MYSTIC: a high angular resolution K-band imager at CHARA

Abstract

The Michigan Young Star Imager at CHARA (MYSTIC) is a K-band interferometric beam combining instrument funded by the U.S. National Science Foundation, designed primarily for imaging sub-au scale disk structures around nearby young stars and to probe the planet formation process. Installed at the CHARA Array in July 2021, with baselines up to 331 m, MYSTIC provides a maximum angular resolution of λ∕2B ∼ 0.7 mas. The instrument injects phase-corrected light from the array into inexpensive, single-mode, polarization maintaining silica fibers, which are then passed via a vacuum feedthrough into a cryogenic dewar operating at 220 K for imaging. MYSTIC uses a high frame rate, ultra-low read noise SAPHIRA detector and implements two beam combiners: a six-telescope image plane beam combiner, based on the MIRC-X design, for targets as faint as 7.7 Kmag, as well as a fourtelescope integrated optic beam-combiner mode using a spare chip leftover from the GRAVITY instrument. MYSTIC is co-phased with the MIRC-X (J + H band) instrument for simultaneous fringe-tracking and imaging and shares its software suite with the latter to allow a single observer to operate both instruments. We present the instrument design, review its operational performance, present early commissioning science observations, and propose upgrades to the instrument that could improve its K-band sensitivity to 10th magnitude in the near future.

The CHARA Array Interferometric Program on the Multiplicity of Classical Be Stars: New Detections and Orbits of Stripped Subdwarf Companions

“…The H-band six-beam combiner MIRC-X (upgraded from MIRC and commissioned in 2018 September; Anugu et al 2020b) and the K-band six-beam combiner MYSTIC (installed in 2021 July; Setterholm et al 2023) operate simultaneously, enabling dense (u, v) coverage consisting of 15 independent baselines and 10 independent closed triangles in each band. The main observables are squared visibilities (VIS2) for each baseline and closure phase (CP) for each baseline triangle; while VIS2 is sensitive to the angular extent of the observed target, and decreases with increasing projected baseline if the target is spatially resolved, the CP reveals deviations from point symmetry in the resolved target (for an introduction to optical interferometry and its observables, we refer the reader to Monnier 2003).…”

Vortex Fiber Nulling for Exoplanet Observations: First Direct Detection of M Dwarf Companions around HIP 21543, HIP 94666, and HIP 50319

“…The three companions covered here were previously known only from RV and/or astrometric observations, such that our results represent their first direct detections and provide the first spectra for the companions. Though KPIC VFN alone can provide a detection, in this Letter we complement the VFN observations with CHARA observations using the MIRC-X and MYSTIC beam combiners (Anugu et al 2020;Setterholm et al 2023), which have a demonstrated history of success at these angular separations (e.g., Roettenbacher et al 2015aRoettenbacher et al , 2015bThomas et al 2021;De Furio et al 2022;Lanthermann et al 2023). This allows us to validate the VFN performance in this first demonstration against CHARA's well-established performance.…”

“…The Michigan InfraRed Combiner-eXeter (MIRC-X; Anugu et al 2020) and the Michigan Young STar Imager (MYSTIC; Setterholm et al 2023) on the Georgia State University Center for High Angular Resolution Astronomy (CHARA) Array (ten Brummelaar et al 2005) were used to search for binary companions to all three targets. HIP 94666 and HIP 50319 were observed in 2023 specifically for a brief VFN follow-up program, with the latter target being observed over two nights.…”

Astronomy from the moon in the next decades: from exoplanets to cosmology in visible light and beyond

“…For this purpose, we propose to use a set of optical fibres of different lengths, selected by a mechanical or opto-electronic beam-switching device. The principle would be the same as the two-stage system that has been operating successfully at the CHARA array for more than 20 years [28,29]. A set of fixed length incremental delay lines would be associated with each telescope of the lunar interferometer array.…”