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AAVSO Transform Campaign

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WGR
WGR's picture
Color Coef vs Mag Coef

Hello George;

I have wondered the same thing.  I asked Arne once about this.  He said that in his experience, folks get better results using the magnitude (Tx_xy) coeficients, rather than the color coef (Txy).  In the magnitude coeficients, one is using 3 standard values and one instrumental value.  In the Color Coef, one is using two instrumental mags and 2 Standard Mags.  Presumable the former has less total error than the former, assuming that the Standard Values have lower errors than our instrumental mags.  Probably a good assumption.

When we apply our Transformation Coeficients in TA,  we don't have the Standard Values for the Variable, I believe we use the instrumental values to get the color term and assume that (b-v) = (B-V).  Is this correct?  I think you take the Submitted Mag, which is the (Target - Comp) + Standard Value of Comp and back out the Standard Value of the Comp and the Submitted Instrumental Mag of the Comp, the result being the Target instrumental mag.  Am I correct?

Gary

SGEO
SGEO's picture
Color coef vs Mag coef

" assuming that the Standard Values have lower errors than our instrumental mags.  Probably a good assumption".

Not so fast. The transformation process is all about computing the reference magnitudes for the variable star. So the error you compute for this reference mag must be greater than your instrumental error because it will pick up some of the error of the coefficients and other variable reference magnitudes in the transform group. 

Arne's point is valid: the magnitude coefficients only involve one variable magnitude instead of two, so might end up with a lower error. On the other hand, the magnitude coefficients for our amateur systems have larger errors than our color coefficients, so there is a trade off. So try both and compare the results. It's pretty easy with TA: run the transform process with the AAVSO recommended method and compare it to the Alternate method which use the color transforms.

There are two issues. The transform process pushes your observations to a model of the standard system. 1) Which is the better model? I submit that you want to conform to the best set of coefficients. 2) is the issue of the error propagation. Which method gives you the best error.

Note that both systems are valid. Transformation is not an exact process. Its goal is adjust your observations to the standard system as described by your coefficient set.

One way to test is to use TA's Test TC mechanism to see how well your model can compute the reference magnitudes of the check star. 

So I would suggest that if you are really pushing for best error value, try both methods. If one gives better values for the TestTC check, use it. If they are about equal, use the method that gives you the best error value.

 

Oh, in answer to your question about the process: Yes, TA starts with the guess that your variable reference magnitude is equal to your instrumental magnitude. Iteration through the equations then shifts that guess to a final reference magnitude. This is equivalent to solving the simultaneous equations.

George

 

WGR
WGR's picture
AAVSO vs Alternate Comparison

Hello George

I tried the experiment you suggested comparing methods.  Average Errors AAVSO/Alternate.  Pretty poor night.  Clouded over;  17 images in each band

B:   .007/.007

V:   .008/.025

I:    .006/014

 

Small sample of about 17 observations in each band.  I suspect that the B transformation is done with the same equations for AAVSO and Alternate.  I will check it out.  So it looks like the results are better for the AAVSO method, particularly in V and I.    R-squared values of the Transform Coef are plotted below.

R Squared Values

Tbv= 0.997
Tb_bv= 0.610
Tv_bv= 0.476
Tvr= 0.994
Tr_vr= 0.812
Tri= 0.982
Tr_ri= 0.676
Tvi= 0.985
Tv_vi= 0.561
 

Gary

HQA
HQA's picture
analysis parameters

Gary, remind me of your aperture radius (in arcsec, not pixels), your sky annulus radii, and your field of view for the M67 images used to make the TG plots.  Thanks!

Arne

WGR
WGR's picture
Aperture Dimensions

Hello Arne

The Aperture Radius was 8 arc secs, the Inner Radius was 16 arc secs and the Annulus Width was 16 arc seconds.  The fields of view was 14 arc minutes.  The FWHM was 2.6 to 3.3 arc seconds, depending on the band.

