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Offset between IRAF and DAOPhotPSFPhotometry

See original GitHub issue

(I’m sorry for flooding the issues with questions. Please let me know if I should give it a rest)

I’m testing the DAOPhotPSFPhotometry class against IRAF’s usual tasks for CCD PSF photometry.

Given an observed frame I first run the IRAF tasks:

detect sources (daofind)
aperture photometry on the sources (phot) to use as initial estimates of the fluxes
creation of the PSF model (nstar , substar , psf)
PSF-fitting (allstar)

I then use the same list of sources (the ones found by daofind) to perform PSF fitting with DAOPhotPSFPhotometry using as psf_model an IntegratedGaussianPRF. I obtain magnitudes using the same zero point and exposure time as done with IRAF. I run this process twice: first fixing the coordinates of the sources in the psf_model, and then fitting them.

What I find is an offset between the differences of the final magnitudes obtained with IRAF and DAOPhotPSFPhotometry in both cases: a ~0.07 overestimation by photutils when using the fixed sources, and a ~0.02 underestimation when the sources are also fitted (the sources are sorted and matched before obtaining the differences).

figure_1

The scatter between the IRAF and photutils magnitudes is understandable, but I don’t know what parameter(s) is(are) responsible for causing these offsets.

Issue Analytics

State:
Created 6 years ago
Comments:5 (5 by maintainers)

Top GitHub Comments

1reaction

eteqcommented, Dec 5, 2017

Oh and re:

I’m sorry for flooding the issues with questions. Please let me know if I should give it a rest

Some of these are quite reasonable feature requests or possible issues (e.g. #620, #626). But in generally when you have a question (rather than a specific problem like “this doesn’t work” or “this should be added”) you’ll have better luck trying an environment like the facebook group, the astropy mailing list, or the astropy slack channel (e.g. http://www.astropy.org/help.html).

Admittedly, some are ambiguous - like this particular one might be a code issue, so it’s reasonable to ask here, and it might end up getting closed if it turns out there’s not a code issue to be addressed.

0reactions

Gabriel-pcommented, Jan 20, 2018

@mirca I have zero time right now but as soon as I can I’ll re-do the test paying attention to this kind of details. Sorry I can’t help more at the time.

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