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Image name: CCD_CHANGES_II.png (click image to enlarge)
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Date submitted: 13-Oct-1996
LWA, 13-Oct-96 CHANGES CAUSED BY TIME AND BY CCD BAKEOUT - II These images are intended to reveal changes in visible light response due to decontamination of the CCD. The LH column are made from the following pre- and post- bakeout exposures. 3-NOV-93 08:40:52 QT/H Diffu/Open Half Norm L 4 2.9 512x512 3-NOV-93 08:43:00 QT/H Diffu/Open Half Norm C 4 2.9 512x512 10-NOV-93 07:32:35 QT/H Diffu/Open Half Norm L 4 2.9 512x512 10-NOV-93 07:34:43 QT/H Diffu/Open Half Norm C 4 2.9 512x512 Note that in this case the histogram of the difference image is very nearly gaussian with a 0.5% shift towards a higher sensitivity. The difference image in the upper left has the color table offset by this 0.5% shift and shows the changes above (more contamination removed) and below (less contamination removed) average. The heavy contour, prepared from a boxcar smoothed image, traces the contour of average removal. The Oct-96 bakeout, 3-OCT-96 05:14:29 QT/H Diffu/Open Half Norm C 2 1.0 512x512 3-OCT-96 05:15:41 QT/H Diffu/Open Half Norm L 2 1.0 512x512 11-OCT-96 23:56:01 QT/H Diffu/Open Half Norm C 2 1.0 512x512 11-OCT-96 23:57:21 QT/H Diffu/Open Half Norm L 2 1.0 512x512 shows very little average change. In the upper right figure the heavy contour is the locus of zero signal level change. However, the general pattern here is for relatively strong signal enhancement in the corners and a signal _decrease_ in the center of the ccd. The effect in the corners is expected but the change in the center of the CCD is puzzling. In any case, it is clear that the bakeouts still have an effect and should be continued.