9219(  1) - 12/20/00 23:46  - [  1]

    PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS   ST ScI Use Only
                                                       ID:      9219
                                                       Version: 1
                                                       Check-in Date: 20-Dec-2000
                                                                      23:39:29

1.Proposal Title:
Pushing the limits of variable stars detection with HST
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2. Proposal For  3. Cycle
AR               10
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4. Investigators
                                                                                     Contact?
    PI: Dimitar Sasselov                  Harvard-Center for Astrophysics
   CoI: Dr. David Bersier                 Harvard-Center for Astrophysics               N
   CoI: Dr. Christophe Alard              Institut d'Astrophysique de Paris             N
   CoI: Mr. Lucas Macri                   Harvard-Center for Astrophysics               N

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5. Abstract

We propose to use the novel method of image subtraction designed to find variable
stars, and apply it to HST/WFPC2 data of the galaxy NGC 4603. This galaxy has been
observed to discover Cepheids and obtain a distance. It is the most distant galaxy
in which Cepheids have been found and the resulting distance may be affected by
systematic errors, most notably the fact that non-variable stars contaminate the
sample of Cepheids. The image subtraction technique offers a better way to find
variable stars in very crowded environments. We will use this technique to find
Cepheids in NGC4603 and obtain light curves. We will assess the reality of the
variables found previously and it is likely that we will find more Cepheids.
Combined with standard PSF photometry, we will be able to obtain a more accurate and
more reliable distance to this galaxy.
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                                                9219(  1) - 12/20/00 23:46  - [  2]

            Summary Form for Proposal  9219

  Item                         Used in this proposal
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  Proposal Category            AR
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