Filter-substrate refraction causes dominant lateral shifts yielding 0.3-0.4% PSF size and ellipticity residuals across most Roman bands that exceed weak lensing requirements by an order of magnitude, while longitudinal defocus shifts remain negligible.
Chromatic CCD effects on weak lensing measurements for LSST
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abstract
Wavelength-dependent point spread functions (PSFs) violate an implicit assumption in current galaxy shape measurement algorithms that deconvolve the PSF measured from stars (which have stellar spectral energy distributions (SEDs)) from images of galaxies (which have galactic SEDs). Since the absorption length of silicon depends on wavelength, CCDs are a potential source of PSF chromaticity. Here we develop two toy models to estimate the sensitivity of the cosmic shear survey from the Large Synoptic Survey Telescope to chromatic effects in CCDs. We then compare these toy models to simulated estimates of PSF chromaticity derived from the LSST photon simulator PhoSim. We find that even though sensor contributions to PSF chromaticity are subdominant to atmospheric contributions, they can still significantly bias cosmic shear results if left uncorrected, particularly in the redder filter bands and for objects that are off-axis in the field of view.
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Modeling the impact of filter-substrate refraction in the Roman point spread function
Filter-substrate refraction causes dominant lateral shifts yielding 0.3-0.4% PSF size and ellipticity residuals across most Roman bands that exceed weak lensing requirements by an order of magnitude, while longitudinal defocus shifts remain negligible.