PSFs of coadded images
- ORCID iD: 0000-0003-2271-1527
- ORCID iD: 0000-0002-4179-5175
- ORCID iD: 0000-0003-1666-0962
- ORCID iD: 0000-0003-2759-5764
- ORCID iD: 0000-0001-8783-6529
- ORCID iD: 0000-0002-5596-198X
Abstract
We provide a detailed exploration of the connection between choice of coaddition schemes and the point-spread function (PSF) of the resulting coadded images. In particular, we investigate what properties of the coaddition algorithm lead to the final coadded image having a well-defined PSF. The key elements of this discussion are as follows:
-
We provide an illustration of how linear coaddition schemes can produce a coadd that lacks a well-defined PSF even for relatively simple scenarios and choices of weight functions.
-
We provide a more formal demonstration of the fact that a linear coadd only has a well-defined PSF in the case that either (a) each input image has the same PSF or (b) the coadd is produced with weights that are independent of the signal.
-
We discuss some reasons that two plausible nonlinear coaddition algorithms (median and clipped-mean) fail to produce a consistent PSF profile for stars.
-
We demonstrate that all nonlinear coaddition procedures fail to produce a well-defined PSF for extended objects.
In the end, we conclude that, for any purpose where a well-defined PSF is desired, one should use a linear coaddition scheme with weights that do not correlate with the signal and are approximately uniform across typical objects of interest.