Gary

sgor
sgor's picture
Suspect Transformation Coefficients

Over the years I have oscilated between transforming and not transforming. With the emphasis on Transformation Coefficents, I generated coefficients from M67. I use a c14 with and ST10. Filters are BVRI from Astrodon. Following are the coefficients

#Tbv= 1.0340, +/- 0.0310
#Tvr= 1.3050, +/- 0.0760
#Tvi= 1.0170, +/- 0.0270
#Tri= 0.8090, +/- 0.0560
#Tb_bv= 0.0001, +/- 0.0330
#Tv_vr= -0.0750, +/- 0.0540
#Tv_vi= -0.0430, +/- 0.0300
#Tr_ri= -0.3690, +/- 0.0710
#Tv_bv= -0.0340, +/- 0.0270
#Tr_vr= -0.3080, +/- 0.0540
#Tr_vi= -0.1680, +/- 0.0310
#Ti_vi= -0.0600, +/- 0.0170

The Tb_bv was originally 0.0000 which caused TA to report that tall of the coefficints were missing. After some days of head scratching, i realized the problem and put in 0.0001. So question 1) is it likely that Tb_bv would be 0? Are other folks with similar camera and filters getting similar results?

Question 2) Do Tr_ri and Tr_vr seem suspicious?

I have data for BL Boo that I'm sitting on until I'm sure I can trust these coefficient. 

..george

SGEO
SGEO's picture
Suspect Transformation Coefficients

I was just looking at the issue in TA where I was treating a 0 value as a missing coefficient. 0 for a magnitude coefficient says your system is perfectly standard. I thought that would never happen in the real world. You proved me wrong. Good work- around setting it to 0.0001.

If you are wondering if your coefficient set is good, TA offers a reality check. Load up your BL Boo data and click the TCtest check box. It will apply your coefficients to your Check star data. Examine the report: Do your transformed values match the referenced data to a satisfying degree? Did the transformatoin process move your instrumental data closer to the reference?

George

Tonisee
M67 standard stars

Few years ago I used that old "boulders" M67 photometry file and found following stars to be good enough for creating transformation coefficients. My criteriae were: reasonably isolated stars, wide range of colors, and good SNR. My list was following (first column is RA and second is DEC):

132.799179 11.756206 M67-01
132.821344 11.804549 M67-02
132.845119 11.800557 M67-03
132.861935 11.811315 M67-04
132.802987 11.878504 M67-05
132.870902 11.842597 M67-06
132.931570 11.740761 M67-07
132.862659 11.864667 M67-10
132.885920 11.814540 M67-11
132.821106 11.846304 M67-12
132.860242 11.730831 M67-13
132.926626 11.856478 M67-14
132.840744 11.877244 M67-15
132.764746 11.750831 M67-16
132.937934 11.796177 M67-19
132.782656 11.802645 M67-20
132.926532 11.835538 M67-21
132.914222 11.862751 M67-24
132.913576 11.834474 M67-27
132.785038 11.786758 M67-29
132.927937 11.776905 M67-31
132.880267 11.764142 M67-37
132.789710 11.695902 M67-56

Maybe it's useful..

Best wishes,
Tõnis

MZK
MZK's picture
Transformation Coefficient Survey

Transformation Coefficient / Equipment Survey

Since many AAVSO members/photometrists are making efforts to generate transformation coefficients and use them to transform their observations, we thought that it would be interesting to tabulate these coefficients and attempt to determine if there are any relationships (statistical) among the values as it relates to: (1) the type of telescope (lens vs. mirror vs. hybrid), (2) the type of CCD (e.g., chip type or presence of microlens), and (3) the type of filter (e.g., glass vs. dielectric coating).

Therefore, we have generated a survey form at the following link:  http://goo.gl/forms/EEtKzK5kHZ
which we hope members will fill in and submit for evaluation. Our intent is to use this data to study the magnitude and differences in coefficients related to the parameters noted above. No personal information will be asked for or included in your responses. Some optional questions ask for a description (e.g., manufacturer /model) of your equipment (e.g., telescope, ccd or filter) but there is no requirement to provide it. It may be useful but the choice is yours.

We hope that you will participate in this survey. We plan to present the findings at a future AAVSO meeting. Most of the survey questions are simple choices from several alternatives. One question requires that you know what type of ccd chip (e.g., 6303, 3200 or other) you have. Your transformation coefficients will be tabulated so you will need to have a list of those coefficients (e.g., Tbv or Tv-bv) before opening the form. The TG *.ini file is a convenient place to gather this information.

We appreciate your participation in this survey.

George, Gordon and Ken

WGR
WGR's picture
Survey

Hello George, Gordon and Ken

Thanks for doing this.  I think it should be interesting.  

