[Aavso-photometry] Normal Variation in Tranformation Coefficients?

[Arne Henden]

Back from Yet Another Trip.
   How are you determining these coefficients - single field,
multiple fields per night, multiple fields but only one field per night,
etc.?
   Variation is expected - after all, you are fitting unique datasets
with linear least squares, so each fit should be randomly distributed.
However, Your (V-R) coefficient of 1.605 and the scatter in (V-I) seems large.
My older book shows some examples of the variation you should expect.
Arne
------------

Greg Crawford wrote:
> I have been calculating transformation coefficients over a number of nights.
> There is variation for each value. What range of variation is normal and what is
> unacceptable?
> 
> A table of my results, across a number of nights (and sometimes on the same
> night), shows:
> 
> B-V		 V		V-R		V-I
> 1.143		 0.047	1.124		1.224
> 1.182		 0.010	1.124		1.224
> -		-0.095	1.023		0.952
> -		 0.014	1.605		1.224
> -		-0.065	1.021		0.882
> 
> Should I assume this variation is normal and just average results, or is the
> variation suspect?
> 
> If they are suspect, what should I look for? As I understand my software, first
> order extinction coefficients affect the calculation of T/Cs because they are
> used to extrapolate to exoatmospheric magnitudes. So I assume extinction
> measurements could be suspect (light clouds perhaps?) Is SNR another factor?
> (That's why I left some B-V transformations above blank.)
> 
> 
> Greg Crawford
> 
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> http://www.nelsonbay.com/~gc/observatory.htm
> 
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