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What is Tri-G magnitude

spp
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

HQA
Affiliation
None
Wed, 05/25/2016 - 19:48
Tri-G magnitude

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

spp
Affiliation
American Association of Variable Star Observers (AAVSO)
Thu, 05/26/2016 - 02:38
Tri-G

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