1804.04277
Wavelength dependent PSFs and their impact on weak lensing measurements
Carlsten, Strauss, Lupton, Meyers, Miyazaki
Measure and model the wavelength dependence of the PSF in the HSC SSP survey. Find that PSF chromaticity is present in that redder stars appear smaller than bluer stars in the g, r, and i-bands at the 1-2% level and in the z and y-bands at the 0.1-0.2% level. From the color dependence of the PSF, fit a model between the monochromatic PSF trace radius, R, and wavelength of the form R(lambda)~lambda^b. Find values of b between -0.2 and -0.5, depending on the epoch and filter. This is consistent with the expectations of a turbulent atmosphere with an outer scale length of ~10-100m, indicating that the atmosphere is dominating the chromaticity. Find evidence in the best seeing data that the optical system and detector also contribute some wavelength dependence. Meyers and Burchat (2015) showed that b must be measured to an accuracy of ~0.02 not to dominate the systematic error budget of the LSST WL survey. Using simple image of simulations, find that b can be inferred with this accuracy in the r and i-bands for all positions in the LSST field of view, assuming a stellar density of 1 star acrmin^-2 and that the optical PSF can be accurately modeled. Therefore, it is possible to correct for most, if not all, of the bias that the wavelength-dependent PSF will introduce into an LSST-like WL survey.
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