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Session 78 - Seyfert Galaxies.
Display session, Friday, January 09
Exhibit Hall,
During the Astro-1 and Astro-2 missions, the Hopkins Ultraviolet Telescope (HUT) observed a total of 16 low-redshift active galactic nuclei (AGN) in the largely unexplored wavelength region shortward of 1200 ÅWith this limited number of objects, we can do crude, but interesting, statistics on the frequency of Lyman limits and warm absorbers, correlate the strength of O VI line emission with other emission lines and continuum bands, and correlate far-UV spectral properties with detailed morphology as observed with the Hubble Space Telescope.
The sensitivity and long mission lifetime of the Far Ultraviolet Spectroscopic Explorer (FUSE), scheduled for launch in the fall of 1998, will increase the number of AGN observable in the 900--1200 Å\ band by a factor of \sim5. Prime goals for FUSE observations are the shape of the far-UV continuum, the strengths of far-UV emission lines, and the prevalence of intrinsic absorption and Lyman limits. FUSE observations will resolve velocity structure in the O VI absorbing gas, and in any neutral hydrogen gas. Observations of Seyfert 2s (in addition to NGC 1068) will search for strong line emission in O VI, C III, and N III indicative of shock-heated gas. FUSE will also be sensitive to any molecular gas (visible as H_2 absorption) along the line of sight. In BAL QSOs, FUSE will be able to measure the absorption in the EUV transitions of high ionization ions such as Si XII.
Much of the AGN science with FUSE will be obtained collaterally from observations used to probe O VI absorption and the D/H ratio in the Galactic halo. ``Snapshot" observations of \sim2000 s of \sim75 AGN will yield spectra with 1 Å\ resolution at a S/N of \sim10. High S/N, R\sim30,000 observations will be obtained for \sim15 of the brightest targets. Deep integrations (\sim100,000 s) on some objects, required for precision D/H measurements, will provide opportunities for monitoring intrinsic variability since these will require 10--20 visits per target.
