JWST/NIRISS has a non-redundant aperture mask (NRM) for use with its F380M, F430M, F480M and F277W filters. In addition to high-resolution imaging with moderate contrast, the NRM provides better astrometric accuracy over a wide field of view than regular imaging. We investigate the accuracy achievable with the NRM by using an image-plane algorithm to analyze the PSFs of a point source that were obtained at a fixed pixel location with sub-pixel dithers during the second Cryo-Vacuum test campaign of the Integrated Science Instrument Module at NASA’s Goddard Space Flight Center. Astrometry of brown dwarfs with the NRM will be sensitive to the presence of terrestrial planets and can be used to probe the architecture of planetary systems around these objects.
We present several engineering and algorithmic aspects of non-redundant masking (NRM) as they pertain to the James Webb Space Telescope (JWST). NRM's fundamental data structures have multiple uses in wavefront sensing as well in as high resolution imaging. Kernel phases are a full aperture generalization of NRM applicable to moderate and high Strehl ratio images. Eigenphases, the complement to kernel phases, provide wavefront sensing with single in-focus images. Thus this set of phases is relevant to wavefront sensing with routine science images on any Nyquist-sampled science camera on JWST. We attempt to organize these apparently diverse aspects of such Fizeau interferometry into an inter-related picture in order to facilitate their development and potential use on JWST and future space telescopes.