ORFEUS-II FAR-ULTRAVIOLET OBSERVATIONS OF 3C273 - THE INTRINSIC SPECTRUM

Using the Berkeley spectrometer of the ORFEUS-SPAS II mission, we obse rved the spectrum of the blight, low-redshift QSO 3C 273 in the wavele ngth range 900-1200 Angstrom (780-1040 Angstrom in the QSO's rest fram e). The QSO's spectrum is dominated by broad emission blends of the re sonance lines of O VI, C III, N III, and S VI. Only relatively weak em ission is detected at the wavelengths of the higher Lyman lines, and n o significant Lyman discontinuity is present at the QSO's redshift. Th e reddening-corrected underlying smooth continuum shows (for the epoch of the ORFEUS observations) a turnover of the nu F-nu spectrum at abo ut 2.5 x 10(15) Hz. While this turnover frequency is in the general ra nge expected for active galactic nucleus accretion disks, it is lower than predicted for QSOs as luminous as 3C 273 by standard accretion di sk models.