Picking Check and "3" water for photometry
Stacking program, astrometric (plate) solver, fits file viewer
Brought to you by:
han59
Menu
▾
▴
[Sorry for the confusing title. the word "water" is supposed to be "stars"]
I'm a bit confused about how you pick the "3" and Check stars for photometry for submission to AAVSO.
I was doing photometry on R Gem. I had picked Check and "3" stars as shown in my atttached image. However, when I went to submit, I needed to know the name of the Check star. I right clicked on it and did a SIMBAD query. It came back with this being the variable star TW Gem.
In the Stack Menu I had requested it annotate variables. I assume this was what the gren labels were. But obviously TW Gem was not marked and I mistakingly chose it for the Check star.
I guess I don't understand how one is supposed to pick these. Surely I don't need to confer with SIMBAD to varify it is not a variable. What is the process I'm suposed to follow.
Last edit: Bill Tschumy 2022-02-08
Hello Bill,
Yellow annotated stars are variable. The green annotated stars are the official check stars. So best way is the use one of the green annotated stars as check star.
000-BBM-542
or
000-BKD-970
or
000-BKD-966
Probably 000-BKD-966 would be a good one since it magnitude in Johnson-V is 9.248 (all in the annotation) You have to enter the check star identification manually in the report.
Star 3 is just extra. Not required.
The reference stars are all detected gaia stars. You have to use the V17 database since it contains Johnson-V magnitudes.
Unter the viewer popup menu, Online query there are two AAVSO options
Ask any other question.
Han
Why wasn't the star TW Gem annotated in yellow? Presumably ASTAP is aware of all the variable stars so it doesn't use them for comparison.
If you choose a check star, what is the best way to get its name for the AAVSO? In the AAVSO Report panel there is a popup for the Name Check Star. It has 070830.1+225128 in it. Thats looks like the raw RA/Dec for the star. Is that suficient?
I'm also a bit confused by the names in the green designations (e.g. 000-BBM-542 ). I'm not familiar with that designation either. What is it?
Not all variable stars are included. I created a sub selection of the brightest one. TW GEM has no documented period, so that is probably the reason I skipped it.
AAVSO prefers the use the AUID designations. So something like 000-BKD-966. That is there internal designation for check stars. See attached plot and table. The ra, dec position is only to be used if no AUID star is available.
Han
I was looking back over this thread and had a question. As you know from another thread I am submitting TG observations by extracting the Green channel and working with that.
You commented that the V17 database contains the Johnson-V magnitudes. Does it also contain magnitudes at other wavelengths? I would think you would want to use a database that has TG values, otherwise the comparison stars (Johnson-V) will not be equivalent.
How are you supposed to to do photometry at different wavelengths if the comp database is all V?
TG is a little depended on the sensor manufacture. The recomendation is to use Johnson-V values for comparison.
The V17 also contains the difference between Gaia blue and red. These values are only used for colouring the annotation or star in my planetarium program.
That is not implemented yet. I have also to study the AAVSO guidelines if there is a standard for that. At the moment I simple don't know. Second problem is that for blue and red you are using only one in four pixels of your camera. For green is that two in four. So a DSLR/OSC camera is less suited for red and blue photometry.
OK, so hopefully the V band is close enough when measuring TG.
If I eventually get a dedicated astro camera and shoot though standard filters, will I have to abandon ASTAP? If the image is Johnson-B can ASTAP reasonably measure it with a Johnson-V database?
For Johnson-B, I have to create a Johnson-B database. Not a problem, the formulas for Gaia star database are available. Something for the future :)