Analyzing Data

[Tom Droege <tdroege2@earthlink.net>]

I have been trying to push all the data through the pipeline that I have 
taken with the stars in constant position in the frame.  One of the things 
I am noticing as the analysis progresses is that this data is similar in V 
and I.  In the past, the I data had a larger spread at low magnitudes.

One difference is that I am throwing out data based on the median sky 
value.  I have watched data going by and set different levels for V and I 
based on losing about equal numbers of frames to the rejection.  I set it 
to lose a small fraction of the frames when the data looks clear.  This 
does a good job of clearing out dawn, dusk, and cloud data.

I am now looking at a data set go by where it is keeping most of the V data 
and rejecting all the I data (so far).  As Paul Bartholdi points out, the 
Clear Sky Detector sees the water vapor in the atmosphere, as does the I 
filter, I suppose.

Now suppose that a few high water vapor nights get mixed into a big pool of 
data.  These will have more noise, and thus might skew the distribution of 
the aperture photometry.  But I don't see how.  Any comments from the 
experts???

Tom Droege