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The HST/WFC3 IR Point Spread Function: A 13-Year
Empirical Characterization for Precision Astronomy in
the JWST Era
Tony Eugene Ford
Independent Researcher
Abstract
We present the first systematic empirical characterization of the Hubble Space
Telescope’s Wide Field Camera 3 infrared channel (WFC3/IR) point spread function,
analyzing 512 high-quality PSF measurements from 13 years of archival observations
(2010–2023). Using a statistically robust sample across multiple filters with precise
focus values (–2.0 to +2.0 µm), we quantify: (1) focus-dependent FWHM variations of
18.7% across the operational range, following a parabolic relationship with minimum
at focus =–0.2 µm (FWHM(focus) = 1.92 + 0.031·focus2 pixels, R2 = 0.89); (2)
exceptional photometric stability with RMS variations <2.3% over decade timescales;
(3) astrometric precision of 20.3 ± 8.7 milliarcseconds, enabling detection of 0.5MJup
exoplanets at 10 pc; and (4) empirical detection limits for anomalous PSF
Project Samples
