[Aavso-photometry] Transformation coefficients - Aavso-photometry Digest, Vol 52, Issue 11

[Brad Walter]

Hey Tim, are you trying to see if we are paying attention? I think you had a
wandering finger entering the untransformed V mag in your e-mail.  This
tally's with the scale of the differences I get on the infrequent occasions
when I transform magnitudes. That reminds me, that I haven't calculated new
transformation coefficients since I replaced my filters last year. I guess I
better take some images of M67 while it is in good position. 
 
> 
> Message: 2
> Date: Mon, 10 Mar 2008 15:52:18 -0700 (PDT)
> From: Tim Crawford <tcarchcape at yahoo.com>
> Subject: [Aavso-photometry] Transformation Coefficients
> To: aavso photometry <aavso-photometry at aavso.org>
> Message-ID: <200081.33556.qm at web34402.mail.mud.yahoo.com>
> Content-Type: text/plain; charset=iso-8859-1
> 
> 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
> 
>