Validation of PSF Models for HST and Other Space-Based Observations

Bryan R. Gillis, Tim Schrabback, Ole Marggraf, Rachel Mandelbaum, Richard Massey, Jason Rhodes, Andy Taylor

Research output: Contribution to journalArticlepeer-review


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 which characterise 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 approximately 4e-4. We also show that most of this improvement can be retained through using an updated set of Zernike coefficients, which we provide.
Original languageEnglish
Pages (from-to)5017-5038
Number of pages22
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
Early online date24 Jun 2020
Publication statusPublished - 1 Aug 2020


  • astro-ph.IM

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