STIS Echelle Observations of the Intrinsic UV Absorption in the Seyfert 1 Galaxy NGC 3783

We present observations of the UV absorption lines in the Seyfert 1 galaxyNGC 3783, obtained with the medium resolution echelle gratings of the SpaceTelescope Imaging Spectrograph(STIS) on the Hubble Space Telescope (HST). Thespectra reveal the presence of three kinematic components of absorption inLy-alpha, C IV, and N V, at radial velocities of -1365, -548, and -724 km/swith respect to the systemic velocity of the host galaxy (Components 1, 2 and3, respectively); Component 1 also shows absorption by Si IV. Component 3 wasnot detected in any of the earlier Goddard High Resolution Spectrograph (GHRS)spectra, and the C IV absorption in the other components has changed since themost recent GHRS observation obtained 5 yr earlier. Somewhat unexpectedly, eachcomponent has a covering factor (of the continuum source + broad emission lineregion) of about 0.6. We have calculated photoionization models to match the UVcolumn densities in each of the three components. Based on the model results,there should be strong absorption in the bandpass of the Far UltravioletSpectroscopic Explorer (FUSE), 912 - 1200 A, including saturated O VI lines ateach component velocity. The models also predict large O VII and O VIII columndensities but suggest that the UV absorbers cannot account for all of the X-rayabsorption detected in recent Chandra spectra. Finally, there is no evidencefor a correlation between the characteristics of the UV absorbers and the UVcontinuum flux, which suggests that the variations observed in the GHRS andSTIS spectra are due in large part to changes in the column densities of theabsorbers as the result of transverse motion.Comment: 29 pages, Latex, includes 3 figures (encaps. postscript), four additional tables in Latex landscape format, to appear in the Astrophysical Journa