Subject: Re: stray light in GRIM

From: Alan Watson

Submitted: Wed, 24 Jul 1996 12:21:11 -0600

Message number: 23 (previous: 22, next: 24 up: Index)

> 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
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