Re: Winter Project

["Thomas Droege" <tdroege2@earthlink.net>]

Yet one more thing.

> I already compute this file.  It is labeled all.t and is one of the things
> generated by my "process everything" program.  I can send this file to
> anyone that wants it.  It is the one that I just quoted to someone.
(Arne).
> It has the following star count:
>
> One or more hits	18,169,758
> three or more 		7,233,061
> 5 or more 		3,997,689
> 10 or more		1,560,290
> 20 or more		498,386
>
> This program computes sigma for each star from all the measurements.  I
> have another program that computes sigma after excluding a variable number
> of above and below the mean stars.   I use this one for hunting for
> variables so I do not presently output a list of the stars other than as
> plot files for the stars that meet all the requirements.
>

If there was a statistics problem (not enough measurements of each star)
then one would expect the nature of this plot to change as more and more
statistics were collected.  I have been continually making such plots since
Michael introduced me to them and I learned enough Perl to do the
computations.  It just makes no difference as I go from 3 to 10 to 20 point
plots.  Something else is going on.

I kept trying things.  I did all kinds of computations in an attempt to
change the appearance of the mag-sigma plot.  Nothing seemed to help. 
Well, a few data runs where I tracked a field very tightly had a better
distribution.  A clue?  Finally I got the clue from Richard Berry that the
problem was probably due to the transparency of the gate electrode which
covers only part of the CCD cell.  This limits accuracy to somewhat below a
sigma of 0.1 mag.  

I think this is really the thing that limits the spread of our results.   I
see no cure other than to replace the chips with thinned back illuminated
chips.  This is about a $250,000.00 project.  I don't plan on it.  

Tom Droege