Hubble Space Telescope Observations of the Seyfert Galaxy NGC 3783: Discovery of Variable C IV Absorption
Hutchings, John B.; Reichert, Gail A.; Mushotzky, Richard F.; Weymann, Ray J.; Crenshaw, D. Michael; Maran, Stephen P.; Carpenter, Kenneth G.; Smith, Andrew M.
Abstract
We have discovered variable absorption lines in HST spectra of the Seyfert 1 galaxy NGC 3783. C IV λλ1548.2, 1550.8 absorption is present in an FOS spectrum on 1992 July 27 and a GHRS spectrum on 1994 January 16 at a radial velocity of -450 km s^-1^ relative to the emission-line peak, but there is no evidence for absorption in a GHRS spectrum on 1993 February 5. A GHRS spectrum on 1993 February 21, obtained just 16 days after the spectrum with no detectable C IV absorption, shows strong N V λλ1238.8, 1242.8 absorption lines, also at a radial velocity of -450 km s^-1^. The observations place constraints on the two types of models for absorption-line variability: bulk motion into the line of sight, and variable ionization of gas already in the line of sight.