[Aavso-photometry] Transformation Coefficients

[Michael Crook]

Tim,

I will be observing LPVs and I understand it is
important to transform in these cases due to the
colour differences between the red variables and the
comparisons.   

Is there an 'idiots guide' available to transformed
differential photometry? (I mean a REALLY basic
guide?)

Cheers,

Mick 





--- Tim Crawford <tcarchcape at yahoo.com> wrote:

> While we still have somewhat of a related thread
> going
> RE this specific topic (Michael Koppelman's last
> post
> on the topic: Differential vs. absolute magnitudes)
> I
> thought I would post some recent values showing the
> difference between not transformed differential
> photometry and transformed differential photometry
> for
> the benifit of those of you who have never ventured
> into this territory.
> 
> This was a recent observation of V371 Per in which I
> had zero-pointed the instrumental magnitudes
> (meaning
> that the IM's would equal the sequence value) of the
> main Comp star; because of this particular action it
> makes it easy to look at this particular Spread
> sheet
> and pull off the following magnitude data.
> 
> Filter - Not Transformed - Transformed - Difference
> 
> V - 10.959 - 11.979 - .020
> 
> B - 11.563 - 11.575 - .012
> 
> R - 10.611 - 10.619 - .008
> 
> I - 10.217 - 10.230 - .013
> 
> It is important for you to understand  that other
> systems (scope/ccd/conditions) could have
> significantly larger differences or even
> significantly
> smaller differences (while pesumably the actual
> transformed values would have been quite close) on
> this same target, at the same time,  using the same
> comp(s) stars, depending on the calculated
> transformation coefficients for that system.
> 
> Tim Crawford CTX'
> Arch Cape Observatory
> 
> http://homepage.mac.com/windwalker1/ACObserv.htm
> 
> 
> 
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