HOW FAST DO QUASAR EMISSION-LINES VARY - FIRST RESULTS FROM A PROGRAMTO MONITOR THE BALMER LINES OF THE PALOMAR-GREEN QUASARS

We have monitored spectrophotometrically a subsample (28) of the Palom ar-Green Bright Quasar Sample for 2 years in order to test for correla tions between continuum and emission-line variations and to determine the timescales relevant to mapping the broad-line regions of high-lumi nosity AGNs. Half of the quasars showed optical continuum variations w ith amplitudes in the range 20-75%. The rise and fall time for the con tinuum variations is typically 0.5-2 years. In most of the objects wit h continuum variations, we detect correlated variations in the broad H alpha and H beta emission lines. The amplitude of the line variations is usually 2-4 times smaller than the optical continuum fluctuations. We present light curves and analyze spectra for six of the variable q uasars with 1000-10,000 Angstrom luminosity in the range of 0.3-4 x 10 (45) ergs s(-1). In four of these objects the lines respond to the con tinuum variations with a lag that is smaller than or comparable to our typical sampling interval (a few months). Although continued monitori ng is required to confirm these results and increase their accuracy, t he present evidence indicates that quasars with the above luminosities have broad-line regions smaller than about 1 lt-yr. Two of the quasar s monitored show no detectable line variations despite relatively larg e-amplitude continuum changes. This could be a stronger manifestation of the low-amplitude line-response phenomenon we observe in the other quasars.