MIRC-X and MYSTIC are six-telescope near-infrared beam (1.08-2.38μm) combiners at the CHARA Array on Mt Wilson CA, USA. Ever since the commissioning of MIRC-X (J and H bands) in 2018 and MYSTIC (K bands) in 2021, they have been the most popular and over-subscribed instruments at the array. Observers have been able to image stellar objects with sensitivity down to 8.1mag in H and 7.8mag in K-band under the very best conditions. In 2022 MYSTIC was upgraded with a new ABCD mode using the VLTI/GRAVITY 4-beam integrated optics chip, with the goal of improving the sensitivity and calibration. The ABCD mode has been used to observe more than 20T Tauri stars; however, the data pipeline is still being developed. Alongside software upgrades, we detail planned upgrades to both instruments in this paper. The main upgrades are: 1) Adding a motorized filter wheel to MIRC-X along with new high spectral resolution modes 2) Updating MIRC-X optics to allow for simultaneous 6T J+H observations 3) Removing the warm window between the spectrograph and the warm optics in MYSTIC 4) Adding a 6T ABCD mode to MIRC-X in collaboration with CHARA/SPICA 5) Updating the MIRC-X CRED-ONE camera funded by Prof. Kraus from U. Exeter 6) Carrying out science verification of the MIRC-X polarization mode 7) Developing new software for ABCD-mode data reduction and more efficient calibration routines. We expect these upgrades to not only improve the observing experience, but also increase the sensitivity by 0.4mag in J+H-bands, and 1mag in K-band.
We report progress on Project Prime (PRecision Interferometry with MIRC for Exoplanets) to detect exoplanets using precision closures using MIRC-X and MYSTIC at CHARA. Our investigations include modeling systematics caused by OPD drifts, differential dispersion, beamtrain birefringence, and flatfielding errors. Injection tests suggest we can recover hot Jupiter companions as faint at 1/5000 of the host star brightness with 4 nights of observing and we will present some results of our recent searches for the hot Jupiters. Our upper limits are starting to constrain current-generation Global Circulation Models (GCMs). We propose the addition of modest nulling (10:1) to today’s interferometers in order to vastly increase the ease of this work and to open up many more targets for detections.
BIFROST is the short-wavelength, high-spectral resolution instrument in the Asgard Suite of VLTI visitor instruments. It will be optimized for spectral line studies in the Y, J, and H bands (1.05-1.75 μm) that include many strong lines & molecular features. In this presentation, we outline the BIFROST science drivers that have guided our design choices and map them against the operational modes that are being implemented. We give an overview about the status of the project and the milestones from the ongoing integration & testing phase in Exeter to shipping & commissioning on Paranal, scheduled for 2025 and 2026. We review the BIFROST subsystems and discuss how they interface with the broader Asgard Suite. Finally, we outline other BIFROST-related activities pursued by our group that are intended for implementation in BIFROST as part of future upgrades.
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 four-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. 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.
We present science cases and instrument design considerations for the BIFROST instrument that will open the short-wavelength (Y/J/H-band), high spectral dispersion (up to R=25,000) window for the VLT Interferometer. BIFROST will be part of the Asgard Suite of instruments and unlock powerful venues for studying accretion & mass-loss processes at the early/late stages of stellar evolution, for detecting accreting protoplanets around young stars, and for probing the spin-orbit alignment in directly-imaged planetary systems and multiple star systems. Our survey on GAIA binaries aims to provide masses and precision ages for a thousand stars, providing a legacy data set for improving stellar evolutionary models as well as for Galactic Archaeology. BIFROST will enable off-axis spectroscopy of exoplanets in the 0.025-1" separation range, enabling high-SNR, high spectral resolution follow-up of exoplanets detected with ELT and JWST. We give an update on the status of the project, outline our key technology choices, and discuss synergies with other instruments in the proposed Asgard Suite of instruments.
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