Design of the new CHARA instrument SILMARIL: pushing for the sensitivity of a 3-beam combiner in the H- and K-bands

Cyprien Lanthermann; Theo ten Brummelaar; Peter Tuthill; Marc-Antoine Martinod; Edgar Ligon; Douglas Gies; Gail Schaefer; Matthew Anderson

doi:10.1117/12.2628268

26 August 2022 Design of the new CHARA instrument SILMARIL: pushing for the sensitivity of a 3-beam combiner in the H- and K-bands

Cyprien Lanthermann, Theo ten Brummelaar, Peter Tuthill, Marc-Antoine Martinod, Edgar Ligon, Douglas Gies, Gail Schaefer, Matthew Anderson

Author Affiliations +

Proceedings Volume 12183, Optical and Infrared Interferometry and Imaging VIII; 121830N (2022) https://doi.org/10.1117/12.2628268
Event: SPIE Astronomical Telescopes + Instrumentation, 2022, Montréal, Québec, Canada

Abstract

Optical interferometry is a powerful technique to achieve high angular resolution. However, its main issue is its lack of sensitivity, compared to other observation techniques. Efforts have been made in the previous decade to improve the sensitivity of optical interferometry, with instruments such as PIONIER and GRAVITY at VLTI, or MIRC-X and MYSTIC at CHARA. While those instruments pushed on sensitivity, their design focus was not the sensitivity but relative astrometric accuracy, imaging capability, or spectral resolution. Our goal is to build an instrument specifically designed to optimize for sensitivity. This meant focusing our design efforts on different parts of the instrument and investigating new technologies and techniques. First, we make use of the low noise C-RED One camera using e-APD technology and provided by First Light Imaging, already used in the improvement of sensitivity in recent new instruments. We forego the use of single-mode fibers but still favor an image plane design that offers more sensitivity than a pupil plane layout. We also use a minimum number of optical elements to maximize the throughput of the design, using a long focal length cylindrical mirror. We chose to limit our design to 3 beams, to have the capability to obtain closure phases, but not dilute the incoming flux in more beam combinations. We also use in our design an edge filter to have the capability to observe Hand K-band at the same time. We use a low spectral resolution, allowing for group delay fringe tracking but maximizing the SNR of the fringes for each spectral channel. All these elements will lead to a typical limiting magnitude between 10 and 11 in both H- and K-bands.

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Cyprien Lanthermann, Theo ten Brummelaar, Peter Tuthill, Marc-Antoine Martinod, Edgar Ligon, Douglas Gies, Gail Schaefer, and Matthew Anderson "Design of the new CHARA instrument SILMARIL: pushing for the sensitivity of a 3-beam combiner in the H- and K-bands", Proc. SPIE 12183, Optical and Infrared Interferometry and Imaging VIII, 121830N (26 August 2022); https://doi.org/10.1117/12.2628268

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