Intrinsic absorption is a valuable tool for probing structures in active galactic nuclei (AGN). While absorption may in principle arise anywhere in the host galaxy, the most interesting absorbers are those that appear to be associated with the central engine. These ``warm absorbers" commonly appear in the X-ray spectra of AGN ([Turner et al. 1993]; [Nandra & Pounds 1994]), and they could be material in the broad-emission-line region (BELR) (e.g. [Netzer 1993]; [Reynolds & Fabian 1995]) or the X-ray heated wind which forms the reflecting region in type 2 AGN ([Krolik & Kriss 1995]), or an entirely new component. If X-ray warm absorbers are related to associated UV absorption systems ([Mathur et al. 1994]; [Mathur, Wilkes, & Elvis 1995]), then UV and X-ray observations together place powerful constraints on the ionization structure of the absorber. In the X-ray one can measure the column densities of highly ionized species (e.g. O VII and O VIII) while simultaneously observing lower ionization relatives in the UV (O VI, N V, and C IV). Objects with strong UV absorption lines and soft X-ray absorption are therefore good candidates for further tests of this hypothesis.
The Seyfert 1 galaxy NGC 3516 exhibits unusually strong, variable
UV absorption lines ([Ulrich & Boisson 1983]; [Voit, Shull, & Begelman 1987]; [Walter et al. 1990];
[Kolman et al. 1993]; [Koratkar et al. 1996]),
and has a variable X-ray spectrum characteristic of the warm absorber
phenomenon ([Halpern 1982]).
Observations obtained with Ginga ([Kolman et al. 1993]; [Nandra & Pounds 1994])
show a flat power law with energy index 
over the 2--18 keV range,
a highly ionized iron edge with a corresponding total column density of
,
and a cold fluorescent Fe K
line with EW = 377 eV.
To measure simultaneously the X-ray and UV absorption in NGC 3516 we coordinated ASCA observations with the flight of the Astro-2 space shuttle mission in March 1995. Far-ultraviolet spectra obtained with the Hopkins Ultraviolet Telescope (HUT) that allow us to measure the resonance doublets of O VI, N V, Si IV and C IV are discussed in a companion paper by Kriss et al. (1996)Kriss96a.