[Aavso-photometry] Normal Variation in Tranformation Coefficients?

[Michael Koppelman]

Are you doing zeropoints every night?

On Jun 14, 2004, at 10:52 AM, 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
>
>       *
>          *
>    *
>        *
>
>       *
>
> http://www.nelsonbay.com/~gc/observatory.htm
>
>
>
>
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