Point spread function (PSF) modeling

PSF modeling characterizes the shape of point sources after they have been “blurred” by the atmosphere and optical system into a two-dimensional shape on the detector.

PSF modeling uses the Piff (Jarvis et al. 2021) algorithm.

Overview

Bright, isolated stars are detected in post-ISR images and used for PSF modeling.

The Piff models represent the PSF on a pixel-by-pixel basis and interpolate its parameters across a single CCD using two-dimensional polynomials. Piff utilizes its pixel grid model with a fourth-order polynomial interpolation per CCD, except in the u-band, where star counts are insufficient to support a fourth-order fit. In this case, a second-order polynomial is used instead.