Would it be possible to just attach our .ini files, that way you would have all the information, including errors, rather than type it all in, and generate mistakes.  (I admit to being lazy).  

Gary

MZK
MZK's picture
Transformation Coefficient Survey

The Transformation Coefficient Survey has been a flop so far! I guess few observers are interested in spending a few minutes (literally less than 5 minutes) to provide the information and learn a little about how their systems compare with others.

We'll try once more. We have generated a survey form at the following link:  http://goo.gl/forms/EEtKzK5kHZ
which we hope members will fill in and submit for evaluation.

Ken

WGR
WGR's picture
New Forum

Hello Ken

If this does not work, I suggest that a new forum topic be started, with survey in the title.  It might work.  These forum sometimes take on a life of their own, but other seem to die.

Thanks for doing this.

 

Gary

JimSarge
JimSarge's picture
Transformation Coefficient Survey

Is there a way to see the current survey data?  I submitted the form and then later tried to go back to review the status of the data and couldn't find any way to see it.

Jim Seargeant

MZK
MZK's picture
Viewing Transform Coeff Survey Responses

Hi Jim, Brad and Gary:

YES, there are several ways to see google forms! However, I need to set it up and frankly I was embarrassed/disappointed in the number of responses so far. Of course, showing the results is an incentive for others to submit data. So, catch 22!   frown

First, I'll attach a pdf of the current data entry spreadsheet to this post. Expand it (zoom in) to see data since it's a wide spreadsheet. Subsequently, I'll set up / share google form summary sheets that are MUCH easier and interesting to look at. So keep the faith! You have reinvigorated mine with your response. smiley

Ken

 

FJQ
FJQ's picture
Viewing Transform Coeff Survey Responses

To:  Ken,

RE:"...frankly I was embarrassed/disappointed in the number of responses so far. "  I will respond to this as soon as I get back from Mt. Pinos on a pretty picture/photometry run.  I have at least 5-7 different transform coefficient sets from 2 cameras, 2 telescopes and 2 different sets of photometric and not so photometric filters.  From doing time series on AM Her, V404 Cyg,etc  I've submitted btw 1500 and 3000 transformed IVB magnitudes in the last 3 months.

James

spp
spp's picture
transform coefficient survey

Ken,

I just finish up with a new set of B-V and V-I transforms based on 36 stars in NCG 7790.   Are you still doing the survery?   If so, how do I send them to you?

Phil 

MZK
MZK's picture
Link to Transformation Coefficient Survey

Phil:

The following is the link to the survey to post transform coeffs.

https://docs.google.com/forms/d/13ZWdXto9DH_GVoUtBQ3pYgN5rEnMMiFdqWRKk35rqoo/viewform

I hope some others follow your lead?

Ken

 

CMJA
CMJA's picture
Link to Transformation Coefficient Survey

[quote=MZK]

Phil:

The following is the link to the survey to post transform coeffs.

https://docs.google.com/forms/d/13ZWdXto9DH_GVoUtBQ3pYgN5rEnMMiFdqWRKk35rqoo/viewform

I hope some others follow your lead?

Ken

 

[/quote]

Hi Ken,

Where are the results posted?

Michael

spp
spp's picture
transform survey

Ken,

Is there a way for us to view the results of the transforms survey?  If we can't get access directly, perhaps you could post the results so far.  I think a spreadsheet would be nice, but even a screen shot (as you posted in this form on May 21, '15) would be helpful

Phil

 

MZK
MZK's picture
Transform Survey

Phil:

I'll try to post something this weekend?

Ken

 

MZK
MZK's picture
Transformation Survey Results

Phil et al:

Attached is the current survey result in .xlsx format.  Still a small number of responders.  frown

If anyone wants to participate so we can learn more about the variation in coeffs and present them at a future meeting, the following link is provided. It takes 5 minutes if you have a copy of your coeffs and know specifics about your system before you log in.

https://docs.google.com/forms/d/13ZWdXto9DH_GVoUtBQ3pYgN5rEnMMiFdqWRKk35rqoo/viewform

 

Ken

spp
spp's picture
Transformation Survey Results

Thanks, Ken.  I'll ask the class members to enter their transforms in your survey.

