Andy Howell

It works beautifully now, even with a smaller 2.0 (xHFD) aperture! All 58 stacked images give 58 magnitude values and a nice-looking light curve. (attached) My faith is renewed, and I am most grateful. I must remember to disable star autocenter in cases like this, and to inspect images more carefully. Thank you, Han! Best, Andy

Pixinsight uses bilinear interpolation to fill in the missing TG values at TB and TR pixels. Separately, I have sent you a link to the ASTAP stacked images used for the ASTAP photometry. Thank you!

The graph that shows TG extracted using ASTAP

I did a test where I extracted TG using Pixinsight, which generates full-size (1x1 binned) images. Then I did the same using ASTAP, which generates half-size (2x2 binned) images. After TG extraction, the FITS files in each of the two sets of images were stacked in groups of ten. ASTAP successfully did photometry on almost 80% (46/58) of the full-size images, but just 31% (18/58) of the half-size images. The telescope was a Seestar S30 Pro. Part of the issue is that images were perfectly focused.

I use an Intel-based Mac. To select files for upload, I click ASTAP's Browse button at the Photometry tab, followed by "Edit > Select All" from ASTAP's menu. To select everything in a long list of files, I have to repeat "Edit > Select All" one more time to ensure that all files in the list are selected. This seems to be a quirk in the Mac OS operating system. I hope my method works for you.

Hello Han, the annulus setting (ASTAP version 2026.10.08, Intel 64 bit) in the Photometry tab has a drop-down menu with settings that range from 20px to 60px. I am not clear how to pick the correct setting. I am a little confused because I was accustomed to seeing annulus expressed as a multiple of stellar HFD. Thanks in advance for the clarification. Best, Andy

Hello Han, Follow-up. "Star Alignment" not "Astrometric Alignment" in the alignment tab seems to do the trick. The images now match on stars while ignoring foreground objects. (image attached) Not sure why I did not find this before. Furthermore, photometry appears to work well on the stacked image, despite presence of the foreground object. This will be a huge time-saver. Thank you again.

Hello Han, Yes, ASTAP stacking in groups works great when the field does not have distractors in the foreground - e.g., side of my house. When there are distractors in the foreground, they confuse ASTAP because it places extraneous quadrilaterals that match highlights that are part of the house, not the sky. Not surprisingly, the resulting image looks confused (attached). I was hoping there might be a way of supressing star matching altogether. Probably I need to find another way - e.g., cropping...