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Wavelength-dependent PSFs and their impact on weak lensing measurements

Author(s): Carlsten, SG; Strauss, Michael A; Lupton, Robert H; Meyers, Joshua E; Miyazaki, Satoshi

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Abstract: We measure and model the wavelength dependence of the point spread function (PSF) in the Hyper Suprime-Cam Subaru Strategic Program survey. We find that PSF chromaticity is present in the redder stars that appear smaller than bluer stars in the g, r, and i bands at the 1–2 per cent level and in the z and y bands at the 0.1–0.2 per cent level. From the color dependence of the PSF, we fit a model between the monochromatic PSF size based on weighted second moments, R, and wavelength of the form R(λ) ∝λ−b. We 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 − 100 m, indicating that the atmosphere is dominating the chromaticity. In the best seeing data, we find that the optical system and detector also contribute some wavelength dependence. Meyers & Burchat showed that b must be measured to an accuracy of ∼0.02 not to dominate the systematic error budget of the Large Synoptic Survey Telescope (LSST) weak lensing (WL) survey. Using simple image simulations, we find that b can be inferred with this accuracy in the r and i-bands for all positions in the LSST focal plane, assuming a stellar density of 1 star arcmin−2 and that the optical component of the 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.
Publication Date: 21-Jun-2018
Electronic Publication Date: Sep-2018
Citation: Carlsten, SG, Strauss, Michael A, Lupton, Robert H, Meyers, Joshua E, Miyazaki, Satoshi. (2018). Wavelength-dependent PSFs and their impact on weak lensing measurements. \mnras, 479 (1491 - 1504. doi:10.1093/mnras/sty1636
DOI: doi:10.1093/mnras/sty1636
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Pages: 1491 - 1504
Type of Material: Journal Article
Journal/Proceeding Title: Monthly Notices of the Royal Astronomical Society
Version: Final published version. Article is made available in OAR by the publisher's permission or policy.

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