Instrument Science Report WFPC2 2010-02:
Improved WF4 Anomaly Corrections
V. Dixon and J. Biretta
June 29, 2010
The WF4 anomaly is a temperature-dependent reduction in the gain of the WF4 CCD. Software added to calwp2 corrects stellar photometry to ~ 0.01 magnitude, but undercorrects the CCD bias level by several DN. While tracking down this discrepancy, we discovered three other complications that motivated us to construct a new set of reference files: a discontinuity in the WF4 anomaly between pixels in the image and the overscan region, unexpected structure in the overscan region for low-bias images, and an error in the application of the reference file by calwp2. New reference files that correct for these effects have been created and used to reprocess all low-bias images in the WFPC2 static archive.
The Complete Paper (PDF 0.95 MB) is available.