THE ENSEMBLE VARIABILITY PROPERTIES OF FAINT QSOS

A refined sample of 64 variable objects with stellar image structure h as been identified in SA 57 to B approximately 22.5, over a time basel ine of 15 yr, sampled at 11 distinct epochs. The photometric data typi cally have a root-mean-square error at B = 22 of only 0.05 mag. Thirty -five quasars in this field have already been spectroscopically confir med, 34 of which are among the sample of variables. Of the other varia bles, six are known spectroscopically to be stars, 10 additional objec ts are stars based on reliable detection of proper motion, and one is spectroscopically a narrow emission line galaxy. Of the 13 remaining v ariables, it is argued that they are a mixture of distant halo subdwar fs and quasars with starlike colors. We compute the ensemble average s tructure function and autocorrelation function from the light curves i n the respective quasar rest frames, which are used to investigate the general dependences on apparent magnitude, absolute magnitude, and re dshift.