HUBBLE SPACE TELESCOPE OBSERVATIONS OF THE SEYFERT GALAXY NGC 3783: DISCOVERY OF VARIABLE C Ⅳ ABSORPTION

摘要

We have discovered variable absorption lines in HST spectra of the Seyfert 1 galaxy NGC 3783. C Ⅳ λλ 1548.2, 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.