Calibration None in Photometry tab

[Aleh]

Hi.
When I load a set of images on the Lights tab and then calibrate and align them, I see on the Results tab in the Calibration column “DBF” which means my images are calibrated. But after moving the files from the Result tab to the Photometry tab, all the files have a value of None in the Calibration column. Perhaps it happens because the CALSTAT variable is not written in the file header, although the number of calibration files and their type are specified correctly.
Thank you.

[han.k]

Thanks for the feedback. I will check

[han.k]

Strange. It works here. Can you recheck? Note the the "DFB"only becomes visible if you press analyse in the photmetry tab.. The analysed values are not copied. Only the file name.

Note you can also calibrate directly from the photometry tab using the popup menu. But what you described should be fixed it it doesn't work.

Han

[Aleh]

I load some lights (fig.1) Then I analyzed them. "Calibration" column is empty. I press "Calibration and Alignment only". Files in the "Result" tab have "DFB" in column "Calibration" (fig.2) Then I select all and use "Copy selected images to tab Photometry". Ok, now I see all files in Photometry tab. But column Calibration is "None" now. And it still "None" after Analyse button and even after Analyse + button (fig.3)

[han.k]

I see it happening for calibration & alignment. So your files end with _alignment.

I will fix that.

For photometry your should use the option calibration only. Then the file names are extended with _cal. With calibration& alignment you could potentially get photometric errors because it has to rotate/shift the image and pixels will be shifted & moved. Pixels will be combined or even worse when a pixel position is jumped over it it will be filled later to avoid black spots.

Han

[han.k]

Will be fixed in ASTAP version 2024.02.28 and available in 15 minutes.

[Aleh]

Thank you for the clarification.
Yes, for precision photometry, when absolute value is important, alignment distorts the reading. But if I want to get exactly the brightness curve, for example when looking for the minimum of an eclipsing variable or the transit of an exoplanet, then using alignment allows me to get a much better signal-to-noise value and reduce the scatter.

[han.k]

The photometry tab will keep track of the object based on the ra,dec position. Any large drift will be handled. After the photometric measurement the image will be aligned and displayed aligned. If you use ASTAP then do just calibrate only.

Success, Han

[han.k]

You can also stack in groups of two, four images. See popup menu photometry tab. That is still alignment but it could help for faint objects.

[Aleh]

I was wondering if there isn't a way to “take” the stars from each shot (different parameters of them), then stack the background from all the shots and use that for the saved stars? It seems to me that this would greatly improve the signal to noise ratio and get useful data in the low value region?

[han.k]

Please upgrade to ASTAP version 2025.03.07. The previous versions have a bug in sigma clip stacking of OSC images.

Cheers, Han