Phil

WBY
WBY's picture
submitting coefficients

I'm working on it. It took me a long  time to get several nights of data on M67. Observing has really been hard in Texas because of the terrible spring weather. Even The Texas Star Party in the normally dry Davis Mountains in west Texas had clouds and rain most nights. The good news is that the almost constant clouds and frequent heavy rains are mitigating the terrible drought that much of Texas has experienced for the past 4 to 5 years. 

So bear with us a while longer.I am interested to see the response to Jim Seargeant's post concerning access to the transform survey results so we can compare our results with others. 

Brad Walter, WBY

 

SimonLowther
1st and 2nd Order Extinction Values?

Hi all,

It would appear that the CCD Manual and the transformation tools ignore the 1st and 2nd order extinction? Or more likely am I missing something?

Thanks Simon

SGEO
SGEO's picture
Extinction when transforming

Simon,

When transforming your observations with TA you can ignore 1st order extinction if your star and comp are at the same airmass; it mathematically cancels out.

TA will compute airmass for star and comp if you have provided observatory lat/long and then apply extinction if you have provided extinction coefficients. If so, try it with and without to measure the effect.

Secondary extinction is secondary, likely smaller than primary in effect. I'm looking in to adding this correction to TA in the future, but don't expect the value to out weigh the impact of final error increasing because of the added computation.

George

 

B.P.Vietje
B.P.Vietje's picture
Transforms vs Ensemble Measures ?

I'm pretty slow to the transforms discussion, and were it not for extensive input/help/hand-holding from Gordon Myers, I'd still be more or less completely clueless.

I understand that transforming our measurements allows for better direct comparison of data between observers and equipment setups, and should help reduce the spread of data from various observers.  The result should be more accurate data and cleaner light curves, no?

So I'm still left wondering which is "better":  transformed data from one comp and check star, or an ensemble measure with a larger number of comp's ?

My current understanding is that transforming our measurements leads to better accuracy, while ensemble measurements lead to higher precision and lower errors -- do I have it right?

I will appreciate any additional insights from anyone willing to help pound information through my thick skull!

Clear skies,

 

Brad Vietje, VBPA

Newbury, VT

spp
spp's picture
Ensembles and accuracy

 

Brad,

Actually, I think you could expect better accuracy by using ensembles when compared to using a single comp,  if the magnitudes were transformed in both cases.  It's not a matter of ensembles or transforms.  Ensemble measurements can also be transformed.

I believe precision is primarily a function of SNR and proper procedures-  good flats, good calibration methods, and proper photometry procedures.   But, suppose your nice, high SNR single comp star's magnitude had been poorly determined in the first place.  It this case, if your target also had a good SNR, you could have very good precision but poor accuracy.

With ensembles, some of the comp stars' "standard" magnitudes might be a little brighter, and some might be a little fainter than the "true" magnitude.  With muliple comps this, and other, systematic errors would tend to cancel out so the accuracy should be better.

I think that in some observing situations using a single comp star can be preferable to an ensemble.  This would be where the goal is for multiple observers to measure a time period or an absolute change in brightness, rather than  "accurate" magnitudes on the standard system.  In this case, having all the observers using the same "gold standard" comp is better, but also in this case, transformed magnitudes would make the combined data set better.

Phil 

SGEO
SGEO's picture
Transform vs Ensemble

Arne has weighed in on this topic:

"Ensemble photometry is very useful, as it not only averages out possible problems in your image, but also gives you a lot of diagnostic information.  However, if I had to choose between transforming my data with a single comparison star, or not transforming but using an ensemble, I'd definitely choose to transform."

The transform record in the AID will be more trusted by researchers for comparison with professional observations. If you use TA to do the transform there will be a detailed record in the comment section of the original data.

Transforming is the way the AAVSO wants to go.

George

spp
spp's picture
transform vs ensemble

George,

I thought I got in Brad's question the assumption that you can either use an ensemble or transform using a single comp star, but that you can't transform a measurement from an ensemble.   I'm just trying to make the point that that this is an unnecessary choice.   Whether you're using an ensemble or a single comp star, for the best accuracy both types of photometry should be transformed.

I've read that tranforming ensemble measurements is tricky, but doing this "with a click" is just another of the great advantages of using VPhot.

Phil

SGEO
SGEO's picture
Transform vs Ensembe

Phil,

Your poiint is well taken. VPhot is able to do ensemble + transform with the limitation that it only does 2 color transformations. So this is a valid route.

