CUBES, the Cassegrain u-band efficient spectrograph: instrument overview after final design review.

Résumé fourni par la source

In the era of Extremely Large Telescopes, the current generation of 8-10m facilities is 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 instrumental efficiency (> 37%) for observations in the near UV (300-405 nm) 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 spectral resolution element at 313 nm for U ∼ 17.5 mag objects in 1h of observations), it will offer new possibilities in many fields of astrophysics: access to key lines of stellar spectra (e.g. lighter elements, in particular Beryllium), extragalactic studies (e.g. the circumgalactic medium of distant galaxies, cosmic UV background) and follow-up of explosive transients. We present the CUBES instrument design, which successfully passed its Final Design Review in July 2025 and is now at the beginning of the MAIT phase, summarizing the relevant technical requirements, the hardware architecture and the overall project schedule. We give an overview of the optical, mechanical, electrical design of the different subsystems (from the telescope adapter and support structure, through the main opto-mechanical path, including calibration unit, detector devices and cryostat control, main control electronics), that are described in more detail in dedicated papers at this conference. A novel feature is the Active Flexure Compensation (AFC), essential to achieve high RV accuracy and resolution for long exposures, while gravity and temperature conditions change due to the instrument location at the Cassegrain focus. Installation at the VLT is planned for 2030 and first science operations in 2031.

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