11244(  1) - 03/30/07 11:03  - [  1]

                  HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 11244

Version: 1    Check-in Time: 30-Mar-2007 15:03:29       STScI Edit Number: 0

Title
WFPC2 CTE and Photometric Zero Points
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Type             Cycle     Parallel Pointing Tolerance
AR               16        <none>
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Investigators
                                                                                     Contact?
    PI: Dr. Andrew Dolphin                Raytheon Company

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Abstract

With charge-transfer efficiency (CTE) losses of several tenths of a magnitude in
many current exposures, the accuracy of CTE corrections is a limiting factor in the
accuracy of photometry that can be obtained with WFPC2. However, the CTE corrections
in common use are five years old, and thus corrections for CTE loss on current
observations are made with the dangerous assumption that CTE loss has continued
growing over the past five years at the rate it grew for the instruments first eight
years of service. The uncertainty caused by this assumption implies that the use of
these old CTE corrections is the dominant error source in many WFPC2 images, and
will become even worse in Cycle 16 as the extrapolation increases. This proposal
seeks to remedy this situation by undertaking an examination of CTE using data of
the Omega Cen calibration field obtained over the entire lifetime of WFPC2. The
methodology has been proven to produce accurate CTE corrections (indeed, they are
the recommended corrections in the WFPC2 handbook and online CTE calculator).
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