Xilman

I'm a complete newbie so please forgive any solecisms. The last couple of days have been spent learning how to drive ASTAP and comparing the results with Laher's APT. APT has been my VS measuring workhorse for years because it is easy to script and easy to set up files containing the coordinates of objects to be measured; further comparison magnitudes can be taken directly from the AAVSO database. Comparing measurements of SS Cyg made by each program indicates comparable precision but with a noticeable...

Speeling misteak in 'readme how to compile.txt'

My point, prehaps badly phrased, is that DAOPHOT is an excellent search term for Google, DuckDuckGo, etc to learn about it if you haven't already come across the technique. A short while ago I downloaded a small piece of Python code which makes using the DAOPHOT algorithm very easy --- allegedly. I haven't yet played with it. Further detail at https://photutils.readthedocs.io/en/stable/psf.html FWIW, I am a retired computer-geek and amateur astronomer. Long ago learned to exploit the labours of ...

Some (most) of your questions will require more research than an instant answer can realistically provide. I will try to get back to you but I am suffering from a particularly bad cold at the moment (not covid, thankfully) so it may take a few days. In the meantime, I strongly recommend that you contact Russ Laher --- he is a very friendly and helpful guy --- about how he estimates the background in APT. Please feel free to mention my name (Paul Leyland) if you think it may help, or not if you don't....

han.k: you may already have examined how DAOPHOT does this. If not, the TL;DR is to fit a PSF, which could be either a simple Gaussian or an arbitrarily shaped "blob", to each detected star and then subtract that from the image; repeat until only background remains. Incidentally, this is a superb though computationally expensive algorithm for background estimation.

As noted, there are several background estimators in APT. That shown in the video is only one of them. I really don't know whether APT uses Sextractor (which I use myself, BTW) under the covers. Fairly sure that it doesn't call out to an external utility but it may well have re-implemented its algorithms. I should find out. Thanks for drawing it to my attention,

Doh! Aperture Photometry Tool

For a number of years I have been using Russ Laher's APT (A Photometry Tool) for VS photometry. It is a professional product written by a professional at Palomar for use by both amateurs professionals. Very highly recommended. APT implements elliptical apertures, designed for galaxy photometry but invaluable for measuring slightly trailed images. It also has superb sky background estimators --- several types to cater for different circumstances --- which are also easily configured. Not only that,...