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We present the results of the study of visible (BVRI) intra-night variability of the BL Lac object OJ287. The observations were carried out on a total of 29 nights during the period November 1993-October 1994, with only nights with at least 4 observations being included. Three telescopes were used for the study: the 1m Jacobus Kapteyn Telescope and the 2.56m Nordic Optical Telescope at El Roque de los Muchachos Observatory (La Palma) and the 82cm IAC-80 Telescope at Teide Observatory (Tenerife). Most of the data were taken in Johnson V. Relative CCD photometry was carried out against Star 10 of the standard sequence. Microvariability is frequently, but not always detected, even on the nights with the lowest errors; globally, only 41% of nights show clear variability.
Given a detection criterion of >95% probability of reality, only 4 of 10 nights in which our detection threshold was 5% amplitude in flux or less (40%) showed variability; 19% of nights with threshold 5-10% also showed microvariability, but on only 1 night (3%) was variability greater than 10% found; some nights may also show isolated variations which would not show up in our statistics.
There is evidence of correlation between variability amplitude and the brightness of OJ287, with greater amplitude of variation being seen at brighter magnitudes. The much smaller quantities of data taken in B, R and I do not allow us to come to a clear conclusion yet about the possibility of a correlation between the frequency and the amplitude of variability, which would permit us to diferentiate between different models for generating the microvariability.
