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WFC3 Observed PSF Search through MAST

To facilitate users in building WFC3 PSFs appropriate for their observations, we annually update our database of WFC3 observed PSFs. The sources in the database were measured using HST1PASS. As of February 2024, the database contains over 57 million PSFs from external WFC3 observations taken between 2009 and 2022. Specifically, it contains 32 million WFC3/UVIS sources (29 million unsaturated and 3 million saturated), and 25.2 million WFC3/IR sources (25 million unsaturated and 0.2 million saturated). These PSFs can be used to generate custom PSFs appropriate for specific observations (e.g. filter, detector, focus-value, etc.) or to build delta-PSFs, which can be used in conjunction with the library PSFs. These resulting PSFs are expected to be more representative of their observations, and hence may help in accurate photometry/astrometry. All supplemental details are available in ISR 2021-12 (Dauphin et al.)

A similar database is available for WFPC2, containing 25 million sources (15 million unsaturated and 10 million saturated) from external observations during the instrument’s lifetime

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The database of WFC3 observed PSFs are available on the MAST Portal. To access the WFC3 PSF database:

  • Select “WFC3 PSF” under “Select a collection” (a similar option is available for the WFPC2 PSF database).
  • For WFC3, choose either “UVIS” or “IR” under “Waveband”.
  • Click “Advanced Search” to select specific PSF parameters to search the database.
    • Note that there is a pre-selected “Good Quality PSF Subset” (298 PSFs for UVIS, 163 PSFs for IR, 60 PSFs for WFPC2), which may serve as a guide to select the various parameters.
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The search parameters are described here. Note the database utilizes the HST Focus Model for predicting the PSF’s focus in microns

Once satisfied with the advanced searching parameters, click "Search". The PSFs can be visually inspected by clicking the “Show Cutout”, or by clicking "Album View" and "Cutout". The download option allows users to download the raw and the calibrated (flt and flc) files.

Jupyter Notebooks for accessing the databases via Python and building custom PSF models can be found here.

Last Updated: 05/21/2025

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