My TA program will not transform ensembles because the information about the ensemble (star names and instrumental mags) is not provided, only some average. My understanding of what should be submitted to AID is A) a good measure for the LCG and B) sufficient data in the record that a researcher can dig out the raw observation and refine it with updated comp star reference data. With the data submitted in the current design of the AAVSO Extended Format (AEF) record ensemble records do not provide sufficient data. Some enhancements have been made extending the length of the comment field of the AEF. TA uses this to provide full documentation of the transform process applied in using named subfields.. And I've been looking into putting details of the ensemble into this field too if I can identify a clean way to capture that data. Then TA might be able to transform 4 color ensembles.

Always more work to do!

George

 

WBY
WBY's picture
Transforming Ensembles

George, 

Transforming ensembles with TA came up a long time ago in one of the photometry topics related to transformation. I though the conclusion at which we arrived was that, while you cannot directly transform an ensemble in TA you could transform the target magnitude obtained using each individual comp star in the ensemble and then use a least squares fit to those individual values to arrive at the transformed value of the ensemble. 

You now have a zero point error (the standard deviation of the transformed target magnitudes obtained from the individual comps that is added in quadrature with the square route of the averaged variances (square of the TA error values) of the individual comp measurements:

SQRT(σ_zpt^2 + (σ_c1^2 + . . . + σ_cn^2)/n),

where σ_zpt^2 is the square of the standard deviation of the target magnitudes output from TA for individual comps and σ_c1^2 + . . . + σ_cn^2 is the sum of squares of the error values from TA for the target magnitude obtained from each of the individual comps, which are averaged by dividing by n.

So you can use TA but you have run it for each individual comp and then do a little more math, which is pretty easy in a spreadsheet. Please note that in the above calculation I have assumed that all comp measurements are given equal weight, which is the most common practice. 

The other Brad,

Brad Walter, WBY

 

By the way, why doesn't the symbol tool in the forum contain any Greek letters? I end up composing in Word and then transferring to the forum whenever I need Greek.

SGEO
SGEO's picture
Time to renew your transform coefficients!

M67 is moving into a convenient position in the evening sky and the Moon is clearing the scene. Time to take your shots of the M67 cluster!

 

The AAVSO's Transform Campaign was meant to be more than a one time event. It was meant to be a process change: The AAVSO wants data submitted to the AID to be transformed. Sure, transformation is not appropriate for some kinds of observations (like maybe high cadence CV and super novae timeseries),  but certainly for LPV's it is appropriate. And every year you should reassess your transform coefficients.

There are educational materials and software prepared to make it easy. See https://www.aavso.org/transform . All you need do now is take the images. You can generate a finder chart by putting in the star name EV Cnc into the VSP. Take the shots, calibrate them and push them into VPhot. The instructions will help you from there. Or ask for help; the Transform team is willing to walk you through the process. 

This call for M67 images applies to those who use the iTelescope network and AAVSOnet too. Everyone can and should transform!

Cheers

George

stellakafka
stellakafka's picture
your transformed data for a project!

Friends,

 

I have an additional request: as you acquire M67 data for the transformation campaign, could you please consider sending your images to me? I have a group of high school students who study variable stars in M67, and new data will add to the already existing dataset they are working with. Your help will be greatly appreciated.  

Thank you in advance for yoru time and consideration.

Best wishes - clear skies,

Stella.

MJB
MJB's picture
Help - no results - using maxim file

I am getting down to calculate transform values and while I get no error message I also get no results.  I am using a maxim generated file attached.  Any clues as to the problem most welcome.  Thanks.

PS not sure how I got .csv on the file name twice.  that does not seem to keep it from being read and if I remove one I get invalid file type error message. 

mgw
mgw's picture
File format

The file format doesn't look right. 

I'm tied up with grandkids right now - will look at this later tonight and send you suggestions.

Gordon

mgw
mgw's picture
Could you upload images to VPHOT and share with me?

Also,

Any chance you could upload your images to VPHOT and share with me - mgw

 

Gordo 

MJB
MJB's picture
NEVER MIND

GOT IT.  tHANKS. 

