EQUINOX in header
Stacking program, astrometric (plate) solver, fits file viewer
Brought to you by:
han59
Menu
▾
▴
I have been successfully processing my variable star images using ASTAP and submitting them to AAVSO. However, I wanted to try using the AAVSO VPhot program to see how well it's photometry matched ASTAP.
However, when I would try to upload images to VPhot, it would silently reject them. Someone on the VPhot forum suggested adding EQUINOX = 2000 to the header. After doing so, VPhot accepted it.
Is this something ASTAP could automatically add to the header? Currently, I just typed it into the head display and hit "Save new header". This works but it would be nice if it were automated somewhat.
I'm a little surprised that ASIAir doesn't add this since it is doing the initial plate solve. Does the FITS specification dictate that the RA/Dec be in J2000 so this is not needed? If so, why does VPhot choke if it is not there?
EQUINOX = 2000.0 is standard added to the header. Strange. Do you still have the original file for investigation?
You can add any keyword to the header in the stackmenu. In one of the tabs, select the files involved, the just press the right mouse button and select in the popup menu and select "Change keywords in selected files" then enter equinox and then 2000.
Tell me the differences between VPHOT and ASTAP. That is interesting.
Han
Last edit: han.k 2022-02-11
Here is an example:
https://www.otherwise.com/ASTAP/Light_NGC2392_30.0s_Bin1_20220207-201423_0001.fit
This was created by ASIAir. There is no EQUINOX there. If I open the image in ASTAP and do a Plave Solve and save the new header, there is still no EQUINOX.
I'm not sure I've used either ASTAP or VPhot to give a good comparison. VPhot has a lot more options for configuring the measurement. You can examine and choose which comp stars would be best for the photometry.
There are better options for placement and sizing of the aperture and sky annulus.
I also like the display in VPhot. Often in ASTAP it is hard to read the labels on stars as they are overlayed with other labels and when you zoom out thy are almost unreadable. I've attached an image of what VPhot shows.
Right now I'm leaning towards doing all the calibration, green extraction, and stacking in ASTAP and then switch to VPhot for the actual photometry.
One disadvantage of VPhot is that when you upload images, they sit in a queue for initial processing. In the morning, when everone is submitting data, it can take 30 minutes or so for you images to get processed so you can start photometry.
Hello Bill,
In ASTAP version 2022-2-12, the equinox is always added to the header.
If VPhot works better for you use VPhot. No problem.
If you find any other problem or bug or performance news please give feedback. Feedback help to make ASTAP better.
Han
From your download page it looks like only the Windows versions are at 2022-2-12. I am on macOS. Will you be releasing a build for that soon?
In a few hours. :)