CUBES, the Cassegrain U-Band Efficient Spectrograph

TL;DR

CUBES is a high-efficiency UV spectrograph designed for 8-10m telescopes, enabling detailed astrophysical studies in the near UV range with high spectral resolution and throughput.

Contribution

This paper presents the design and development of CUBES, a novel spectrograph optimized for near UV observations on large telescopes, with significant improvements in efficiency and spectral resolution.

Findings

Design achieves >40% efficiency in 305-400 nm range.

Spectral resolving power of R>20,000 for high-resolution mode.

Expected to enable new astrophysical research in stellar and extragalactic UV spectra.

Abstract

In the era of Extremely Large Telescopes, the current generation of 8-10m facilities are likely to remain competitive at ground-UV wavelengths for the foreseeable future. The Cassegrain U-Band Efficient Spectrograph (CUBES) has been designed to provide high-efficiency (>40%) observations in the near UV (305-400 nm requirement, 300-420 nm goal) at a spectral resolving power of R>20,000 (with a lower-resolution, sky-limited mode of R ~ 7,000). With the design focusing on maximizing the instrument throughput (ensuring a Signal to Noise Ratio (SNR) ~20 per high-resolution element at 313 nm for U ~18.5 mag objects in 1h of observations), it will offer new possibilities in many fields of astrophysics, providing access to key lines of stellar spectra: a tremendous diversity of iron-peak and heavy elements, lighter elements (in particular Beryllium) and light-element molecules (CO, CN, OH), as well as Balmer lines and the Balmer jump (particularly important for young stellar objects). The UV range is also critical in extragalactic studies: the circumgalactic medium of distant galaxies, the contribution of different types of sources to the cosmic UV background, the measurement of H2 and primordial Deuterium in a regime of relatively transparent intergalactic medium, and follow-up of explosive transients. The CUBES project completed a Phase A conceptual design in June 2021 and has now entered the detailed design and construction phase. First science operations are planned for 2028.