The JWST Early Release Science Program for Direct Observations of Exoplanetary Systems IV: NIRISS Aperture Masking Interferometry Performance and Lessons Learned

Kavli Affiliate: Bruce Macintosh

| First 5 Authors: Steph Sallum, Shrishmoy Ray, Jens Kammerer, Anand Sivaramakrishnan, Rachel Cooper

| Summary:

We present a performance analysis for the aperture masking interferometry
(AMI) mode on board the James Webb Space Telescope Near Infrared Imager and
Slitless Spectrograph (JWST/NIRISS). Thanks to self-calibrating observables,
AMI accesses inner working angles down to and even within the classical
diffraction limit. The scientific potential of this mode has recently been
demonstrated by the Early Release Science (ERS) 1386 program with a deep search
for close-in companions in the HIP 65426 exoplanetary system. As part of ERS
1386, we use the same data set to explore the random, static, and calibration
errors of NIRISS AMI observables. We compare the observed noise properties and
achievable contrast to theoretical predictions. We explore possible sources of
calibration errors and show that differences in charge migration between the
observations of HIP 65426 and point-spread function calibration stars can
account for the achieved contrast curves. Lastly, we use self-calibration tests
to demonstrate that with adequate calibration NIRISS F380M AMI can reach
contrast levels of $sim9-10$ mag at $gtrsim lambda/D$. These tests lead us
to observation planning recommendations and strongly motivate future studies
aimed at producing sophisticated calibration strategies taking these systematic
effects into account. This will unlock the unprecedented capabilities of
JWST/NIRISS AMI, with sensitivity to significantly colder, lower-mass
exoplanets than lower-contrast ground-based AMI setups, at orbital separations
inaccessible to JWST coronagraphy.

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