Hi all,
I have just started doing some photometric measurements with my imaging color filters. They are Baader planetarium imaging filters with a square transmission profile. To make them more usefull I generated transformation coeefficients with TG on the NGC 7790 starfield. By the way, the red filter transform was just for fun/info. I won't use that filter for measurements as the transmission profile of the Red imaging filters is too far of Johnson R.
My question is; how to interpret these coefficients. Is it any good? How usefull are my measurements if i report them as Johnson B and V. I have read that transforming these kind of imaging filters can be usefull, but not on redder stars. On what B-V index should I aim for my targets and comps? lower then +1,0 of +1,5?
Kind regards,
Remco Kemperman
I forgot to add my coeeficients. so:
[Setup]
description= TG - Version 6.6, Telescope= KREA, Time created (UT) = 2021_11_27_20:32:49
[Coefficients]
Tbv= 1.519
Tb_bv= 0.240
Tbr= 1.226
Tb_br= 0.157
Tv_bv= -0.097
Tvr= 0.911
Tv_vr= -0.182
Tr_vr= -0.084
[Error]
Tbv= 0.012
Tb_bv= 0.006
Tbr= 0.007
Tb_br= 0.004
Tv_bv= 0.008
Tvr= 0.005
Tv_vr= 0.014
Tr_vr= 0.016
[R Squared Values]
Tbv= 0.998
Tb_bv= 0.971
Tbr= 0.999
Tb_br= 0.968
Tv_bv= 0.806
Tvr= 0.999
Tv_vr= 0.800
Tr_vr= 0.440
Remco,
I also have Baader RGB filters. Your transforms for NGC 7790 are similar to mine:
Tbv = 1.599 Tb_bv = 0.325 Tv_vb = 0.057
Tvr = 0.961 Tv_vr = -0.102 Tr_vr = -0.047
As soon as I have a few clear nights I plan to test the results of the V-R transforms by measuring a few Landolt standard stars, including one or two red stars (B-V >1.5). I'll be happy if I get good transformed magnitudes in V and R. I don't have much in the way of expectations for the B-V transforms.
Phil
Hi Phil,
thanks for the info.
In the meanwhile I have done some measurements on Nova Cas and RW Cep en S Cep with these transform coefficients I generated. The latter two (S Cep and RW cep) are both B-V > 1,5. I noticed that the V-magnitude is pretty much spot on with other peoples observations. The B measurements or a bit of though sometimes.
Remco
Remco,
I intended the tricolor to J/C transforms to be a way for those without access to J/C filters to use their Green filters to produce good, transformed magnitudes. I think the transformed Red to R magnitudes will probably be good as well. I have no such expectations for the Blue to B transforms although there has been some discuss about this on another forum.
I plan to test this by observing Landolt standard stars, but the cloudy, foggy winter weather has now descended here. This make take a while. If you have good weather I would encourage you also to use your transforms, including the Blue to B to observe Landolt stars.
Phil
I am lead on the science team for the RASC's remote telescope (0.4m RC cass) at Sierra Remote Observatories. The prime focus (<-pun) for the telescope is pretty picture imaging so we are restricted to LRGBHaOIIISII filters. Our observing so far has been almost exclusively unfiltered CV. However, to assist in science observing I attempted transforms from RGB to BVR from M67 images. Coefficients found were:
Tbv = 1.540 Tb_bv = 0.420 Tv_bv = -0.108 Tvr = 0.752 Tv_vr = -0.212 Tr_vr = 0.036
Std errors on all were 0.023 to 0.045.
Richard