4MOST Low Resolution Spectrographs Characterization in Chile

Florence Laurent; Didier Boudon; Eric Daguise; Remi Giroud; Aurelien Jarno; Alexandre Jeanneau; Andreas Kelz; Jens-Kristian Krogager; Victor Mauger-Vauglin; Jean-Emmanuel Migniau; Matthew Lehnert; Flora Paganelli; Arlette Pecontal; Emmanuel Pecontal; Alban Remillieux; Johan Richard; Allar Saviauk

arXiv · 2609.01219

4MOST Low Resolution Spectrographs Characterization in Chile

Florence Laurent·Didier Boudon·Eric Daguise·Remi Giroud·Aurelien Jarno·Alexandre Jeanneau·Andreas Kelz·Jens-Kristian Krogager·Victor Mauger-Vauglin·Jean-Emmanuel Migniau·Matthew Lehnert·Flora Paganelli·Arlette Pecontal·Emmanuel Pecontal·Alban Remillieux·Johan Richard·Allar Saviauk

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Abstract

4MOST, the 4m Multi Object Spectroscopic Telescope, is the optical, fibre-fed, MOS facility for the VISTA telescope at ESO's Paranal Observatory in Chile. Its main science drivers are in the fields of galactic archeology, high-energy physics, galaxy evolution and cosmology. The 4MOST consortium consists of several institutes in Europe and Australia under leadership of the Leibniz-Institut fur Astrophysik Potsdam (AIP). This paper focuses on the successful testing, installation and technical commissioning of the Low Resolution Spectrographs (LRS-A and B) for the 4MOST instrument at ESO's Paranal Observatory, Chile. This work was completed on October 18. 2025. Details on the assembly, integration, and performance of both 4MOST spectrographs from their arrival in the integration hall through to the telescope installation are provided. Attention is given to the optimization of procedures implemented to enhance performance and meet the expected top-level requirements. The 4MOST LRS features 2436 fibres split into two low-resolution spectrographs LRS-A and LRS-B (1624 fibres, three arms, 370-950 nm, R > 4000) and one high-resolution spectrograph (812 fibres, three arms, ~44-69 nm coverage each, R > 18000). The fibre positioner covers a hexagonal field of view of ~4.1 deg2. The fibers are 85 {\mu}m core with an output beam at f/3. The Centre de Recherche Astrophysique de Lyon (CRAL) had the full responsibility for the two low-resolution spectrographs. Each of them is composed of an off-axis Schmidt collimator that produces a 200 mm beam, which is split into three spectral arms by dichroics and directed to F/1.73 cameras with standard 6k x 6k 15 microns pixel CCD detectors.

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Florence Laurent, Didier Boudon, Eric Daguise, Remi Giroud, Aurelien Jarno, Alexandre Jeanneau, Andreas Kelz, Jens-Kristian Krogager, Victor Mauger-Vauglin, Jean-Emmanuel Migniau, Matthew Lehnert, Flora Paganelli, Arlette Pecontal, Emmanuel Pecontal, Alban Remillieux, Johan Richard, Allar Saviauk. 2026-09-01. 4MOST Low Resolution Spectrographs Characterization in Chile. https://arxiv.org/abs/2609.01219

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