[Aavso-photometry] V filter only - transforms possible?

[Tom Krajci]

To continue this thread...

Last night I made up a spreadsheet where I measured instrumental 
magnitudes of some V filtered images of M67.  The stars I measured are 
Henden stars with known B-V color index and V magnitude.  I plotted   V 
- Instr.Mag   versus   B-V   for these stars, and then found the slope.  
(Thanks to Brian Warner for making sure I had the right info in the 
spreadsheet.)

If I understand things correctly, I can use this slope as the transform 
value when working fields well known/calibrated mags and colors for 
comps and targets (or at least a good assumption of target color).

If anyone is curious, I can send them a copy of this spreadsheet...which 
I consider a student/preliminary lab exercise that helps me understand 
this issue a bit better.  (The spreadsheet has two sheets.  One is based 
on a Brian Warner image, and the other sheet is based on two of my 
images.  Each scope/CCD/filter will have a different resulting slope, 
but the agreement between my two exposures is pretty good.)

For calibrated fields...I am hopeful that I can do decent 'transformed' 
work with single-color-only measurements.

Yes, I'll make sure that the transform value and assumed target color 
are mentioned in the comments of any reports/papers.

Happy Holidays!

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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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