Stacking

[Tom Droege <tdroege@veriomail.com>]

There was a hole in the clouds so I took some data with TOM1 where I 
alternated 50 and 400 second exposures.  The results were not as good as I 
had hoped.  The alignment of TOM1 is just not good enough for 400 second 
exposures.  The stars are all little diagonal lines.  About 5-6 pixels 
long.  While 100 second exposures look pretty good, 400 is just too 
long.  One gains a little with longer exposures since the fraction of time 
taking exposures is longer (less time spent reading out).  But I think 
there will be problems detecting stars.

Has anyone tried stacking the images of DS20 before star detection?  One 
might stack the exposures in groups of 8 and gain about a magnitude, or 
stack all 56 and gain 2 magnitudes.  There are lots of possible strategies 
with this data.  I have sensed a reluctance to stack from the group in the 
past.  Why?  I would think that it should not take too much time since one 
can compute an offset from the first and last images in a sequence and get 
pretty close.

Tom Droege