manual photometry question
Stacking program, astrometric (plate) solver, fits file viewer
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han59
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Hi,
I have been doing photometry on the bright low amplitude variable kappa 2 Boo (4.50 - 4.58 mag). After running a manual star selection with five stars I can select the variable and a check star in the report form, but when selecting any comparison star from the list I get an error "Error reading comparison star magnitude. Could not find V= in ..." (see attachments). With the exception of one star all the chosen stars have a brightness annotation so I would think their magnitudes are known.
Did I do something wrong or did I overlook anything? Any help appreciated!
cs Axel
I assume the AAVSO database doesn't know these selected stars. They are then marked with their position only. Set the AAVSO annotation to maximum "Online database mag 99". After reopening one of the images again all your select stars should be annotated with AAVSO annotations. If not then your only option is the check mark comparison stars your database. See screenshot
I have loaded "Online database mag 99", selected stars marked with magnitudes and have redone the photometry. In the report I have first selected a check star and tried to select a comparison star but received the same "Error reading comparison star magnitude. Could not find V= in 141035.6+520237" message.
Anything else to try?
cs Axel
PS: Comparison/check star lists in the report form show only the coordinates which makes finding the right ones difficult, adding the magnitude would help.
In the image you should select besides the variable manually only green coloured (AAVSO) annotated stars as comparison stars. Does the image contain any green annotated star? Otherwise it can not retrieve the comparison magnitude from the AAVSO database.
Last edit: han.k 2025-06-01
Hi Han,
thanks for the explanation. There were no AAVSO annotated stars in the image so were did ASTAP get the magnitudes for the listed comparison stars that go into the ensemble?
cs Axel
If there are no AAVSO you must be targeting an unsual area. So you must activate as comparison the "ensemble local database V50"
https://sourceforge.net/p/astap-program/discussion/general/thread/bdc895874f/c4a6/attachment/Untitled.png
The program then calibrates against the stored Johnson-V magnitude value of all detected stars using the local database. So as a comparison an ensemble of (many) Gaia database stars.
cs Han
Kappa 2 Boo lies near the UMa border so it is just a 'normal' region - no idea why the AAVSO has no comparison stars in their data base. I will try your approach.
cs Axel
Can you attach one image to a post? I will have a look.
There is a screenshot attached on my first post. Or do you need an actual fits file?
I want to test it with an original file
Image taken with a 100/600 triplet lens and Nikon D5100 (APS-C)
There are two comparison stars:
https://apps.aavso.org/vsp/api/chart/?format=json&ra=213.558332&dec=51.649016&fov=164&maglimit=99
They are somehow not displayed....
Those two stars are outside the image. There is no AAVSO comparison star within the image.
Just had the AAVSO add a comparison star to the VSX. How often is the VSX file in ASTAP updated?
Yes that is the way. If you select "AAVSO anotation: online..." it is retrieved directly from the AAVSO VSX and VSP online database. The local database is maybe updated in 2 or 3 years.
It is already visible.
Very easy way to update the VSX data base! I ran a manual star selection with the variable and the new comparison star which worked ok, but the new star is shown three times in the check and comparison star lists (attachment). I guess that is not intended?
cs Axel
That happens if you click three times on the same star. You can place manually up to 10 circles on 10 stars to measure. After it is clicked three time it is also three time measured.
I will try to block this in the next version.
Do you have Johnson-V filter or just a green filter? Any Johnson-B filter?
Here have just RGB filters. I'm normally doing deepsky but I intend to automate the transformation from Blue and Red measurements to get a better TG value (from the green filter) compensated for for the colour difference (B-V values) between the var and comparison star.
Same if somebody has Johnson-B and Johnson-V. With transformation you can correct the measurement for the colour difference (B-V values) between the var and comparison star.
oops - didn't notice clicking so often! Preventing such a mistake is a good idea.
My images are only TG (DSLR). I just bought a CCD camera with a filter wheel but also only R/G/B-filters. Even a single Johnson filter at the required diameter for my camera is quite expensive.
Fixed in the version of today.