[Aavso-photometry] Ensemble photometry

[Jim Roe]

I'm trying to understand and learn how to do "ensemble photometry" 
because I have come to believe that it will produce more accurate and 
precise results.  Right?  I have re-visited threads on the list, 
Googled, read several papers but I have yet to find a clear, concise 
definition of the technique.  E.g.,

Honeycutt (PASP 104:435-440, June 1992) states: "A simple (and often 
quite adequate) technique for CCD ensemble photometry is to calculate 
the difference between the instrumental magnitude for the program star 
and a comparison magnitude obtained from the sum of the intensities of 
perhaps a dozen of the brighter stars which appear in each exposure of 
the series."  This doesn't seem right to me, perhaps it is a typo that 
was mentioned in an earlier post.

In another paper on the web by Hayes-Gehrke 
<http://www.astro.umd.edu/~avondale/extra/Variability.html>
it is stated "Ensemble averages make this technique even more reliable. 
Given at least a few dozen stars in the image, the assumption is made 
that the average magnitude of these stars would remain constant from 
frame to frame, regardless of the type or behavior of the individual 
stars. "  This makes more sense to me.

Finally, The MaximDl manual says: "If you tag more than one reference 
star, you must set the magnitude for each; the results will be 
averaged."  Does this, then, constitute "ensemble photometry?"

If so, and I would just as soon continue using Maxim given my $400 
investment therein, several questions arise.

Which extra reference stars should I include?  Presumably only from 
those for which photometry exists, but sometimes (often) there are 
photometry stars that are much fainter than the program star and, unless 
I expose for good S/N on them, their measurement errors will be greater 
and it would seem adding them to the "ensemble" will degrade the whole 
system.

Would I consider all of the individual reference stars to be check stars 
to be compared to the ensemble average?

Jim Roe [ROE]
Wentzville, Missouri