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  1. Mérand, Antoine ; Sallum, Stephanie ; Sanchez-Bermudez, Joel (Ed.)
    The Michigan Young STar Imager at CHARA (MYSTIC) is a K-band interferometric beam combining instrument funded by the United States 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 meters, 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 utilizes a high frame rate, ultra-low read noise SAPHIRA detector, and implements two beam combiners: a 6-telescope image plane beam combiner, based on the MIRC-X design, for targets as faint as 7.7 Kmag, as well as a 4-telescope 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. Herein, we present the instrument design, review its operational performance, present early commissioning science observations, andmore »propose upgrades to the instrument that could improve its K-band sensitivity to 10th magnitude in the near future.« less
  2. Mérand, Antoine ; Sallum, Stephanie ; Sanchez-Bermudez, Joel (Ed.)
    The Center for High Angular Resolution Astronomy (CHARA) Array is a six-element interferometer with baselines ranging from 34 to 331 m. Three new beam combiners are entering operation: MYSTIC is a 6-telescope combiner for K-band; SPICA is a 6-telescope combiner for the visible R-band; and SILMARIL is a 3-telescope combiner for high sensitivity in H and K-bands. A seventh, portable telescope will use fiber optics for beam transport and will increase the baselines to 1 km. Observing time is available through a program funded by NSF. The programs are solicited and peer-reviewed by NSF’s National Optical Infrared Astronomy Research Laboratory. The open community access has significantly expanded the range of astronomical investigations of stars and their environments. Here we summarize the scientific work and the on-going technical advances of the CHARA Array.
  3. Mérand, Antoine ; Sallum, Stephanie ; Sanchez-Bermudez, Joel (Ed.)
  4. Mérand, Antoine ; Sallum, Stephanie ; Tuthill, Peter G. (Ed.)
    We present a new polarimetric mode for the MIRC-X 6-telescope beam combiner at CHARA. Utilizing the extensive u - v coverage afforded by CHARA this mode will be able to resolve and constrain scattered light in environs at milliarcsecond separations of target stars, a largely unexplored parameter space to-date in astronomy. Notably, this upgrade will allow for the investigation of the scattering properties of the inner dust wall at the sublimation radius of Herbig Ae/Be star disks, dust shells surrounding evolved stars, and gas-rich disks around Be stars. Our design adds a series of rotating half-wave plates, achromatic across J- and H-bands, and a polarizing beamsplitter into the MIRC-X beam path. In this work, we also preview on-sky observations, discussing ongoing work calibrating instrumental polarization effects in the CHARA beam path as well as upgrades to the MIRC-X data reduction pipeline.
  5. We present the fabrication and characterization of 3 dB asymmetric directional couplers for the astronomical K-band at wavelengths between 2.0 and 2.4 µm. The couplers were fabricated in commercial Infrasil silica glass using an ultrafast laser operating at 1030 nm. After optimizing the fabrication parameters, the insertion losses of straight single-mode waveguides were measured to be∼<#comment/>1.2±<#comment/>0.5dBacross the full K-band. We investigate the development of asymmetric 3 dB directional couplers by varying the coupler interaction lengths and by varying the width of one of the waveguide cores to detune the propagation constants of the coupled modes. In this manner, we demonstrate that ultrafast laser inscription is capable of fabricating asymmetric 3 dB directional couplers for future applications in K-band stellar interferometry. Finally, we demonstrate that our couplers exhibit an interferometric fringe contrast of><#comment/>90%<#comment/>. This technology paves the path for the development of a two-telescope K-band integrated optic beam combiner for interferometry to replace the existing beam combiner (MONA) in Jouvence of the Fiber Linked Unit for Recombination (JouFLU) at the Center for High Angular Resolution Astronomy (CHARA) telescope array.