SPECTRAL MONITORING OF POWERFUL RADIO-SOURCES

High-resolution (approximately 1.5 angstrom) optical spectra of the wave-length range around H-beta lambda-4861 have been obtained for four quasars (PKS 0736 + 017, 4C 31.45, 3C 263 and 3C 273) and one Seyfert 1 galaxy (3C 120). For three sources, 3C 120, PKS 0736 + 017 and 3C 273, two or more spectra were made at time intervals of 1-1.5 yr. There is evidence for a mild variability of the broad H-beta line in all three objects; this is most marked in the case of 3C 120. Light travel time arguments then infer the dimensions of the BLR to be of the order of a lightyear or less, assuming the BLR clouds to be spherically distributed.