Optical variability of the medium-bright quasar sample

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Abstract

We report on a variability study of the 32 member Medium-Bright Quasar Sample (MBQS) which is complete to nominal limiting magnitudes up to B = 17.6. The study was conducted with the help of a uniform series of blue-sensitive filtered plates, taken with the Palomar 1.2 m Schmidt telescope spanning the years 1978-1981. The variability of the quasars is tested with the help of a control group of hot stars. Variability is characterized by a canonical standard deviation for each time series and an extremum statistic Q. Primary calibration is achieved with the help of photometric standards kindly supplied by A. Sandage. A method of secondary calibration is devised to counter epoch-dependent differences and large-scale irregularities in plates, and succeeds in reducing dispersions. We find that the star US 1953 has undergone a noticeable variation in the course of 26 hr. Apparent variations in the extragalactic object US 3498 may be illusory, owing to its partially resolved appearance. No other evidence for variability was detected. The longer term variability properties were examined with the help of the Palomar Observatory Sky Survey and are briefly discussed.

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