Proceedings Article | 29 August 2022
Karen Disseau, Didier Boudon, Diane Chapuis, Eric Daguisé, Aurélien Jarno, Alexandre Jeanneau, Jens-Kristian Krogager, Florence Laurent, Matthew Lehnert, Jean-Emmanuel Migniau, Arlette Pécontal, Emmanuel Pécontal, Alban Remillieux, Johan Richard
KEYWORDS: Sensors, Optical fibers, Spectrographs, Lamps, Spectral resolution, Manufacturing, Light sources, Cameras
4MOST, the 4m Multi Object Spectroscopic Telescope, is an upcoming optical, fiber-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 the leadership of the Leibniz-Institut für Astrophysik Potsdam (AIP). 4MOST is currently in its Assembly, Integration and Tests Phase with an expected start of science operations in 2023. The design of 4MOST features 2436 fibers split into two low-resolution spectrographs (1624 fibers, 370-950 nm, R < 4000) and a high-resolution spectrograph (812 fibers, ~44-69 nm coverage, R < 18000). A fiber positioner covers a hexagonal field of view of ~4.1 deg². CRAL has the full responsibility of the Low Resolution Spectrographs. Each of them is composed of an off-axis collimator collecting the f/3 beam coming from the fibers and providing a 200 mm collimated beam, which is then split into three arms thanks to two dichroics. Each arm is composed of a Schmidt corrector, a VPHG, an f/1.73 camera and a standard 6k by 6k 15µm pixel detector. Manufacturing, Assembly, Integration and Test (MAIT) phase of the LRS started in May 2018. The first LRS has now been fully integrated, aligned and tested and its Local Acceptance Review on site at CRAL passed successfully in December 2021. This paper describes the procedures developed to test the spectrograph and demonstrate its compliance with the requirements. Performances achieved are presented throughout the paper, especially in terms of spectral resolving power and sampling, spectral purity, cross-talk, throughput, straylight, light tightness and stability.
