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Astronomy

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    $\begingroup$ If you're looking for the total flux of the system, just draw a box around your image and add up the pixel values for every pixel in your box. That's all flux is. $\endgroup$
    – zephyr
    Commented Sep 21, 2018 at 14:36
  • $\begingroup$ @zephyr Yes, but how is this accomplished by fitting a PSF to the image? $\endgroup$
    – curious_cosmo
    Commented Sep 21, 2018 at 16:41
  • $\begingroup$ As Carl Witthoft answered, it doesn't make sense to apply a PSF to an extended source. Besides, even if this was a star, you wouldn't calculate flux by fitting a PSF to it first. You'd do exactly what I said and draw a box around your object and add up the values of the pixels in that box (although you can use the PSF to inform what your box should be for a point object). $\endgroup$
    – zephyr
    Commented Sep 21, 2018 at 17:41
  • $\begingroup$ When you say draw a box around the object, how does one choose the correct size of box? With a nonzero background and noise in the image, a bigger box would increase the flux even though the source doesn't extend further into the bigger box. $\endgroup$
    – curious_cosmo
    Commented Sep 21, 2018 at 17:56
  • $\begingroup$ Also, sorry but how is an asteroid an extended source? (this term was unfamiliar to me until I looked it up just now) Wouldn't the angular size of an asteroid imaged by WISE be less than the telescope resolution, classifying it as a point source? $\endgroup$
    – curious_cosmo
    Commented Sep 21, 2018 at 18:00