9526(  1) - 12/06/01 12:37  - [  1]

    PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS   ST ScI Use Only
                                                       ID:      9526
                                                       Version: 1
                                                       Check-in Date: 06-Dec-2001
                                                                      11:45:25

1.Proposal Title:
Characterization of Spatial Variations in the Transmission of WFPC2 Filter FQCH4N-D
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2. Proposal For  3. Cycle
AR               11
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4. Investigators
                                                                                     Contact?
    PI: Erich Karkoschka                  University of Arizona

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5. Abstract

The WFPC2 filter FQCH4N-D (890 nm) has probably a spatially variable transmission
curve. This is estimated to cause photometric inconsistencies across the field of
view of up to 30 percent, much larger than for other WFPC2 filters where flatfields
describe the spatial photometric variation to better than 0.3 percent consistency
according to the WFPC2 Handbook. This undocumented feature of FQCH4N-D affects a
number of investigations with HST since this is one of the WFPC2 filters most often
used for solar system studies. More than 600 images have been taken with FQCH4N-D.
During Cycle 10, observations of Saturn with this filter will quantify the spatial
variation of the filter transmission characteristics. I propose to analyze those
observations and to provide the size and the direction of the effect, as well as
estimates on how this may affect photometry based on imaging of giant planets and
Titan with this filter. Similar data is published for ultraviolet filters with red
leaks but still missing for FQCH4N-D. I successfully completed two previous
investigations for the calibration of WFPC2.
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                                                9526(  1) - 12/06/01 12:37  - [  2]

            Summary Form for Proposal  9526

  Item                         Used in this proposal
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  Proposal Category            AR
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