9216(  1) - 12/20/00 23:45  - [  1]

    PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS   ST ScI Use Only
                                                       ID:      9216
                                                       Version: 1
                                                       Check-in Date: 20-Dec-2000
                                                                      23:38:46

1.Proposal Title:
Faint Photometric Standard Fields for HST
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2. Proposal For  3. Cycle
AR               10
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4. Investigators
                                                                                     Contact?
    PI: Abhijit Saha                      NOAO
   CoI: Dr. Brad Whitmore                 Space Telescope Science Institute             N
   CoI: Dr. Peter Stetson                 Dominion Astrophysical Observatory            N
   CoI: Dr. Stefano Casertano             Space Telescope Science Institute             N
   CoI: Dr. Ralph Bohlin                  Space Telescope Science Institute             N

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5. Abstract

Some of the most important projects with the most expensive telescope ever built ---
HST --- are hostage to the uncertainty in the absolute calibration of its
photometric system. The standard practice in the past has been to calibrate faint
objects (e.g. V=26) observed with long exposures using bright stars (e.g. V=13)
observed with very short exposures. There is now good evidence that this is the main
cause of uncertainty in the absolute photometric accuracy of WFPC2 on HST. We
propose to use the Mini-Mosaic Imager on the WIYN telescope to establish faint star
photomteric sequences to V=22 in carefully chosen fields that have already been
repeatedly observed with WFPC2. This will allow us to retroactively recover the
history of the absolute calibration of WFPC2 throughout its mission, and hence
improve the available photometric accuracy for all WFPC2 observations. Future HST
observations of these fields will allow us to follow WFPC2's absolute calibration to
the end of its mission, and may later serve as the basis for calibrating ACS and
WFC3. This will greatly reduce the error budgets for a wide variety of fundamental
projects (e.g., extragalactic Cepheids and RR Lyrae stars; supernovae; globular-
cluster ages; distance and metallicity estimates from colors and magnitudes of red
giant branch tips).
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                                                9216(  1) - 12/20/00 23:45  - [  2]

            Summary Form for Proposal  9216

  Item                         Used in this proposal
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  Proposal Category            AR
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