[Aavso-photometry] Transforming

[Tom Krajci]

>From: "Barbara G. Harris" <barbharris1 at hughes.net>

>Here are the TCs that I obtained about 1 month ago.  I re-imaged M67 a few
>nights ago to see how repeatable my numbers were but I have not performed
>the calculations yet for those images:
>Tbv:  1.268
>Tvr:  0.981
>Tri:  0.868
>Tv:  -0.189
>Tr:  -0.173

>What do the negative numbers for Tv and Tr signify?  

It means (for Tv) an X/Y plot of catalog values for V-R (x axis) versus your values for v-V (y axis)...has a negative slope.  That means your values of v-V for stars with large V-R tend to be a bit low, and your values of v-V for stars with small V-R tend to be a bit high.

>How do I know if a
>particular star that I am observing has a constant color?

I would assume that a constant star is also constant color.  (Are there any examples of variables that break this rule?)

If you want, you could zip up and email me a handful of your calibrated 
M67 images (1 month old and recent ones) and I could look them over, 
compare them to some that I've taken, etc.

-- 
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Tom Krajci
Cloudcroft, New Mexico
http://picasaweb.google.com/tom.krajci

Center for Backyard Astrophysics (CBA)
http://cbastro.org/ CBA New Mexico

American Association of Variable Star
Observers (AAVSO): KTC http://www.aavso.org/
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