[Aavso-photometry] Question about identifying ref stars and SNR

[arne]

bailyhill at aol.com wrote:
> Hello All
>  
> I am sorry to see the CCD box go--but I understand the confusion.  For 
> me, the Photometry Table with RA and Dec just does not work.  Its too 
> much work to get the values.  I have only done it once, and that was for 
> a star that had 10 Years of history that we wished to continue.  I had 
> to use a scale/ruler, get out my calculator, covert units, draw lines on 
> the chart, etc.  Big PITA.
>  
I am lost here - if the star has a label of say 143, and that label is
in the photometry table, then why do you need a ruler, calculator etc.
to find the star?

> The idea of a radial distance is a little better, but still does not do it.
>
I think in 9 cases out of 10 it will solve the problem.  Let's try it and see.
Even with coordinates, it is easy to see which comp star is north of the
other by looking at the coordinates, and identify them uniquely.  It is
really a simple problem unless I'm misunderstanding something.

> A suggestion---How about only incuding one of the "113" stars in the 
> chart and the CCD Box.  This would eliminate the ambiguity and still 
> keep the chart quite user friendly. 
>  
> I suppose at times, having two comps, 113, with different B-V's might be 
> usefull.  However, for most of our projects, are there other advantages 
> to keeping both? 
> 
The first problem here is for a field that only includes one variable
and its sequence.  In that case, the original sequence had incorrect
magnitudes, and when the correct magnitudes are used, the labels
become identical.  The proper way to correct this is to modify the
sequence, which is Phase III in the process.  This is a slow process
as you have to look at each sequence star again, now that you have
superior knowledge about its magnitude, color and variability, and
see if it is proper for a given variable.  For this, you just have
to wait - sorry!  In the meantime, the photometry is correct - you
can use either identically-labelled star for your estimate.

The second problem is if you use a chart size sufficiently large that you
start including the sequence of a second variable.  Then you can often
have two stars with identical labels, one in each sequence.  That needs
to remain - now, you can use the radial distance or coordinates
to easily choose which sequence star is proper for the variable you
are studying.
Arne