CUBES: cassegrain U-band Brazil-ESO spectrograph

Abstract

CUBES is a high-efficiency, medium-resolution (R∼20,000) ground based UV (300–400 nm) spectrograph, to be installed in the cassegrain focus of one of ESO’s VLT unit telescopes in 2017/18. The CUBES project is a joint venture between ESO and IAG/USP, and LNA/MCTI. CUBES will provide access to a wealth of new and relevant information for stellar as well as extragalactic sources. Main science cases include the study of beryllium and heavy elements in metal-poor stars, the direct determination of carbon, nitrogen and oxygen abundances by study of molecular bands in the UV range, as well as the study of active galactic nuclei and the quasar absorption lines. With a streamlined modern instrument design, high efficiency dispersing elements and UV-sensitive detectors, it will give a significant gain in sensitivity over existing ground based medium-high resolution spectrographs, enabling vastly increased sample sizes accessible to the astronomical community. We present here a brief overview of the project including the status, science cases and a discussion of the design options

Fingerprint of the first stars: multi-enriched extremely metal-poor stars in the TOPoS survey

“…Future spectrographs in the UV to detect these elements are e.g. CUBES (Barbuy et al 2014), the Ultraviolet Multi-Object Spectrograph (LUMOS, France et al 2017) on board the future LUVOIR space telescope, or the UV spectrographs on HabEx or CETUS, two further mission in their concept planning phase (Mennesson et al 2016;Heap & CETUS Team 2017).…”

Revisiting the science case for near-UV spectroscopy with the VLT

“…As noted in the introduction, we anticipate demand from the community to address more topics than those described here. For instance, observations of planetary nebulae, close binaries, symbiotic stars, and several AGN cases were discussed by Barbuy et al (2014), and the detailed Phase A case included a significant section on interstellar studies in the local Universe. Moreover, we expect significant interest in the context of transient follow-up, particularly given new facilities such as MeerLICHT and BlackGEM (see Groot et al papers from SPIE conf.…”

“…We are now planning the technical work to advance the instrument concept beyond that presented by Barbuy et al (2014). The dispersion grating is a vital ingredient in delivering the high efficiency desireda prototype fused-Si transmission grating has been manufactured by Fraunhofer IOF and will be characterised in the coming year.…”

“…The CUBES study investigated a spectrograph operating at 'ground UV' wavelengths (spanning 300-400 nm) to open-up exciting new scientific opportunities compared to the (then) planned instrumentation suite for Paranal Observatory. Overviews of the CUBES science case and Phase A concept for a high-throughput, medium resolution (R~20,000) spectrograph were presented by Barbuy et al (2014) and Bristow et al (2014).…”

Reactive ion beam etching of highly dispersive, high-efficiency transmission gratings for the VIS range

“…Highly dispersive surface transmission gratings are also attractive for further applications, e.g., spectral beam combining 15 for laser diode stacks, polarization beam splitters, 16 and spectroscopy. 17 In the highly dispersive regime with period-to-wavelengthratios <0.7, Fresnel-like reflection losses due to imperfect effective refractive index matching severely impair obtainable diffraction efficiencies for surface transmission gratings as well as tolerance windows regarding the grating profile shape. To overcome these issues, different methods have been proposed, e.g., multilayer structures, embedded gratings and tapered profiles.…”