Polarized point spread functions of an instrument

Context . Studies of image formation in astronomical instruments are often conducted under the assumption that light polarization has no significant effect. When diffraction effects are considered, they are typically treated using scalar point spread functions. Aims . We address the general problem by highlighting the potential effect of polarization and assessing it for a specific instrument by estimating point spread functions for all four Stokes parameters. Methods . Using dedicated partial occulters and pinholes installed as calibration tools for the TuMag instrument on board the S UNRISE III mission, we derived polarized point response functions by exploiting two mathematical properties. Results . A new description of the response of an optical instrument under polarized illumination and a description of its determination in the laboratory are proposed. An application to the TuMag instrument is presented.