> Using GRIM last night I noticed 4 blobs (spots) on the GRIM images > that I hadn't noticed. > They show up well after subtracting a dark ... > and look like stars in mediocre seeing conditions. > ... > Although these blobs don't subtract out with the dark, they seem to > subtract out well when subtracting an offset-position from an > on-position. > Eddie pointed out that these are not bad pixels, but must be > reflected light. Must is a very strong word. I've seen something that sounds exactly like this with another NICMOS-3 camera. In that case, the blobs disappeared after a few days. We decided that the most likely culprits we could think of were someone (not me!) burning a stellar field into the chip or some kind of local stress, but we never were sure. Alan Watson APO APO APO APO APO Apache Point Observatory 3.5m APO APO APO APO APO This is message 23 in the apo35-grim archive. You can find APO the archive on http://www.astro.princeton.edu/APO/apo35-grim/INDEX.html APO To join/leave the list, send mail to apo35-request@astro.princeton.edu APO To post a message, mail it to apo35-grim@astro.princeton.edu APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO