Parameterization of Outer-scale on DECam Point-spread Function

Abstract

Abstract A method to better parameterize the Outer-Scale (L 0) of the Point-Spread Function (PSF) in Dark Energy Camera is described. The PSF characterizes the atmospheric turbulence and diffraction in astronomical images. In particular, the Outer-Scale describes the maximum coherence length in the turbulent atmosphere and leads to a maximum value of the turbulence structure function. We model the PSF by computing a pattern of star features, which are used to fit our PSF model. For each star, we apply a weight function which maximizes the signal-to-noise ratio. We find difficulty in parameterizing L 0, thus, we propose to change the current Gaussian weight function to the von Kaŕmań weight function which extends to larger radii. We find that by changing to the von Kaŕmań, we double our total sensitivity but lose 1st order sensitivity to L 0. Therefore, ulterior methods need to be explored to parameterize L 0.