIGHT-CURVE OF ON-231 AND ITS PERIODIC ANALYSIS

All data in the B band for BL Lac object ON 231 have been compiled int o a light curve from twenty-six publications, dating back to 1892; 560 values are available. The light curve shows that ON 231 is very activ e and exhibits very complicated non-sinusoidal variations. The light c urve probably consists of three kinds of behaviours. The first may be nonperiodic or with a period at least longer than the duration of hist orical observations. In this case, the source seems to maintain two st ates of intensities, changing in mean behaviour from a bright level wi th about mean B magnitude 15.45 to a faint level with about 16.45 mag between 1969 and 1972. After detailed Jurkevich V-m(2) test analysis, we found that the second is periodic, with a period of 13.6 +/- 1.3 ye ars (or 26.6 +/- 0.8 years) with outburst structure of one magnitude w ith total width of about 6 years. The third one is sporadic, superposi ng on the previous two behaviors. the periods of 0.981 +/- 0.005 years (or 2.02, 3.01,... years) and of a few days are not significant and m ay be spurious.