SIMBAD references

The optical long-term variability of a sample of 20 known quasars and 9 quasar candidates in a field around the globular cluster M3 is studied. A large number of Schmidt plates have been measured with a time-baseline of almost three decades. Several methods were applied to estimate the strengths and the timescales of variability. The percentage of quasars with detected variability is between 65% and 85%. There are indications of a significant long-term variability mode in the studied quasar sample.