MJB
MJB's picture
Help interpreting results

The program generates a number of parameters that I do not understand and the manual does not elaborate on.  I have referred to some other publications about how the transformation process works.  From these I understand the primary outputs such as Tbv, etc.  However, I am not seeing any explanation of such items as Tb_bv and Tv_bv.  What are these about (translated to words) and what am I looking for in terms of results as I am selecting and deselecting data to be used in my final results?

 

Thanks. 

MJB
MJB's picture
Help interpreting results

The program generates a number of parameters that I do not understand and the manual does not elaborate on.  I have referred to some other publications about how the transformation process works.  From these I understand the primary outputs such as Tbv, etc.  However, I am not seeing any explanation of such items as Tb_bv and Tv_bv.  What are these about (translated to words) and what am I looking for in terms of results as I am selecting and deselecting data to be used in my final results?

 

Thanks. 

MJB
MJB's picture
VHOT file filter issue

PS it has been suggested that VHOT is easier but it takes an hour to upload the files and even though I used the wizard and it claimed the test pair loaded properly, the aggregate set are all labeled as B filter images when they are not.  And yes the fits header in each does reflect the filter used.  

I have the maxim thing working but might want to compare to vhot for down the road.  

 

MZK
MZK's picture
Multiple B Images

James (Bruce):

We have seen this filter name issue before. It is generally due to replicate file names and/or identical times?? If I recall correctly!?  ;-(

Could you share a few BVRI images with me at MZK? (Yes, I know they will all show as B.) Keep the faith! We can resolve this.

Ken

PS: We could also email/skype directly? That may be more efficient??

 

mgw
mgw's picture
Transform Explanations

Check out chapter 6 of the CCD Photometry Guide - it should answer most of your questions -

https://www.aavso.org/sites/default/files/publications_files/ccd_photometry_guide/PhotometryGuide-Chapter6.pdf

B.P.Vietje
B.P.Vietje's picture
New Transforms

Hi All,

 

I generated a new set of transform coefficients for the system at our observatory, which I will attempt to paste in, below.  Planewave CDK-17 with Apogee Alta U16M camera and Astrodon BVRI filters.  I have not used these to actually transform any measures yet, but they seem reasonable compared to other values I have seen.

I filled out Ken's survey, though I had to poke around quite a bit to find the link to it.  I'm also not certain of the micro-lensing question (KAF 16803).

Question 1:  Process for testing these with actual measures on known stars?  Do I measure a few well-characterized comp stars and transform the measures and see how close I get to standard measures?

Question 2:  (Related, but a little OT)  Its easy to find V and B-V data;  where can I access comp data in other wavelengths?

Clear skies,

 

Brad Vietje

Newbury, VT

MZK
MZK's picture
Your New Transforms

Brad:

Your new color coefficients look great! Nice and close to 1. The filter coeffs are perhaps a bit larger than ideal (0) BUT not terrible. Did you remove/deactivate the obvious outliers in TG? Perhaps you could attach an image of one or two of the filter coeff graphs for comment?  Thanks for using survey!

Q1: Yes, pretending some comps are targets and measuring transformed mags is a good procedure. Try to choose some comps with a wide range of color.

Q2: If you go to the vsp tool table and select additional filters/colors with the check boxes at the bottom of the page, then go back to the chart and click photometry table you will see other mags besides the default V and B-V.

Ken

PS: The ccd chips often have a small lens (microlens) over each pixel. Need to look at specs for your camera/chip. My search said yes.

B.P.Vietje
B.P.Vietje's picture
Thanks for your reply, Ken.

Thanks for your reply, Ken.

I did eliminate any outliers beyond the 3 sd limits.  Is there a way I can use TG (version 5.8) to review those plots and grab a screen shot without re-doing everything?  Sorry if that seems like a dumb question, but I only play with TG about twice a year, so I'm not that facile with it yet.  I suppose re-running these is no big deal, and I would not have to save the results, but there is some time invested in eliminating the outliers.  On my laptop (Win 8.1) I can zoom in to look at the clusters of tiny dots, but when I try to click on them, it zooms back out to the original scale (?), so it does take a little time.

