[Aavso-photometry] Ensemble photometry question

[arne]

Robert J. Modic wrote:
> I wondering what the best method was to calculate the
> total error of an ensemble of comp stars.  I know that
> the error decreases with the square root of the number
> of comp stars.  Since each comp star has its own error
> that is usually different from other stars in the ensemble,
> what formula should I use?
> 
Your best starting place is Kent Honeycutt's paper:
"CCD ensemble photometry on an inhomogeneous set of
exposures," 1992, PASP 104, 435.  He has the basic
error equation there.  This paper is required reading
for anyone performing ensemble photometry.

My error analysis is slightly different, since I take
into account the error between the instrumental measures
of each comp star and the "standard" magnitude for that
comp star as well.  The bottom line is that almost any
error analysis you make for your observation will be
a lower limit to the true error as you cannot know every
source of random and systematic error in your system.
Arne