14 February 2023 Assembly and alignment of the 4-metre multi-object spectroscopic telescope wide field corrector
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Abstract

The 4-metre multi-object spectroscopic telescope (4MOST) is a fiber-fed multi-object spectrograph for the VISTA telescope at the European Southern Observatory (ESO) Paranal Observatory in Chile. The goal of the 4MOST project is to create a general purpose and highly efficient spectroscopic survey facility for astronomers in the 4MOST consortium and the ESO community. The instrument itself will record 2436 simultaneous spectra over a ∼4.2 square deg field of view and consists of an optical wide-field corrector (WFC), a fiber positioner system based on a tilting spine design, and three spectrographs giving both high and low spectral dispersion. The WFC comprises of six lenses grouped into four elements, two of which are cemented doublets that act as an atmospheric dispersion corrector. The first lens element is 0.9 m in diameter while the diameter of the other elements is 0.65 m. For the instrument to meet its science goals, each lens was aligned to be well within ∼100 μm—a major challenge. This was achieved using contact metrology methods supplemented by pencil beam laser probes. In particular, an off-axis laser beam system has been implemented to test the optics’ alignment before and after shipment. This work details the alignment and assembly methods and presents the latest results on the achieved lens positioning and projected performance of the WFC.

© 2023 Society of Photo-Optical Instrumentation Engineers (SPIE)
Mark H. Cunningham, Peter Doel, David D. Brooks, Joar G. Brynnel, Roelof S. de Jong, Steffen Frey, Michael Schroeck, Miklos Gaebler, Daniel P. Sablowski, and Sam C. Barden "Assembly and alignment of the 4-metre multi-object spectroscopic telescope wide field corrector," Journal of Astronomical Telescopes, Instruments, and Systems 9(1), 015002 (14 February 2023). https://doi.org/10.1117/1.JATIS.9.1.015002
Received: 14 October 2022; Accepted: 25 January 2023; Published: 14 February 2023
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Cited by 1 scholarly publication.
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KEYWORDS
Lenses

Telescopes

Astronomical imaging

Optical alignment

Spectroscopy

Analog to digital converters

Field spectroscopy

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