I am using Vphot for stars in SNEWS campaign. When running a Transform Applier report I get the error:
VSX returned invalid data: [json.exception.parse_error.101] parse error at line 1, column 1: syntax error while parsing value - invalid literal; last read: ‘<’ target not in VSX. Missing information; need Ti_vi and VIcolor.
In the details files:
Star Date Filter Grp Vstd Vins Vex Vtran diff VERR VERRt
"V0509 Cas " 2460865.901331 I 0101 4.212 -13.052 4.212 not transformed
Stack BBB makes sense
I am guessing that you are staking Bs, stacking Is, stacking Vs and running time series on all of them at the same time? that would make sense to me.
The json errors are known and being worked on as far as I know. I also get them but they do not hinder my data reporting from TA.
I do watch that the correct number of datapoints are reported and that they are all transformed. That is relatively easy because we have the image counter in VPHOT and another image counter in the Old WebOBS. Also old WebOBS and now new WebOBS have the transformed status column that says YES/NO. The Old WebOBS has the additional benefit of displaying the input in one scrollable screen rather than ten at a time. That makes scanning 300 entries palatable.
Obviously if we had a solution for this unfortunately intermittent problem, we’d all be happy. but that is not the case.
IMHO, reporting your untransformed results is a reasonable if not ideal option. You can save your normal time series photometry report from vphot and run it through TA in the future and edit the previous data if desired.
BTW, if you are only running a pair of filter images you could use the 2-color transform tool.
The normal initial photometry process would be to run your images through a VPhot time series and create and save the untransformed result file (AEFF format). Then you don’t need to worry about your images being lost. You could choose to submit those untransformed results as desired. When TA is running properly again, you can update the results if desired by using this AEFF report as normal in TA.
If you actually have a single image (single or stacked) in multiple filters, you can try the 2-color transform tool in VPhot and avoid the TA problem. Do you understand how to do this?
Thanks Ken, I did try your first suggestion, the two colour transform but it returned very odd magnitudes so I clearly don’t know how to use it. As stated on other post. I ran it on some six stars an hour or so ago and everything worked fine.
You have 3 different filters. How many different pairs of filters can you make? There are not many! Try all of the possible pairs and see what your results are?
Transformation converts instrumental magnitudes, obtained by telescope and a camera, into a standard system that allows data to be compared and combined among the wide scientific community.
I tried to do 2-color transform with images:
Stacked B-I and I got the message:
Transform coefficient:
TBI = 1.015 TI = missing
At least one of the transformation coefficients has not been set for this filter combination.
For what I read in the support pages in AAVSO, it seems that the telescope user needs to calculate this coefficient.
Is this something I could obtained/calculate and enter in the report?
Since I don’t have much experience with VPhot or transformations, I’ll let others answer your main question. However, since you mentioned you’re working on the SNEWS campaign… are you using the images from AAVSOnet, by any chance? If so, then I believe that the AAVSOnet volunteers have already computed accurate transformation coefficients which you can use. I’m not sure where they are posted, but @MZK is the System Technical Advisor so I bet that he can point you in the right direction.
[FYI, I made a small edit to your latest post: converting the quotes into Discourse’s dynamic quote formatting, which is made by highlighting text and clicking the “quote” button which pops up. Just mentioning in case you notice that it looks different!]
Have a think about your answer to the question “What are you trying to correct for with transformation?” after you look at the following formula. It converts instrumental magnitudes to a standard magnitude. The example below relates to data through a Johnson V filter:
V-target = V-comp + (v-target - v-comp)
V refers to standard magnitude (calculated for the target, from a catalogue for the comp)
v refers to instrumental magnitude
The point to note is that the formula does not include any transformation coefficient.
There are lots of steps!
VPHOT generally works pretty well.
Remember to display one of your images before you do the transform thing. (No one knows why!)
Sounds like you have mostly gone through these steps but it doesn’t hurt to complete all the steps to learn how.
Have you stepped through the VPHOT manual? If not, you should literally step through it. It is the How-to guide:
Then to transform:
Click TransformApplier in the middle of the list above your images.
Select the telescope from the list of mostly AAVSOnet telescopes. When you do that you get the transforms for that telescope so that your transformations will be correct. You will see the AAVSOnet telescope that took those images in the image headers that can be displayed with the Fits Header button at top right of a displayed image. The image descriptions on the VPHOT front page image list also tell you which AAVSOnet telescope gathered the image.
Load the photometry file that you saved.
Create Transformed Output and save it where yo can find it with WebOBS.
That file gets uploaded to WebOBS.
That is the final step. Then you can go look how well you did with LCG or VSTAR.
