[Aavso-photometry] Transformation Coefficients

[Tim Crawford]

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