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Validation of PSF models for HST and other space-based observations

Gillis, Bryan R. and Schrabback, Tim and Marggraf, Ole and Mandelbaum, Rachel and Massey, Richard and Rhodes, Jason and Taylor, Andy (2020) Validation of PSF models for HST and other space-based observations. Monthly Notices of the Royal Astronomical Society, 496 (4). pp. 5017-5038. ISSN 0035-8711.

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Forthcoming space-based observations will require high-quality point spread function (PSF) models for weak gravitational lensing measurements. One approach to generating these models is using a wavefront model based on the known telescope optics. We present an empirical framework for validating such models to confirm that they match the actual PSF to within requirements by comparing the models to the observed light distributions of isolated stars. We apply this framework to TINY TIM, the standard tool for generating model PSFs for the Hubble Space Telescope (HST), testing its models against images taken by HST’s Advanced Camera for Surveys in the Wide Field Channel. We show that TINY TIM’s models, in the default configuration, differ significantly from the observed PSFs, most notably in their sizes. We find that the quality of TINY TIM PSFs can be improved through fitting the full set of Zernike polynomial coefficients that characterize the optics, to the point where the practical significance of the difference between model and observed PSFs is negligible for most use cases, resulting in additive and multiplicative biases both of order ∼4 × 10⁻⁴. We also show that most of this improvement can be retained through using an updated set of Zernike coefficients, which we provide.

Item Type:Article
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URLURL TypeDescription Paper
Gillis, Bryan R.0000-0002-4478-1270
Schrabback, Tim0000-0002-6987-7834
Marggraf, Ole0000-0001-7242-3852
Mandelbaum, Rachel0000-0003-2271-1527
Massey, Richard0000-0002-6085-3780
Rhodes, Jason0000-0002-4485-8549
Additional Information:© 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model ( Accepted 2020 June 15. Received 2020 June 8; in original form 2019 November 11. The authors acknowledge useful input on the paper from Lance Miller. The authors acknowledge useful conversations with John Krist about the TINY TIM tool, Matt Lallo about the secondary mirror of HST and the TINY TIM PSF models, and Sami Niemi about the HST focus model. The authors thank the anonymous referee for their input on the paper, including their recommendation to address the issue of jitter and some valuable insight on the issue of the observed bias toward too-large fitted focus offset values. This work is based on observations made with the NASA/ESA Hubble Space Telescope obtained from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5–26555, using imaging data from the GO programmes 11397, 11586, 11653, 11677, 11688, 11724, 11880, 11887, 12166, 12193, 12385, 12389, 12730, and 12734. BRG and ANT thank the UK Space Agency for funding. TS and RMas acknowledge support through ERC H2020-COMPET-2017, project no. 776247. OM acknowledges support from the German Federal Ministry for Economic Affairs and Energy (BMWi) provided via DLR under project nos. 50QE1103 and 50QE2002. RMan was supported by NASA ROSES grant no. 12-EUCLID12-0004. RMas is supported by UK Space Agency grant nos. ST/N001494/1 and ST/V001582/1 and a Royal Society University Research Fellowship. JR was supported by JPL, which is run under a contract for NASA by Caltech and by NASA ROSES grant no. 12-EUCLID12-0004. ANT thanks the Royal Society for a Wolfson Research Merit Award. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement no. 776247. DATA AVAILABILITY. The data underlying this article were accessed from the Barbara A. Mikulski Archive for Space Telescopes (, and may be obtained from the MAST archive at The derived data generated in this research will be shared on reasonable request to the corresponding author.
Funding AgencyGrant Number
NASANAS 5-26555
United Kingdom Space Agency (UKSA)UNSPECIFIED
European Research Council (ERC)776247
Bundesministerium für Wirtschaft und Technologie (BMWi)UNSPECIFIED
Deutsches Zentrum für Luft- und Raumfahrt (DLR)50QE1103
Deutsches Zentrum für Luft- und Raumfahrt (DLR)50QE2002
Science and Technology Facilities Council (STFC)ST/N001494/1
Science and Technology Facilities Council (STFC)ST/V001582/1
Wolfson FoundationUNSPECIFIED
Subject Keywords:gravitational lensing: weak, methods: data analysis
Issue or Number:4
Record Number:CaltechAUTHORS:20201022-161609161
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Official Citation:Bryan R Gillis, Tim Schrabback, Ole Marggraf, Rachel Mandelbaum, Richard Massey, Jason Rhodes, Andy Taylor, Validation of PSF models for HST and other space-based observations, Monthly Notices of the Royal Astronomical Society, Volume 496, Issue 4, August 2020, Pages 5017–5038,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:106241
Deposited By: George Porter
Deposited On:23 Oct 2020 14:17
Last Modified:23 Oct 2020 14:17

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