8378(  4) - 12/18/98 16:53  - [  1]

    PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS   ST ScI Use Only
                                                       ID:      8378
                                                       Version: 4
                                                       Check-in Date: 18-Dec-1998
                                                                      16:51:53

1.Proposal Title:
The Globular Cluster Luminosity Function as a Distance Indicator
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2. Proposal For  3. Cycle
AR               8
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4. Investigators
                                                                                     Contact?
    PI: Bradley Whitmore                  Space Telescope Science Institute
   CoI: Dr.  William Harris               McMaster University                           N
   CoI: Dr.  David Hanes                  Queen's University                            N

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5. Abstract

We propose to use existing WFPC2 images of nearby elliptical and S0 galaxies to test
the reliability of the Globular Cluster Luminosity Function (GCLF) for the purpose
of making distance estimates. The `standard candle' of this method is the turnover
point of the GCLF at M_V^0 ~eq -7.3 mag. The empirical evidence currently available,
mostly from the Virgo and Fornax ellipticals, is that the internal precision of the
GCLF turnover is +/-0.15 mag per galaxy, making the method competitive with even the
best distance indicators. However, there is tentative evidence that effects such as
dynamical evolution and differences in metallicity (among other second- order
parameters) may slightly alter the turnover point. This provides the opportunity to
reduce the already-small internal scatter of the method still further, and the
possibility of better understanding the origin and evolution of globular clusters.
We propose to pursue these goals by determining the GCLF for a sample of ~eq 80
galaxies from the archives, and searching for differences in the turnover as a
function of cluster color, position within the galaxies, and environment of the
galaxy. Our longer term goal is to use this data set to support a proposal using the
Advanced Camera for Surveys (ACS) to measure H_0 to within an internal precision of
5\ (external) precision of 7.
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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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                                                8378(  4) - 12/18/98 16:53  - [  2]

            Summary Form for Proposal  8378

  Item                         Used in this proposal
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  Proposal Category            AR
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