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Arxiv: The JWST Early Release Science Program for Direct Observations of Exoplanetary Systems IV: NIRISS Aperture Masking Interferometry Performance and Lessons Learned Published: 10/17/2023 9:00:07 PM Updated: 3/11/2024 10:19:56 PM

Paper abstract: We present a performance analysis for the aperture masking interferometry(AMI) mode on board the James Webb Space Telescope Near Infrared Imager andSlitless Spectrograph (JWST/NIRISS). Thanks to self-calibrating observables,AMI accesses inner working angles down to and even within the classicaldiffraction limit. The scientific potential of this mode has recently beendemonstrated by the Early Release Science (ERS) 1386 program with a deep searchfor close-in companions in the HIP 65426 exoplanetary system. As part of ERS1386, we use the same data set to explore the random, static, and calibrationerrors of NIRISS AMI observables. We compare the observed noise properties andachievable contrast to theoretical predictions. We explore possible sources ofcalibration errors and show that differences in charge migration between theobservations of HIP 65426 and point-spread function calibration stars canaccount for the achieved contrast curves. Lastly, we use self-calibration teststo demonstrate that with adequate calibration NIRISS F380M AMI can reachcontrast levels of ~9-10 mag at \gtrsim \lambda/D. These tests lead usto observation planning recommendations and strongly motivate future studiesaimed at producing sophisticated calibration strategies taking these systematiceffects into account. This will unlock the unprecedented capabilities ofJWST/NIRISS AMI, with sensitivity to significantly colder, lower-massexoplanets than lower-contrast ground-based AMI setups, at orbital separationsinaccessible to JWST coronagraphy.