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Thu, 12/02/2021 - 18:59
Good day.
I'm currently applying what I've learned from the previous CCD Photometry II course 2021 and calculated transformation coefficients for our main telescope set-up, Meade LX850 16" SCT and SBIG STT-8300MM CCD camera with Baader RGB (non-photometric) filters.
Here is the link of screenshot showing the results made using the spreadsheet method for NGC7790: https://drive.google.com/file/d/12dOYVSsRJdqQ6rQakKP-bjXs5vqO3b7b/view?usp=sharing
I hope I did everything correctly. Your feedback will be greatly appreciated. Thank you very much.
Best regards,
Aldrin
P.S. Due to some internet issues, this topic was unexpected posted twice in the forum. Kindly delete the first one (without this note). Thank you for your consideration.
Aldrin,
Your transforms for B-V and V-R for the SBIG STT 8300 camera with Baader RGB filters look quite different from mine using an SBIG ST-10me, also with Baader RGB filters.
I'm sending you my results to help with tracking down the problem.
For others interested in transforming tricolor RGB filters to standard magnitudes, I will only say here that my transforms for Green - Red to V-R IMO look pretty good. They are not very different from the ideal (color transform = 1, and Mag transfroms = 0). I expect good results when I get weather that allows me to test them by measuring some Landolt stars. All of my transforms for Blue- Green to B-V are far off base, and I'm currently not planning to test these.
Phil
Phil,
For your results that are 'pretty far off base', do you mean that the plots don't look good (e.g., large residuals for some observations)? Or do you mean that the values for the TCs are not what you expected?
Roy
Roy,
Your question makes a good point. Yes, the reason I'm not (currently) interested in pursuing the B-V transforms is partially that these transforms are not what I'm used to seeing, but it is more than just that.
When I look at the passbands for J/C BVR filters and the tricolor RGB filters from the same manufacturer the Green and V have the closest match. The Blue/B and Red/R passband matches are not as good, but I would be hard put to say which is better. In this case, all else being equal (e.g.SNR's for the standard stars) , I would expect the B-V transforms and the V-R transforms to differ from the ideal by roughly similar amounts.
Here are my transforms for the Baader RGB filters:
Tbv = 1.600 Tvr = 1.041
Tv_bv = -0.057 Tv_vr = -0.102
Tb_bv 0.325 Tr_vr = -0.047
This makes me think there may be something wrong with the B filter.
My main interest in calculating the transforms for the tricolor filters has been to see if the (Baader) Green to V transforms produce transformed V measurements as well as a standard J/C V filter. I think this is possible, but we may see after I measure some Landolt stars. It seems the transformed R measurements may also be reliable.
I'm not claiming that the Blue to B transforms won't work, but I may just leave that up to others to investigate.
Phil
Good day.
Here is the link to a folder containing screenshots of the transformation coefficients calculated with TG. https://drive.google.com/drive/folders/1jzJKJxjlX6pvTrUy2TZR3uoACn2tdz3F?usp=sharing
It seemed to reveal about the same values as with the spreadsheet method.
What do you think is the issue here? Did I miss anything important in the process?
Best regards,
Aldrin
Phil,
I think my question was unnecessary. Your post implies that you are concerned that your Blue-Green to B-V colour TCs do not approximate 1, and the mag transforms do not approach zero.
You've therefore decided not to use them. Why not do the experiment anyway?
If your transform plots are linear with small residuals, the transforms should work. After all, the formulae used to calculate transformed magnitudes can be derived algebraically from the formula (y = ax + b) that describes the transform plots. Therefore magnitude measurements on other standard stars should be accurate within the relevant error limits.
Roy
Roy,
Our messages crossed in the internet.
I see your point, but that can be true only if all the filters are doing their jobs properly. I think there is something wrong with the B filter (for photometric purposes).
Okay, I'll do at least one set of transformed B-V measurements of standard stars of various colors when I do the V-R observations. If the results are close to being accurate I'll do more for the statistics.
Phil
Phil,
If you have good transformation plots for your Blue filter with low residuals, and if it turned out that you could not get accurate B transforms after measuring other standard stars, that would be a complete mystery to me.
Let me know how you go.
Roy
Okay, Roy. I'll let you know.
Phil