8354(  4) - 12/18/98 16:43  - [  1]

    PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS   ST ScI Use Only
                                                       ID:      8354
                                                       Version: 4
                                                       Check-in Date: 18-Dec-1998
                                                                      16:41:45

1.Proposal Title:
DIRECT Distances to M31 and M33 Using Detached Eclipsing Binaries and Cepheids
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2. Proposal For  3. Cycle
AR               8
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4. Investigators
                                                                                     Contact?
    PI: Dimitar Sasselov                  Harvard-Center for Astrophysics
   CoI: Dr. Krzysztof Stanek              Smithsonian Astrophysical Observatory         N
   CoI: Mr. Lucas Macri                   Harvard-Center for Astrophysics               N

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5. Abstract

We propose to use the archival observations by the HST/WFPC2 in two important
galaxies in the cosmological distance ladder, M31 and M33, to identify the variable
stars we have already discovered from the ground. The new variables come from our
project, called DIRECT, aiming to obtain the distances to M31 and M33 using detached
eclipsing binaries and Cepheids. Combining photometry and spectroscopy for a
selected subsample of binaries and Cepheids allows us to derive direct distance of
high accuracy, which rely on no intermediate steps. We expect to identify 20--30\
HST/WFPC2 images, thus improving significantly their photometry by quantifying
systematic effects due to crowding. This should aid in both the accuracy and
precision of our direct distance determination to M31 and M33, which are stepping
stones for most of our current efforts to understand the evolving universe at large
scales. Thus we expect to help in decreasing the HST Key Project's overall
uncertainty in deriving the Hubble constant, H_0, by a factor of 2 (or to about 5.
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  Data Distribution

  Paper Products:  NO
  Media:           ELECTRONIC
  Blocking Factor: 10
  Ship To:         PI_Address
  Ship Via:
  Email:
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                                                8354(  4) - 12/18/98 16:43  - [  2]

            Summary Form for Proposal  8354

  Item                         Used in this proposal
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  Proposal Category            AR
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