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Arxiv: The JWST Early Release Science Program for Direct Observations of Exoplanetary Systems III: Aperture Masking Interferometric Observations of the star HIP 65426 Published: 10/17/2023 9:09:40 PM Updated: 10/14/2024 6:47:06 PM

Paper abstract: We present aperture masking interferometry (AMI) observations of the star HIP65426 at 3.8\,\rm{\mu m} as a part of the JWST Direct Imaging Early ReleaseScience (ERS) program obtained using the Near Infrared Imager and SlitlessSpectrograph (NIRISS) instrument. This mode provides access to very small innerworking angles (even separations slightly below the Michelson limit of0.5\lambda/D for an interferometer), which are inaccessible with theclassical inner working angles of the JWST coronagraphs. When combined withJWST's unprecedented infrared sensitivity, this mode has the potential to probea new portion of parameter space across a wide array of astronomicalobservations. Using this mode, we are able to achieve a 5\sigma contrast of\Delta m{~}7.62{\pm}0.13 mag relative to the host star at separations{\gtrsim}0.07{"}, and the contrast deteriorates steeply at separations{<~}0.07{"}. However, we detect no additional companions interior tothe known companion HIP 65426 b (at separation {~}0.82{"} or,87^{+108}_{-31}\,\rm{au}). Our observations thus rule out companions moremassive than 10{-}12\,\rm{M_{Jup}} at separations {~}10{-}20\,\rm{au}from HIP 65426, a region out of reach of ground or space-based coronagraphicimaging. These observations confirm that the AMI mode on JWST is sensitive toplanetary mass companions at close-in separations ({\gtrsim}0.07{"}), evenfor thousands of more distant stars at ~100 pc, in addition to the starsin the nearby young moving groups as stated in previous works. This result willallow the planning and successful execution of future observations to probe theinner regions of nearby stellar systems, opening an essentially unexploredparameter space.