7991(  1) - 04/16/98 14:09  - [  1]

    PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS   ST ScI Use Only
                                                       ID:      7991
                                                       Version: 1
                                                       Check-in Date: 16-Apr-1998
                                                                      14:07:15

1.Proposal Title:
The Photospheric Spectrum of Dwarf Nova Accretion Disks During Eclipse
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2. Proposal For  3. Cycle
AR               7
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4. Investigators
                                                                                     Contact?
    PI: Richard A. Wade                   Pennsylvania State University
   CoI: Jerome Orosz                      Pennsylvania State University                 N

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5. Abstract

We will analyze GHRS time-series ultraviolet spectra of two eclipsing cataclysmic
variable stars, UX UMa and RW Tri. These spectra were originally acquired to study
the behavior of the wind lines, but we will focus on modeling the photospheric
absorption spectrum that arises from the accretion disk in these binary systems. The
disk spectrum, out of eclipse, is a complicated sum of doppler-shifted lines formed
at many different temperatures over the face of the disk. During eclipse, smaller
portions of the disk are visible, with lesser ranges of doppler shift and
temperature, and the sweep of the occulting secondary star across the disk creates a
continually varying pattern of spectral line positions and strengths. We have
developed spectrum synthesis and eclipse geometry codes that allow us to predict the
spectrum at each orbital phase, given the geometry of the binary system and the
accretion disk parameters (most importantly the mass accretion rate). We will
compare our models directly with the data, avoiding uncertainties of interpretation
that are introduced in some eclipse mapping methods. Our goal is to check the
validity of state-of-the- art models against unique datasets in the HST archive, and
either infer the disk properties or improve and extend the models.
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  Data Distribution

  Media:           ELECTRONIC
  Blocking Factor: 10
  Ship To:         PI_Address
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                                                7991(  1) - 04/16/98 14:09  - [  2]

            Summary Form for Proposal  7991

  Item                         Used in this proposal
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  Proposal Category            AR
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