|Documentation > SXT Observation Notes > this page|
Image name: CCD_CHANGES_I.png (click image to enlarge)
Image size: 773.367 KB (1024x982)
Date submitted: 13-Oct-1996
LWA, 13-Oct-96 CHANGES CAUSED BY TIME AND BY CCD BAKEOUT - I This array of images demonstrate the changes in the CCD caused by 3 years of operation (LH column) and by a CCD bakeout at each of the two epochs. The LH images were prepared (flattened) with the program SXT_DIFUSER2 from the pairs of observations indicated by *: 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 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 Note the evolution of radiation damage in both diffuse and discrete (specks) features. The lower RH image is the difference of the Oct-96 pre-bake flattened image and its corresponding pre-bake diffuser image. The corresponding Nov-93 difference is pretty flat -- with a gaussian histogram. The Oct-96 bakeout had more non-gaussian structure. Perhaps this is caused by the larger period between bakeouts (7 months) in this case. The Nov-93 bakeout was only 3 months following the previous CCD bakeout. The pointing for the 3 bakeouts was: 482.300 603.800 482.190 603.450 483.590 602.450 483.990 601.950 for the Nov-93 set and 536.180 594.810 536.430 594.790 537.730 592.760 537.950 592.270 for the Oct-96 set. This difference in pointing makes it difficult to directly compare the intensity pattern for the two cases. However the difference of the flattened (uppper and lower LH images) images, shown in the upper right, indicates the 3-year changes in radiation damage. Here dark means additional radiation damage. It appears that some healing may have taken place at the west limb area. The enhanced horizontal streaking in the corners of the Oct-96 difference image is probably evidence for contamination which orients along the CCD gate grooves. This was observed to happen in pre-launch studies of contaminated CCDs. It should be mentioned that I still do not fully understand why the diffuser images reveal the pattern of radiation damage.