CRIRES$^{+}$ on sky at the ESO Very Large Telescope

TL;DR

The CRIRES$^{+}$ upgrade on the VLT significantly enhances infrared spectroscopic capabilities by expanding wavelength coverage, improving detectors, and adding new features, enabling advanced astronomical observations.

Contribution

This paper details the design, implementation, and on-sky performance of the CRIRES$^{+}$ upgrade, a major enhancement to the original instrument.

Findings

Expanded wavelength coverage by up to ten times

Successful installation and commissioning at the VLT

Demonstrated improved on-sky performance and capabilities

Abstract

The CRyogenic InfraRed Echelle Spectrograph (CRIRES) Upgrade project CRIRES$^{+}$ extended the capabilities of CRIRES. It transformed this VLT instrument into a cross-dispersed spectrograph to increase the wavelength range that is covered simultaneously by up to a factor of ten. In addition, a new detector focal plane array of three Hawaii 2RG detectors with a 5.3 $\mu$m cutoff wavelength replaced the existing detectors. Amongst many other improvements, a new spectropolarimetric unit was added and the calibration system has been enhanced. The instrument was installed at the VLT on Unit Telescope 3 at the beginning of 2020 and successfully commissioned and verified for science operations during 2021, partly remotely from Europe due to the COVID-19 pandemic. The instrument was subsequently offered to the community from October 2021 onwards. This article describes the performance and capabilities of the upgraded instrument and presents on sky results.