Improvement of coronagraphy using optimal apodizations

摘要

This communication deals with apodization and coronagraphy. For apodization alone, we present analytical studies of point spread functions obtained with a rectangular or a circular telescope apodized by cross-linear or circular prolate spheroidal functions, respectively. Results are compared with sonine apodizations investigated by Nisenson and Papaliolios (2001) for the Apodized Square Aperture project. For coronagraphy, prolate functions are the optimal apodizers for rectangular and circular apertures. With the Roddier & Roddier phase mask technique, these apodizations can produce a total extinction of the star light. For Lyot coronagraphy, the extinction, not complete, is surprisingly good for a reasonable mask size. A comparison between coronagraphy and apodization alone for different telescope aperture shape is in favor to the use of a coronagraph with a circular aperture.