The instrumentation plan for the ELT foresees the ArmazoNes high Dispersion Echelle Spectrograph (ANDES). The ANDES-project and consortium entered phase B in January 2022 and underwent several (internal and external) revisions by now to ensure that the requirements and eventually the challenging goals can be met by the physical design of the spectrograph.
Among its main scientific goals are the detection of atmospheres of exoplanets and the determination of fundamental physical constants. For this, high radial velocity precision and accuracy are required. Even though the ANDES-spectrograph is designed for maximum intrinsic stability, a calibration and thus a calibration unit is mandatory. To allow for maximum flexibility and modularity the calibration unit is physically split into three calibration units.
We show the design of the calibration units and their individual components, where possible. This includes the electronics, the mechanics, the software supporting and controlling the light guiding and calibration sources.
KEYWORDS: Spectrographs, Waveguides, Second harmonic generation, Fabry Perot interferometers, Calibration, Supercontinuum generation, Sum frequency generation, Frequency combs
Next generation extreme precision radial velocity (EPRV) instruments such as the ANDES spectrograph of the Extremely Large Telescope will require an unprecedentedly high-precision calibration approach, particularly in the UB band region in which the most dense stellar absorption lines are present. For this purpose, astrocombs delivering thousands of atomically referenced, evenly-spaced calibration lines across a broad spectrum have the potential to be ideal calibration sources. Here, we report a novel and effective approach to generating a laser frequency comb with a multi- GHz mode spacing covering a broad wavelength range in the UB band. The approach is based on nonlinear mixing between near-infrared ultrafast laser pulses in a MgO:PPLN waveguide. The generated 1-GHz comb, spanning 390–520 nm, was filtered to a 30 GHz sub-comb using a low-dispersion Fabry-Perot etalon. The resultant UB-band astrocomb was then captured on a lab-built cross-dispersion echelle-prism spectrograph, demonstrating well resolved comb lines across the etalon bandwidth of 392–472 nm.
The first generation of ELT instruments includes an optical-infrared high resolution spectrograph, indicated as ELT-HIRES and recently christened ANDES (ArmazoNes high Dispersion Echelle Spectrograph). ANDES consists of three fibre-fed spectrographs ([U]BV, RIZ, YJH) providing a spectral resolution of ∼100,000 with a minimum simultaneous wavelength coverage of 0.4-1.8 μm with the goal of extending it to 0.35-2.4 μm with the addition of an U arm to the BV spectrograph and a separate K band spectrograph. It operates both in seeing- and diffraction-limited conditions and the fibre-feeding allows several, interchangeable observing modes including a single conjugated adaptive optics module and a small diffraction-limited integral field unit in the NIR. Modularity and fibre-feeding allows ANDES to be placed partly on the ELT Nasmyth platform and partly in the Coudé room. ANDES has a wide range of groundbreaking science cases spanning nearly all areas of research in astrophysics and even fundamental physics. Among the top science cases there are the detection of biosignatures from exoplanet atmospheres, finding the fingerprints of the first generation of stars, tests on the stability of Nature’s fundamental couplings, and the direct detection of the cosmic acceleration. The ANDES project is carried forward by a large international consortium, composed of 35 Institutes from 13 countries, forming a team of almost 300 scientists and engineers which include the majority of the scientific and technical expertise in the field that can be found in ESO member states.
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