As for the Rc and Ic comp data, I had NO idea it was that easy!  yes  I noticed a while back that all this information had seemingly dissappeared from the photometry tables, and wondered where it all had gone.  I've been manually adding the V and B-V values just to get at the B magnitudes -- DOH!  Foolish as that may seem, I'm betting I'm not the only one wink

Thanks for your expert help and advice, as always,

 

Brad

 

MZK
MZK's picture
TG Transforms

Brad:

TG V5.10 is the current version. It uses 2 SD instead of 3 SD now. (A subjective decision by 3 of us!) BTW, although some may object, it is not unreasonable to use a visual indication of outliers as well as the SD lines. Statistical indicators are just that, they are mathematical indicators of the quality of data but they are not necessarily perfect. They have some underlying assumptions about distribution of the data. Look for additional points that are "obvious" outliers from the trend line but do not get carried away!  This becomes a very subjective and therefore dangerous exercise but I bet you will improve the slope of the line and reduce the error.

Give it a try! Carefully watch what happens.

Ken

PS: Yes, you can retrieve old transform sets but not the graphs. If you know where you saved the instrumental mag files from VPhot (or other), it is quick to regenerate the graphs and remove outliers. Go further than the 3SD/2SD lines if visually "reasonable". See what happens.

 

B.P.Vietje
B.P.Vietje's picture
OK, I downloaded and

OK, I downloaded and installed TG 5.10.  I could not find any way to just copy the new file into the "Photometry Folder", as instructed, so I just started a new install.  I found the instructions didn't help with a Windows-64 install -- in fact, I could not find any photometry folder (MacOS?), and actually couldn't find TG listed anywhere under Windows programs (?)  Not sure how Windows recognises TG, but it doesn't seem to treat it as a "program".

Anyway, I re-ran the transforms with 5.10, and saved them, and saved images of each plot -- attached below, if all goes well.

Program (?) Notes:  I started with 5 images in each filter, and stacked these in MaxIm before uploading to Vphot, so I only have data from one stacked image from Vphot.  Importing these into TG 5.10, I end up with a single transform set.  I go to save the data, and while TG indicated it was saved, I have no idea where it is saved, or what the file is called. Failing to find them, I need to start TG again, recall them, then click the check box to average them (but there is only one set), and NOW I have the option to name the file and save it where I can later retrieve it.  By default, it is saved as an .ini file, which I can not upload or attach here...  I then have to retrieve the coefficients again, and try to save as a .txt file -- will this work?  Isn't there a better way to do this?!? -- VERY frustrating.

Nonetheless, if you, Gordon, or George could comment on the process and my results, I'll find that very helpful.  Perhaps you are collecting data on the difference in the process and eventual values with the newer version?  These new values are from the same images as those reported a few days ago with TG 5.8, so maybe useful to you, as well.

 

Thanks, and clear skies,

 

Brad Vietje, VBPA

Newbury, VT

mgw
mgw's picture
Saving the transforms in TG

Brad,

I'll update the user's guide to resolve your problem  - sorry. I see where its confusing.

When you click "Save Transform Set" on the first menu page it saves the transforms to an internal file - not a file that can be exported.  To use those files in creating a final tranform set for TA you must  first select "Review/Average Transform Sets", select from the file(s) you previously saved, average those you like most and then create an export file for TA. . 

(Note each transform set you create on the first menu is stamped with the observation JD and time you generated the transforms.  That's done because people often want to create multiple transform sets from one set of images but using different active stars. Other users want to create transform sets from images taken at different times/days.  Then as a final step they want to examine all the transform sets they have and combine a subset of them.)

Once you selected the set(s) you want to examine on the second menu, highlight the one(s) you want average and then export entering the file name.  TA requires the .ini file extension which is why it is the file type.

When you do the final save with the name you typed in, the message box shows the full file path and the .ini file name.  To print, navigate to the .ini file and double click - notepad willl open the ,ini file.  If that doesn't happen automatically, right click on the .ini file and select "Open with" and select notepad.

Sorry for the confusion.

Gordon

hjw
hjw's picture
M11 sequence?

Does anyone have a sequence already set for M11. I'm doing a new bvi transform set. Since there are well over 300 stars in the standard one and M11 is such knot of stars to work with. I thought someone might have a sequence already completed that they could share or send me.

mgw
mgw's picture
Let VPHOT identify the M11 standard stars

If you upload your images to VPHOT and select Catalogs -> Load AAVSO Standard Stars the identification will be done automatically.  Then download the photometry report and save.  Download one file for each image/filter.  Then use TG selecting all your downloaded files at once.  (Both VPHOT and TG work with M11).

 

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