Sat, 06/17/2023 - 18:35
I'm relatively new to AAVSO and wanted to validate my TCs. I read the post where there is a new feature in Vphot that will created the requisite fields so that you can us the TA app (with the test coefficients box checked) to validate your coefficients if you used the Ensemble approach. But, when I generate a files from VPhot they don't have the "C" mag values. I must be missing something simple.
The contents of the report is:
#TYPE=EXTENDED
#OBSCODE=SJMJ
#SOFTWARE=VPhot 4.0.34
#DELIM=,
#DATE=JD
#OBSTYPE=CCD
#NAME,DATE,MAG,MERR,FILT,TRANS,MTYPE,CNAME,CMAG,KNAME,KMAG,AMASS,GROUP,CHART,NOTES
XX Oph,2460112.78932,9.092,0.075,V,NO,STD,ENSEMBLE,na,NSV 9567,10.247,1.2787,na,X28651AGN,|KMAG=10.247|KMAGINS=-7.945|KREFMAG=0.000|VMAGINS=-9.099
John:
1. Did you look at the help paragraph about 'test coefficients' at the bottom of the help page for TransformApplier?
2. Is this what you expected to accomplish? Not sure why your check star is NSV9567? KREFMAG=0.000?
Ken
The help page says that TA cannot be used with Ensemble to validate coefficients but this post
https://www.aavso.org/vphot-update-includes-transformation-ensembles
seems to indicate that Vphot will produce a file that can go into TA. that is what generated my initial question.
Sorry to be a bit block headed on this. My actual issue is how can I validate that my TC's are correct. I did do a non ensemble TA and got an error of .021 but thought that the ensemble approach might generate a more accurate result.
John,
Formerly, TA did not work with ensembles. Last March a new version of TA which does work with ensembles was added to VPhot. It looks like the TA Help document hasn't yet been updated to reflect this.
"I did do a non ensemble TA and got an error of .021 but thought that the ensemble approach might generate a more accurate result."
We normally consider the Error estimate as a measure of precision, not accuracy. If you used a single image and a single comp star your VPhot Err would just be the inverse of the SNR of the target, not a very reliable estimate. Accuracy is a different (but related) discussion.
"...how can I validate that my TC's are correct."
Make transformed measurements of Landolt standard stars. Comparing your magnitude estimates vs Landolt's (especially for red Landolt stars) would be a way to evaluate your over-all photometric accuracy, including your transform coefficients.
Phil
I will definitely try the measurement of the Landolt's stars. But, just to be clear about what I was quoting in the error estimate. The .021 was the calculated err of the TCs (based on the TA being used with the check box that produces an error value for your TC's. I thought that that was the actual err of the TC using the measured filters. Is that not so? Trying to understand exactly what the err value is when you use TA to measure the err of the TC's. Thanks for all the help.
TA Coeff Test Procedure (duplicate from another forum post)
John:
1. Now that I understand where your aavso reports came from, I think I understand what you did (or did not do)?
2. To conduct a TA Transform Coeff Test, you need to be running an aavso report(s) that includes data from a set of images that include at least two filters. That is the way TA works normally. It appears from your report that you were only using an aavso report from V filters? Have you previously successfully run a normal TA transformation of some of your data?
3. The Coeff Test box assumes that you are running a 'normal' transformation of a non-transform aavso photometry report BUT it exchanges the check star for the target.
4. In so doing, TA Coeff Test adds a line to the report output that reports the transformed magnitude of the check star that is listed with its AUID name.
5. The report in the bottom box of the TA page, reports the difference between the transformed magnitude of the check star and its known magnitude.
6. In my test, my transform coeffs yielded an agreement of 0.003 mag for my Check star. BTW, the Coeff Test does still appear to require only one comp to provide reasonable transformed mags of the check star.
Hopefully, this makes sense?
Ken
Yes, that clarifies it for me. I'll go back and rerun and see what happens. BTW, I didn't see an explanation in the help file as to what is actually reported in the Test TC optional reporting line.
"3. The Coeff Test box assumes that you are running a 'normal' transformation of a non-transform aavso photometry report BUT it exchanges the check star for the target.
4. In so doing, TA Coeff Test adds a line to the report output that reports the transformed magnitude of the check star that is listed with its AUID name."
Perhaps I misunderstand, but does this mean that if you run VPHOT to yield transformed magnitudes of the variable, the report will _not_ by default include the transformed magnitude of the check star?
Roy
I'll let Ken give the definitive answer but I believe this is only true if you request the TA Coeff Test with the check box, something that you normally wouldn't do in the course of day to day transformational work.
Roy:
1. If you run 2 color transformation in VPhot, both the target and the check are reported as transformed standard magnitudes in the AEFF Report. You can prove this to yourself by reviewing the Color Photometry Report page and the AEFF report.
2. If you run TransformApplier in VPhot, the target magnitude is reported as transformed magnitude in the AEFF Report but the check magnitude is reported as the non-transformed magnitude in the same AEFF report.
Run one of your sets of multi-color images in VPhot/TA and see what the TA AEFF report indicates in the non-transformed line versus the transformed line? Use an ensemble since that reports standard mag rather than instrumental mag for the check.
Ken
That…
Thanks Ken and John,
That makes sense. Ken, I may not get around to doing what you suggest (sorry). I'm not actually using VPHOT (I'd need to do a big refresher of material from your VPHOT CHOICE course), and all my images are now through a V filter for the timing of EB minima from non-transformed magnitudes.
Roy