Intensive Spectroscopic Monitoring of NGC 5548 with HST, IUE, and Ground-Based Telescopes

We present the results of a combined HST/IUE/ground-based spectroscopic monitoring campaign on the Seyfert 1 galaxy NGC 5548 that was undertaken in order to address questions that require both high temporal resolution (one day) and high signal-to-noise ratios. We find (1) that the ultraviolet and optical continuum variations are virtually simultaneous, (2) that the Heii lambda1640 emission-line variations lag behind the continuum variations by somewhat less than 2 days, and (3) the velocity field of the Civ-emitting region is not dominated by radial motion, although we find some indication that the emission-line wings (| Delta v right | >= 3000kms(-1) ) respond to continuum variations slightly more rapidly than does the core, which is qualitatively what is expected for a virialized cloud system. We are pleased to acknowledge support of the space-based component of this project by NASA through grants NAG5-1824 and STScI grant GO-3484.01-91A. Support for the ground-based observations by NSF through several grants (including AST-9112870 to OSU) is also gratefully acknowledged.