If the object is a perfect 2D gaussian point source, the aperture size does not matter. Or, if you are certain about the location of centroid, you can fix it and the centroid would not be a choice variable. Also, you might want to specify how large the search area should be given the initially specified spot. Fixing is to do the centroid search by using averages given some sizes of the areas. Then, the routine will choose a centroid, mu, and variance (or mus and variances).Ī couple of things that will complicate the routine. First, you pick the PSF function, which is a 2D gaussian in this case. The image is 2D pixels, the PSF fitting routine would do something like this. So I'd like to better understand - how exactly does one find the flux of an object by fitting it to a PSF? And how should that PSF be normalized? I'm not sure what's happening behind the scenes here (I got lost in the documentation), and I'm not sure if I can trust any of these flux values, considering the x_0 and y_0 are always off. But when I change this normalization so that the total flux (sum of all the pixels) is 1, the result for the flux after fitting I get is way higher. Also, to get this result, the PSF data was normalized so that the max intensity point is 1. The correct coordinates are around (300, 300). However, these are not the correct centroid coordinates of the source in the image. Print(np.median(img), np.max(img), np.sum(img)) I have tried something simpler below (where model_data is the 2d numpy array representation of the PSF, and img is the asteroid image data): import numpy as np Furthermore, when I tried using this package, I wasn't getting any outputs anyway (it said a source was found, but that it didn't meet the sharpness or roundness criteria, despite me changing those parameters around quite a bit). I know that astropy offers a package called photutils.psf which does the PSF fitting for you, but I would like to better understand what's going on behind the fitting, and how the flux of the source is resolved from it. I've only recently begun studying PSFs, so I am a bit confused. I have an image of a single unsaturated source (asteroid) that I'd like to fit guesses for various model PSFs to, so that I can then compare the total flux in each case.

Python 2d fitting