PSFuv

PSFuv stands for the ultraviolet point spread function, a characterization of how an optical system forms images of point sources in the ultraviolet portion of the spectrum. It describes the two-dimensional distribution of light in the image plane produced by a single, unresolved source as observed by UV instruments. PSFuv depends on wavelength, aperture geometry, optical aberrations, diffraction, and detector sampling, and is usually specified for a given optical configuration or field position.

In theory, the PSF is the squared magnitude of the Fourier transform of the pupil function. For an ideal circular aperture, the diffraction-limited PSF is an Airy disk with a radiative pattern set by the ratio of wavelength to aperture diameter. Real UV systems incorporate aberrations and scattering, which broaden the core and produce extended wings. The PSF is linked to the optical transfer function (OTF) and modulation transfer function (MTF), tools used to characterize a system's resolution across spatial frequencies.

Measurement and modeling: PSFuv is estimated from observations of bright, isolated stars, or generated by optical models that include telescope geometry, coatings, and detector effects. In UV astronomy, space-based platforms are typical because Earth's atmosphere absorbs most UV light; ground-based UV work is limited and typically relies on high-altitude facilities or correction techniques. PSFuv accuracy is essential for accurate photometry, astrometry, image deconvolution, and crowded-field analyses.

See also: Point spread function, Ultraviolet astronomy, Diffraction, TinyTim (HST PSF modeling).