8352(  2) - 12/18/98 16:42  - [  1]

    PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS   ST ScI Use Only
                                                       ID:      8352
                                                       Version: 2
                                                       Check-in Date: 18-Dec-1998
                                                                      16:40:40

1.Proposal Title:
Physical Conditions in Predominantly Atomic Interstellar Clouds
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2. Proposal For  3. Cycle
AR               8
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4. Investigators
                                                                                     Contact?
    PI: Steven Federman                   University of Toledo
   CoI: Prof. David Lambert               University of Texas                           N
   CoI: Dr. Daniel Welty                  University of Chicago                         N

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5. Abstract

We propose to determine the physical conditions in interstellar sight lines from
archival GHRS spectra showing absorption from C I. The choice of sight lines is
based on the fact that observed molecular abundances are relatively low. Analysis of
the relative populations among fine structure levels in neutral carbon will yield
estimates for gas density and temperature. We will incorporate published results on
rotational excitation in H_2 to help constrain the gas temperature. The high quality
data on C I, examined with our refined self-consistent set of oscillator strengths,
will provide accurate estimates of gas density. We will use the results from C I
excitation to further our studies in two areas. We will examine the extent of a
separation into low and moderately dense neutral material within a single cloud
toward stars in Scorpius and Ophiuchus and whether such stratification is a common
feature of interstellar clouds and therefore must be included in studies of
interstellar material on galactic scales. We will also obtain information on the
amount of CH associated with CH^+ synthesis as an aid to understanding CH^+
formation in the low density portions of interstellar clouds, an unsolved problem
despite nearly fifty years of study.
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  Data Distribution

  Paper Products:  NO
  Media:           ELECTRONIC
  Blocking Factor: 10
  Ship To:         PI_Address
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                                                8352(  2) - 12/18/98 16:42  - [  2]

            Summary Form for Proposal  8352

  Item                         Used in this proposal
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  Proposal Category            AR
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