AAVSO Transform Campaign

American Association of Variable Star Observers (AAVSO)
Tue, 03/03/2015 - 05:14

Having multi-filter CCD observations transformed into the standard system is important: it makes our data cross-observer comparable and useful to the professional astronomers.

In 2014 we developed the tools to document and make this easier to do. Check out the documentation here.

And now M67, an excellent calibration target, is in the perfect position for evening observations.

What are you waiting for? Now is the time to move to the next level!

And there is help available: volunteers are listed below to help you learn each step of the process.

Goal of the campaign:
- Increase the number of observers who are submitting transformed data to WebObs.
    24 out of 134 observers submitted transformed observations in Jan-Feb 2015 
    Let's see if we can improve this metric!
- Use the tools developed this last year for transformation
   TG:  Transform Generator
   TA:  Transform Applier  version 2.30 or better  
--- Get those M67 images! Its a convenient evening target in the month of March.  Use best practice to get them BDF calibrated.
--- Extract the instrumental mags.
   VPHOT is the most convenient way to do this. It automatically identifies the standard stars in the field and TG is prepared to work with its output directly.
   Ken Menzies is available to help with questions: 
   If you use some other tool for extracting the mags then the issue will be using  the proper labels for the stars. AUID's are always preferred and are available
   with the photometry from VSP
--- Use TG to compute your transform coefficients
   Installation and process details are available here.   
   Gordon Myers is available to help with questions.  
   You can get your coefficients from TG in a format compatible with TA (INI file) when you save your results. 

--- Use TA to apply your transform your data
  - You prepare you WebObs submission as you already do. The only adjustments to that process:
      - Comp and Check stars should be identified by AUID. You may be able to use the  VSP labels, but AUID's are preferred.
      - The ChartID in your observation records needs to be a photometry page, not the picture chart.

  Installation and process details are avaiable at here.      
  - Get the latest version of TA here.           
  George Silvis is available to help with questions.  
  Before you start submitting TA transformed data, you should review the results. TA has a feature built in to help you. If you check "Test TC" the transform process will be applied to your Check Star data. Review the results in the Report tab. If your observations can reliably match the transformed standard magnitude of the Check star, then you can submit your variable star measurements with confidence.

--- Tell us how you're doing by posting comments to this thread. What needs to be changed to this process to make it easier? We'll fix it!






American Association of Variable Star Observers (AAVSO)
M11 Transform Coeffients

Here are my coeffients for M11 using the whole standard of comps (384) For BVI.

14" f/10 SCT and St-1001e Camera. Quite a load for VPHOT to process!

American Association of Variable Star Observers (AAVSO)
Newbie looking for feedback on transforms

As stated, I'm pretty new to photometry (but not to imaging).  I'm getting my feet wet by starting with generating my tranformations from images of NGC7790 from last summer, but the first number I'm getting for the color transform seems a bit high (don't really know if its reasonable):  T_bv = 1.308.  I've tried to follow the CCD manual as best as I can, and watched the CCD school video.  Details:

  • SBIG ST8XME on a C8 at f/10, with Chroma B and V filters
  • Stack of 3 images (averaged) in each filter (SNR(B)=88+/-2 (1sd), SNR(V)=132+/-1.5)
  • 35 stars in NGC7790 (uncrowded apertures), elimated outliers, R^2 for trendline = 0.996
  • Photometry using Muniwin, aperture diameter=11.8 pixels (aperture #7), inner annulus=15, outer=25 (average FWHM ~ 3.5 pixels or 3.3")
  • Transformed using a spreadsheet (for now)

Any feedback is appreciated, thanks.  I have more nights to analyze but don't expect a big difference since the plot looks pretty tight.


American Association of Variable Star Observers (AAVSO)
How to Transform and when?

George et al.,

I've been doing CCD photometry for about a year and a half now.  My measurements have been either on pulsating HADS stars or eclipsing binary systems.  I have submitted some of my measurements via WEBOBS, but have not been transforming my data.  I have B, V, Rc, and Ic filters, and have taken measurements of the standard cluster, M67, with all four filters on four separate nights.  On each night, I shot 10 images with each filter.  These were uploaded to VPhot, and the photometry results were downloaded and processed in Transform Generator.  I have the averaged coefficients, but am not sure what to do with them. 

While attending a webinar I learned that there is a Transform Applier function in VPhot.  I typically process my HADS, EB, or EW data offline using MPO Canopus, and do further analysis on the light curves with Period04, Peranso, and perhaps Binary Maker 3.  If my results are worth sharing, I usually produce an AAVSO format file in the PhotoRed page of MPO Canopus, and upload this through WEBOBS.  

