BALMER LINE VARIATIONS IN THE RADIO-LOUD ACTIVE GALACTIC NUCLEUS PG-1512+370

We present spectroscopic observations of the quasar PG 1512+370, cover ing the H beta line spectral range and collected at moderate resolutio n (2-7 Angstrom FWHM) from 1988 to 1996. The observations show that th e blue wing of the H beta broad profile component has changed signific antly in flux and shape between 1988 and 1990 and between 1995 and 199 6. A displaced blue peak on the H beta profile, visible in 1988, but n ot in the 1990-1995 spectra, is revealed again in one of the spectra o btained in 1996. The blue peak (in both the 1988 and 1996 spectra) is centered at Delta v(r) approximate to 3000(-500)(+500) km s-1 from the rest frame defined by the narrow component of H beta, and the [O III] lambda lambda 4959, 5007 lines. We discuss several conflicting interp retations of the data. We find that the variability of the H beta blue wing is consistent with Balmer line emission from regions whose motio n is predominantly radial, if variations of the blue wing are a respon se to continuum changes. Alternatively, we note that observed H beta l ine profile variations are consistent with a variable line component a s in a ''binary black hole'' scenario. More frequent observations of H beta are needed to distinguish among these hypotheses.