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WFC3 Data Handbook V. 4.0 |
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5.5 5.5.1 GhostsScattering between the UVIS CCD and either the detector, or dewar window forms so-called ‘optical’ ghosts. These ghosts are separated by ~80 arcsec from their source generally in pairs (a "figure eight"). Further details may be found in WFC3 ISR 2001-17, WFC3 ISR 2004-04 and WFC3 ISR 2007-21.5.5.2 Stray Light5.5.3 Cross TalkFigure 5.7 shows a UVIS image with CT (from WFC3 ISR 2009-03). The UVIS crosstalk is linear, negative, and appears at the level of ~10-4 to 10-5 of the source. Specifically, in full-frame, unbinned UVIS readouts, the CT level is ~2x10-4 of the source when the target is in quadrants A or C and about 8x10-5 when the target is in quadrants B or D (WFC3 ISR 2009-03).A standalone IDL procedure is available for correcting UVIS data for crosstalk, effectively restoring pixels to a mean, which is well within 1 sigma of the mean of surrounding pixels. The code as well as a description of its use is available as part of WFC3 ISR 2012-02.Figure 5.7: UVIS Crosstalk.UVIS chip image taken from the PSF Wing calibration proposal 11919, shown with a hard stretch to emphasize the CT. The slightly saturated star is in the B quadrant at right; the resulting mirror image CT (circled) is in the A quadrant at left. The partial dark column below and to the left of the PSF is a bad column.