Re: Calculation of mag errors

[Stupendous Man <richmond@stupendous.cis.rit.edu>]

> Now that you have done all the dirty work of
> setting up the statistics for the annulus, is this
> a good time to revisit estimating this error?
> One might be able to estimate things like
> background curvature - if too big, go to a
> smaller annulus and accept the higher random
> error in exchange for the smaller systematic
> error. I never tried to do this: I couldn't see how
> to do it in a manner that was not horribly
> sensitive to nearby confusing stars.

  Hmmm.  I don't see any easy way to add this sort
of decision-making intelligence to the pipeline
without a _lot_ of work.  

  What _is_ easy is to modify one of the parameter
files: a simple ASCII text file, not code.  The 
"stars.param" file has a section which looks like this:

# parameters controlling the "phot" program
apers         { V { 4 } }    { I { 4 } }  
sky_inner     { V  10   }    { I  10   }
sky_outer     { V  20   }    { I  20   }
readnoise     { V     15   } { I     15   }
gain          { V      2.4 } { I      2.4 }
saturate      { V  20000   } { I  20000 }


  One can place several aperure radii into the first parameter,
so that all stars are measured through several different
apertures, and the results all processed.  One could
then look at the results after one night, or one week,
and figure out which value gives the best result for a given
camera under typical conditions.  I suspect that Tom
has done some optimizing of this sort ....


                                   Michael Richmond