High-Contrast Imaging Performance of a Tunable Filter for Space-Based Applications. II. Detection and Characterization Capabilities

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ABSTRACTThe scanning capability of a tunable filter represents an attractive option for performing high-contrast observations through spectral differential imaging (SDI), a speckle-attenuation technique widely used by current ground-based, high-contrast imaging instruments. The performance of such a tunable filter is illustrated through the Tunable Filter Imager (TFI), which used to be part of the science instrument complement of the James Webb Space Telescope (JWST). TFI features a low-order Fabry-Perot etalon enabling imaging spectroscopy at an average resolution of 100 in the 1.5 to 5 μm range. TFI also includes a high-contrast imaging mode featuring a Lyot coronagraph aided by SDI. TFI’s on-sky performance is determined by performing an end-to-end Fresnel propagation of the telescope and instrument using the measured wavefront error maps of TFI’s optical elements and the theoretical wavefront error maps of the optical telescope assembly. Using this simulation, we determine that SDI offers an improvement in contrast ranging from a factor of ∼7 to ∼100, depending on the instrument’s configuration. We present the companion detection capability using both the coronagraphic and noncoronagraphic modes of TFI and demonstrate the characterization capability using the HR 8799 and Fomalhaut systems. The performance of roll subtraction is also determined and compared with that of SDI. We also present the SDI capability of the Near-Infrared Imager and Slitless Spectrograph, the science instrument module to replace TFI in the JWST Fine Guidance Sensor.