Bias Frame

[Tom Droege <tdroege@veriomail.com>]

Because Jure has asked for it, I have added a bias frame to the exposure 
sequence.  I still do not have it quite right as the fits files are labeled 
one off.  A standard problem.  Sigh!  I tried to test it but did not get it 
right.  Not much lost as last night was a near full moon.

Dark (100 second) - Bias (1 second)  = Mean of 14  Sigma of 17  (ADU)

The dark current is thus about 0.35 e- per second at -23.5 C.  The 
temperature changed less than the measurement accuracy between the two 
exposures.  The data sheet indicates that we should be getting about 0.9 e- 
per second.  Close enough considering the uncertainty in an exponent.  I 
used dark current doubling every 5 C.

Note that the typical sky background is 40-50 ADU here.

This would indicate that the contribution of dark current is within the sky 
noise.  Of course, it is not so simple.  We have a few pixels that leak 
much more than others.

Tom Droege