I assume that using Transform Applier on the light curve data would require contemporanious measurements with multiple filters along with the transform coefficients.  For example, I could not use B-filter data from one night along with V-band values from another.  If I make measurements in repeated sequences of B, V, Rc, and Ic, will these be close enough in time?  If so, I could transform my data before submitting it.  Isn't this, however, a bit late in the process?  Wouldn't it be better to transform the data before I do the period phasing, Fourier analysis, etc.?  I suppose I just need help on the How To rather than on the Why To.


American Association of Variable Star Observers (AAVSO)
BVRI Time Series


Yes, the normal procedure is to image your target in a time series using repeated filter image sets (e.g., BVRIBVRI....). As a target pulsates or eclipses, its temperature/color will/may change over its period. Comparing different filter images from different phases on different days would certainly/likely not represent the same color/temperature! Transformation will correct your system's (filter/camera) magnitude for such color changes during the run. The image filter sets need to represent the same phase, so it makes sense to take them in a repeated series.

In VPhot you can run your time series with all filters in one step and generate the AAVSO Report. In the past, it was necessary to run each filter time series individually. This time series, multifilter report can then be imported in TA and run in one step. The transformed time series report is generated by TA and then you submit it to AAVSO. Note that TA requires one comp star, not an ensemble, to work properly. This is just a current reporting restriction of TA. LesvePhotometry can run a transformed, ensemble time series in one step.

I do not understand what you mean by "a bit late in the process'? The process is to collect your time series images, calculate your standard magnitudes by differential photometry, transform your magnitudes to correct for small differences between your system and the standard system, submit your data, and subsequently conduct any light curve analyses to calculate periods. In VPhot and other software, the differential photometry and transformation (i.e., standard magnitude color correction) may be done in one step or two steps. Light curve analysis can subsequently be conducted in period analysis software like VStar or Peranso or other.



Association Francaise des Observateurs d'Etoiles Variables (AFOEV)
Unable to use TA

I submit this report for transformation



#SOFTWARE=VPhot 4.0.35





FO Aqr,2460209.62666,13.572,0.014,V,NO,STD,ENSEMBLE,na,122,12.153,1.0805,0,X29253AO,|CMAGINS=-6.383|CREFMAG=13.265|ENSTYPE=1|KMAGINS=-7.495|KMAGSTD=12.153|KREFERR=0.046|KREFMAG=12.184|VMAGINS=-6.075

with this set of transformation coefficients

description= TG - Version 6.9a, Telescope= CDK 400, Time created (UT) = 2023_09_22_10:07:37
Tbv= -1.910
Tb_bv= 1.432
Tbr= -1.409
Tb_br= 0.931
Tv_bv= -0.045
Tvr= -0.944
Tv_vr= -0.170
Tr_vr= -2.161
Tbv= 0.162
Tb_bv= 0.054
Tbr= 0.045
Tb_br= 0.024
Tv_bv= 0.103
Tvr= 0.076
Tv_vr= 0.022
Tr_vr= 0.163
[R Squared Values]
Tbv= 0.983
Tb_bv= 0.997
Tbr= 0.999
Tb_br= 0.999
Tv_bv= 0.853
Tvr= 0.988
Tv_vr= 0.967
Tr_vr= 0.988

Image removed.


And I get this error message




#SOFTWARE=VPhot 4.0.35





FO Aqr,2460209.62666,13.572,0.014,V,NO,STD,ENSEMBLE,na,122,12.153,1.0805,0,X29253AO,|CMAGINS=-6.383|CREFMAG=13.265|ENSTYPE=1|KMAGINS=-7.495|KMAGSTD=12.153|KREFERR=0.046|KREFMAG=12.184|VMAGINS=-6.075

# Missing information; need Tv_bv and BVcolor.


Can anyone help me?

American Association of Variable Star Observers (AAVSO)
Help using TA

It looks like you have your transformation coefficients in the ini file, but have they
been loaded into your Telescope Profile? That's a necessary step for TA/VPhot to access them.

Because this is a single filter observation you will need to provide the estimated B-V color.

You're close!

American Association of Variable Star Observers (AAVSO)
Multiple filter images needed!


The normal transformation process requires images taken in 2 or more filters. Looks like you only used a single V filter? Do you only have one filter in your system?

With 2 or more filter images, the color of the target can be measured by TA. With only one filter image, it cannot be measured and you need to provide the color of the target in your aavso report. This single filter transformation is a more advanced procedure. If you look at the TA instructions, you should find what to do?

If you only have one filter, it is normal to submit untransformed data.