THE CIRCUMSTELLAR IMAGER - DIRECT-DETECTION OF EXTRA-SOLAR PLANETARY SYSTEMS

The Astrometric Imaging Telescope (AIT) is designed to probe the circu mstellar environment by both direct imaging and indirect astrometric m easurements. The Circumstellar Imager (CI) is a coronagraphic camera a nd is the direct imaging component of the AIT. The CI is designed to o btain high-sensitivity images of the circumstellar region. It provides crucial non-inferential information relating to the frequency, origin , and evolution of planetary systems and all forms of circumstellar ma tter. Such imaging is usually limited by the scattered and diffracted light halos of the star itself, which are greatly suppressed in the CI by mating a novel high-efficiency coronagraph with a phase-compensate d optical system. For faint point sources in the circumstellar region, the CI will have a sensitivity in excess of 5 magnitudes fainter than the as-designed Hubble Space Telescope (HST). Laboratory data are sho wn for the coronagraph, which, in a diffraction-limited environment, i s capable of suppressing the stellar diffraction sidelobes by several orders of magnitude without significant sacrifice of field of view. In order to realize the high rejection levels inherent in the coronagrap h design, it is necessary to limit scatter in the optical systems, imp osing a mid-spatial frequency figure error requirement an order of mag nitude smaller than that of the HST. Experimental data directed toward meeting this requirement are also shown.