Proceedings Article | 18 July 2024
Casper Farret Jentink, Francesco Pepe, Christophe Lovis, Sébastien Bovay, François Wildi, Bruno Chazelas, Michaël Sordet, Étienne Artigau, René Doyon, Frédérique Baron, Vincent Bourrier, Romain Allart, François Cochard
KEYWORDS: Calibration, Spectrographs, Telescopes, Equipment, Helium, Cameras, Exoplanets, Vacuum, Planets, Exoplanetary science, Volume Bragg gratings, Diffraction gratings, Echelle gratings, Astronomical spectroscopy
This paper provides a comprehensive overview of the subsystems of the NIGHT instrument. NIGHT (the Near Infrared Gatherer of Helium Transits) is a narrowband, high-resolution spectrograph, marking the first dedicated survey instrument for exoplanetary atmosphere observations. Developed through a collaboration between the Observatory of Geneva, several other Swiss institutes, and the Université de Montréal, NIGHT aims to conduct an extensive statistical survey of helium atmospheres around 100+ exoplanets over several years. The instrument will report new detections of helium in exoplanet atmospheres and perform temporal monitoring of a subset of these. NIGHT measures absorption from the metastable helium state during exoplanet transits, observable in a triplet of lines around 1083.3 nm. The instrument comprises a vacuum enclosure housing the spectrograph, a front end unit for fiber injection at the telescope’s focal plane, and a calibration and control rack containing calibration light sources and control hardware. The spectrograph is optimized for efficiency around the helium triplet, achieving a throughput of approximately 71%, uniform across wavelength and polarization. The primary disperser employs a volume-phaseholographic grating in a unique double-pass configuration, enabling a spectral resolution of 75 000 while maintaining high throughput. The detector is a HAWAII-1 1024 × 1024 infrared array, cooled to 85K, with the spectrograph operating at room temperature. A shortpass filter at 85 K, positioned in front of the detector, filters out longer infrared wavelengths. Thanks to its relatively high throughput, NIGHT on a 2-m class telescope is predicted to be as sensitive as existing high-resolution spectrographs on 4-m class telescopes. The front end unit injects starlight and sky background into two separate optical fibers leading to the spectrograph. It also performs near-infrared guiding and includes a mechanism for injecting calibration light into either fiber. The assembly and optical alignment of NIGHT’s spectrograph and front end unit are scheduled for July-September 2024, with the first light anticipated before early 2025. Following commissioning, NIGHT is expected to begin its baseline survey, requiring 75 nights per year.
