Affiliation
American Association of Variable Star Observers (AAVSO)
Wed, 05/25/2016 - 18:59
I see this term (also Tri-B and Tri-R) used in the light curve generator. Does this mean a magnitude from a system using a tricolor G filter which has been transformed to V? ...or perhaps it means a magnitude from a system using a G filter as if it were a V filter, i.e. using the standard V mag in the comp stars for differential photometry.
Phil
Hi Phil,
Since this was set up a few years ago under my direction, I'll reply. The intent was Tri-G to be tricolor G, using V-magnitude comparison stars, not transformed.
If TG is transformed to the V-magnitude system, then it should be reported as V. Since this is taking one filter system and transforming it to another, I also suggest that a note be placed on the record indicating that the native filter was tricolor-G.
It is of course possible to obtain TG calibration of a field, and then report the tricolor-G observations on some tricolor-G standard system, using comparison stars that had tricolor-G magnitudes. I don't think it exists, but for completeness, that would be a possibility. The AID was not set up to handle that situation.
I hope that helps!
Arne
Thanks, Arne. That's exactly what I wanted to know.
One of the students in the CCD Photometry-II class from Slovakia, lacking photometric filters, transformed his tri-color RGB filters to standard Rc,V, B. using the subset of M67 standard stars in Chapter 6 of the CCD Photometry guide. The tables and plots looked good to me. Today he posted his transformed measurements of RU Vir and used AAVSO sequence star 105 ( B-V 1.18) as a check star. I was impressed with his results.
I have not seen this done before (transforming RCB to Rc,V,B) so I don't feel qualified to make any judgement on his work. Would you be willing to take a look at his transform plots and photometry report on RU Vir, particularly in regard his transformed measurements of the check star? They are neatly packaged in two screen shots.
I can send the screen shots to you privately.
Phil
Hi Phil,
I'll look at the information on the CHOICE course forum and respond there.
Arne
Hi all,
I dug up this very old message ...
A friend asked me a question I was unable to answer with certainty.
Would an observer using a monochromatic b&w cmos astro camera, and some classic non photometrical RGB filters, be considered as doing TriR, TriG and TriB photometry, as DSLR owners are doing, and should he report his observations as TR/TG/TB ?
Thanks you so much in advance,
Christophe
Yes. The magnitudes would be reported as filter TG,TB,or TR using V,B, or R comparison stars.
Barbara
Sounds good to me. You’re making the same observations as a DSLR sensor, but using separate filters. Most DSLR sensors use two green measurements for each red and blue, however. You should initially pick stars where there are DSLR observers submitting observations and compare your results. Without transforming to Johnson V, you should report as Tricolor.
Photometric filters are pretty expensive and can be hard to acquire.
John
Hi John. I think supply issues with photometric filters have eased and they are much more available now than they were a few years ago. I've purchased some recently as have some others I know with no issues.
-Walt
Thanks all,
Great and good replies !
Christophe