MIRC-X: A Highly Sensitive Six-telescope Interferometric Imager at the CHARA Array

Abstract

Michigan InfraRed Combiner-eXeter (MIRC-X) is a new highly sensitive six-telescope interferometric imager installed at the CHARA Array that provides an angular resolution equivalent of up to a 330 m diameter baseline telescope in J- and H-band wavelengths ( mas). We upgraded the original Michigan InfraRed Combiner (MIRC) instrument to improve sensitivity and wavelength coverage in two phases. First, a revolutionary sub-electron noise and fast-frame-rate C-RED ONE camera based on an SAPHIRA detector was installed. Second, a new-generation beam combiner was designed and commissioned to (i) maximize sensitivity, (ii) extend the wavelength coverage to J band, and (iii) enable polarization observations. A low-latency and fast-frame-rate control software enables high-efficiency observations and fringe tracking for the forthcoming instruments of the CHARA Array. Since mid-2017, MIRC-X has been offered to the community and has demonstrated best-case H-band sensitivity down to 8.2 correlated magnitude. MIRC-X uses single-mode fibers to coherently combine the light from six telescopes simultaneously with an image-plane combination scheme and delivers a visibility precision better than 1%, and closure phase precision better than 1°. MIRC-X aims at (i) imaging protoplanetary disks, (ii) detecting exoplanets with precise astrometry, and (iii) imaging stellar surfaces and starspots at an unprecedented angular resolution in the near-infrared. In this paper, we present the instrument design, installation, operation, and on-sky results, and demonstrate the imaging capability of MIRC-X on the binary system ι Peg. The purpose of this paper is to provide a solid reference for studies based on MIRC-X data and to inspire future instruments in optical interferometry.

The First Dynamical Mass Determination of a Nitrogen-rich Wolf–Rayet Star Using a Combined Visual and Spectroscopic Orbit

“…Interferometric observations were obtained with the CHARA Array, which has six one-meter telescopes in a Y-shaped array with baselines ranging from 34-330 m (ten Brummelaar et al 2005) and the upgraded MIRC-X combiner (Monnier et al 2004;Kraus et al 2018;Anugu et al 2018Anugu et al , 2020 in 2019 and 2020. The observations were recorded in the PRISM50 mode which provides a spectral resolution of R = 50 in the H-band between 1.4 and 1.7 micrometer.…”

“…We adopted uniform disk diameters in the H-band for the calibrators from the JMMC stellar diameter catalog (Bourges et al 2017). We inspected the visibilities and closure phases of the calibrators to check for binarity, and also examined the results from the automated pipeline (Anugu et al 2020) which calibrates the calibrators against each other and uses CANDID (Gallenne et al 2015) to determine companion detection limits. We did not find any reliable binary detections for the calibrators.…”

“…Due to the proximity in the sky to WR 140, we used some of the same calibrator stars as given in the analysis of Thomas et al (submitted), with the diameter estimates taken from Bourges et al (2017). All calibrators and data sets are tabulated in Table 1 The closure phase calibration is well tested by Anugu et al (2020), so that we are confident that the sign of the closure phases are correct. The reduction pipeline is discussed in detail by Anugu et al (2020), For the WR star, we measured radial velocities of the He II λ5411 emission line through bisecting the line (see Fig.…”

“…All calibrators and data sets are tabulated in Table 1 The closure phase calibration is well tested by Anugu et al (2020), so that we are confident that the sign of the closure phases are correct. The reduction pipeline is discussed in detail by Anugu et al (2020), For the WR star, we measured radial velocities of the He II λ5411 emission line through bisecting the line (see Fig. 1).…”

Review and scientific prospects of high-contrast optical stellar interferometry

“…The three instruments share a common low-order adaptive optics systems to optimise light injection and aim to adopt a shared communication protocol. For the optical design of BIFROST both an all-in-one coaxial beam combination scheme [44][45][46] and an integrated optics design 47 are considered. In order to enable long integration times on the high-spectral resolution arm, we will utilize fringe tracking through the recently-commissioned GRA4MAT mode or the planned second-generation fringe tracker.…”