9926(  1) - 04/04/03 10:20  - [  1]

    PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS   ST ScI Use Only
                                                       ID:      9926
                                                       Version: 1
                                                       Check-in Date: 04-Apr-2003
                                                                      10:19:44

1.Proposal Title:
A Detailed Photoionization Study of the Broad Line Region of NGC 5548
------------------------------------------------------------------------------------
2. Proposal For  3. Cycle
AR               11
------------------------------------------------------------------------------------
4. Investigators
                                                                                     Contact?
    PI: C. Gaskell                        University of Nebraska - Lincoln
   CoI: Ms. Stephanie Snedden             New Mexico State University                   N

------------------------------------------------------------------------------------
5. Abstract

NGC 5548 probably has the best-studied broad line region (BLR) of any AGN. It
therefore provides an excellent laboratory for investigating many fundamental BLR
questions. We propose to use the large set of HST NGC 5548 spectra taken in 1993 to
(a) test photoionization analyzes of BLR clouds, (b) attempt to unravel the various
emission line components, and (c) understand how the BLR gas is moving. This data
set is uniquely suited to this because of the excellent sampling, high signal-to-
noise ratio and large sample of contemporaneous optical spectra available. Because
we know the distribution of the BLR gas in NGC 5548 better than in any other AGN and
because the multi-wavelength variability history is known, many major uncertainties
in previous BLR studies are greatly reduced. We will be using Gary Ferland's
photoionization code ``CLOUDY'' to derive physical conditions as a function of both
projected velocity and time. The key ingredient in our proposed study is requiring
consistency in derived conditions as NGC 5548 varied in continuum and line strength
by almost a factor of two during the 1993 monitoring. From this we hope to be able
to separate out the various kinematic components and understand the gas motions. We
are particularly interested in evaluating disk and disk-plus-wind models
------------------------------------------------------------------------------------
                                                9926(  1) - 04/04/03 10:20  - [  2]

            Summary Form for Proposal  9926

  Item                         Used in this proposal
------------------------------------------------------------------------------------------------------------------------------------
  Proposal Category            AR
------------------------------------------------------------------------------------------------------------------------------------