7996(  1) - 04/16/98 14:12  - [  1]

    PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS   ST ScI Use Only
                                                       ID:      7996
                                                       Version: 1
                                                       Check-in Date: 16-Apr-1998
                                                                      14:09:07

1.Proposal Title:
The Abundance of Interstellar Sulfur
------------------------------------------------------------------------------------
2. Proposal For  3. Cycle
AR               7
------------------------------------------------------------------------------------
4. Investigators
                                                                                     Contact?
    PI: David M. Meyer                    Northwestern University

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

Observations of interstellar nitrogen, oxygen, and krypton with the GHRS onboard HST
have recently found ``underabundances'' of these elements with respect to their
solar values. These findings are consistent with the subsolar elemental abundances
that have been measured in nearby B stars and are likely reflective of the current
ISM abundance pattern. Yet, in the case of interstellar sulfur, published GHRS
studies of ten individual sightlines reveal an abundance spread of about +/-0.2 dex
with a mean value near solar. We propose to more accurately determine the mean
abundance of interstellar S, evaluate its abundance spread, and search for any
density-dependent gas-phase S depletion based on an analysis of the 29 stars in the
HST archive with GHRS echelle observations of the S II Lambda1250 absorption-line
triplet. Most of this data has yet to be analyzed in detail, and no comprehensive
GHRS study of interstellar S has been carried out akin to the earlier work on N, O,
and Kr. Depending on the S abundance spread and whether or not a dust signature is
present, this study will more tightly constrain the interstellar S abundance
relative to solar, or better define the limits to which S can be used as an
interstellar abundance fiducial. The results will have potential implications
ranging from revisions in Galactic chemical evolution models to the growing use of
sulfur as a metallicity benchmark in QSO absorption-line studies of distant
galaxies.
------------------------------------------------------------------------------------
  Data Distribution

  Media:           ELECTRONIC
  Blocking Factor: 10
  Ship To:         PI_Address
  Ship Via:
  Email:
------------------------------------------------------------------------------------

                                                7996(  1) - 04/16/98 14:12  - [  2]

            Summary Form for Proposal  7996

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