9217(  1) - 12/20/00 23:45  - [  1]

    PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS   ST ScI Use Only
                                                       ID:      9217
                                                       Version: 1
                                                       Check-in Date: 20-Dec-2000
                                                                      23:39:00

1.Proposal Title:
Determining D/H Ratios and Physical Conditions in Local Interstellar Gas Using White
Dwarf Probes
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2. Proposal For  3. Cycle
AR               10
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4. Investigators
                                                                                     Contact?
    PI: Meena Sahu                        Goddard Space Flight Center
   CoI: Dr. Wayne Landsman                Raytheon/ITSS                                 N
   CoI: Dr. Fred Bruhweiler               Catholic University                           N
   CoI: Dr. Martin Barstow                Univ. Leicester                               N
   CoI: Dr. Jay Holberg                   Univ. Arizona                                 N
   CoI: Dr. Ivan Hubeny                   Goddard Space Flight Center                   N
   CoI: Dr. Jeff Linsky                   Univ. Colorado                                N
   CoI: Mr. Don Lindler                   Advanced Computer Concepts                    N
   CoI: Dr. Ted Gull                      Goddard Space Flight Center                   N
   CoI: Dr. Charles Bowers                Goddard Space Flight Center                   N
   CoI: Dr. Thiery Lanz                   Goddard Space Flight Center                   N

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5. Abstract

Using archival GHRS and STIS spectra toward 21 white dwarfs (WDs) located within 200
pc, we propose to determine the D/H abundance ratios and physical conditions in the
intervening diffuse Local Interstellar Medium (LISM) clouds. Our study will result
in emph7 new D/H ratio measurements (toward GD659, REJ0503-289, EUVEJ1126+18.6, V471
Tau, Feige 24, 2REJ1032+532 and 2REJ2156-543), which represents a 41\ in the number
of known D/H measurements in the LISM. Our results will be used to extend the 3D
model of local clouds constructed by Linsky & collaborators. N/H measurements in the
LISM are possible only by using WD spectra (as opposed to late-type star spectra).
We will derive N/H ratios for these WD sightlines and compare them with the diffuse
ISM value. We will test a recently reported claim on the anticorrelation of the D/H
and N/H ratios in more distant diffuse ISM clouds and explore its possible causes
and its implications for the LISM. We will obtain emph2 new electron density
measurements in the LISM and combine them with published measurements to test
predictions of the models constructed by Bruhweiler & collaborators which suggest
that the electron density should vary in the Local Interstellar Cloud (LIC) and that
it should increase near its interface with the surrounding 10^6 gas.
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                                                9217(  1) - 12/20/00 23:45  - [  2]

            Summary Form for Proposal  9217

  Item                         Used in this proposal
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  Proposal Category            AR
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