Have a Laugh on Me

["Thomas F. Droege" <droege@fastmail.fm>]

Yes, I am still here and working on the data.  

For about the last month, I have been struggling with a problem.  I
collect all the measurements of a star together, then I compute mean
values and sigma for each star.  I then sort the measurements for each
star and cut a selected range off the top and bottom of the list.  I
then compute mean and sigma for what is left. A plot of the resulting
mag vs sigma plot is attached.

The idea is to chop off the outliers that might be due to bad nights so
that the remainder can be searched for variability.  Real variables
should still have a large sigma, while the fixed stars should show a
sigma close to the expected value.  

I have been looking at this for days trying to figure out what is
special about 10.  I am not too embarrassed as I have found the problem.
Further, I am pleased that I noticed the problem at all. 
  
I assume that most of you can just look at the result and tell me what I
did wrong.  I will confess after I have given a few of you time to find
the error.  It is something that most of you would never do. 
-- 
  Thomas F. Droege
  droege@fastmail.fm

sigma_cropped.png