4MOST, the 4m Multi Object Spectroscopic Telescope, is an upcoming 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, highenergy physics, galaxy evolution and cosmology. The preliminary design of 4MOST features 2436 fibres split into lowresolution (1624 fibres, 370-950 nm, R < 4000) and high-resolution spectrographs (812 fibres, three arms, ~44-69 nm coverage each, R < 18000) with a fibre positioner and covering an hexagonal field of view of ~4.1 deg<sup>2</sup>. The 4MOST consortium consists of several institutes in Europe and Australia under leadership of the Leibniz-Institut für Astrophysik Potsdam (AIP). 4MOST is currently in its Final Design Phase with an expected start of science operations in 2022. In this paper, the final optomechanical design and performances of 4MOST Low Resolution Spectrograph will be presented. It has been designed by CRAL for 4MOST FDR held in May, 2018. Special emphasis will be put on the technical requirements of individual optics and the mechanical design with its associated FEA.
A novel concept for the calibration of multi object fiber-fed spectrographs is described for the 4MOST instrument. The 4MOST facility is foreseen to start science operations in 2022 at the ESO VISTA telescope. The calibration system provides intensity, wavelength and resolution calibrations for the 4MOST spectrographs. The heart of the system is a combination of a bright broad band lamp and a Fabry-Perot etalon. The lamp is able to provide sufficient flux to illuminate the VISTA focal plane and the Fabry-Perot etalon provides a regular comb of spectral lines. The Fabry-Perot etalon can be moved in and out of the optical beam to choose between intensity and spectral calibrations. A fiber bundle of 156 fibers is guided to the VISTA spider arms where each fiber is connected to a small integrating sphere. The integrating spheres are attached to the bottom side of the four VISTA telescope spider struts and provide unvignetted illumination of the telescope. The exit port of the integrating spheres is projected on the VISTA focal plane with a small collimator lens. The integrating spheres assure a uniform illumination of the focal plane and are insensitive to FRD effects of the input fibers due to motion and stress during telescope movements. The calibration system illumination only originates from the telescope spiders and therefore the telescope pupil is not fully filled. The calibration system uses the azimuthal scrambling properties of the fibers that connect the telescope focal plane and the spectrometers to completely fill the spectrograph pupil.
The 4-metre Multi-Object Spectroscopic Telescope (4MOST) instrument uses 2436 individually positioned optical fibres to couple the light of targets into its spectrographs. TOAD, the "Top Of the Atmosphere to Detector" simulator, is a primary engineering tool that accompanies the development of the 4MOST instrument. The tool provides a detailed, end-to-end performance model both in terms of throughput and image quality for 4MOST. Its results are used for system performance analysis, data reduction pipeline development and to generate input data for other simulation tools of the project.
The 4-metre Multi-Object Spectroscopic Telescope (4MOST) instrument uses 2436 individually positioned optical fibres to couple the light of targets into its spectrographs. The metrology system determines the position of the back-illuminated fibres on the focal surface of the telescope. It consists of 4 identical cameras that are mounted on the spider vanes of the secondary mirror of the VISTA telescope and look through the entire optical train, including M1, M2 and the WFC/ADC unit. Here, we present an exhaustive study on the expected centroiding errors, including but not limited to lens fabrication errors, seeing, mirror distortions and parallax effects.
With more than 200 scientists and engineers involved, the design and manufacture of the 4MOST instrument, a secondgeneration spectroscopic instrument built for ESO's 4.1-metre VISTA telescope, is a challenge requiring the implementation of an efficient quality assurance strategy during each project phase (i.e., design, manufacture, test, installation, and operation), and including the maintenance. This paper introduces the 4MOST product assurance approach used by the project to make sure that 4MOST will comply with all necessary quality and safety requirements over the whole instrument’s lifetime of 15 years. For quality assurance, the guiding principles are mainly given by the ISO 10007:2017 and ISO 9001:2015 quality management standards. Related to safety, 4MOST design and manufacture complies not only with the essential safety requirements from the European Union New Approach Directives (CE Marking Directives), but also with the additional requirements coming from the ESO Safety Policy, issued by the ESO Management for ESO-wide application. The implementation of the 4MOST project’s Quality Assurance and Configuration Management is described in detail in the paper.
We present an overview and status update of the 4MOST project at the Final Design Review. 4MOST is a major new wide-field, high-multiplex spectroscopic survey facility under development for the VISTA telescope at the Paranal Observatory of ESO. Starting in 2022, 4MOST will deploy 2436 optical fibres in a 4.1 square degree field-of-view using a fibre positioner based on the tilting spine principle. The fibres will feed one high-resolution (R~20,000) and two low-resolution (R~5000) spectrographs that all have fixed configuration, 3-channel designs with identical 6k x 6k CCD detectors. Updated performance estimates will be presented based on components already manufactured and pre-production prototypes of critical subsystems.
The 4MOST science goals are mostly driven by a number of large area, space-based observatories of prime European interest: Gaia and PLATO (Galactic Archeology and Stellar Physics), eROSITA (High-Energy Sky), and Euclid (Cosmology and Galaxy Evolution). Science cases based on these observatories, along with wide-area ground-based facilities such as LSST, VISTA and VST drive the ten Consortium Surveys covering a large fraction of the Southern sky, with bright time mostly devoted to the Milky Way disk and bulge areas and the Magellanic Clouds, and the dark/gray time largely devoted to extra-galactic targets. In addition there will be a significant fraction of the fibre-hours devoted to Community Surveys, making 4MOST a true general-purpose survey facility, capable of delivering spectra of samples of objects that are spread over a large fraction of the sky.
The 4MOST Facility Simulator was created to show the feasibility of the innovative operations scheme of 4MOST with all surveys operating in parallel. The simulator uses the mock catalogues created by the science teams, simulates the spectral throughput and detection of the objects, assigns the fibres at each telescope pointing, creates pointing distributions across the sky and simulates a 5-year survey (including overhead, calibration and weather losses), and finally does data quality analyses and computes the science Figure-of-Merits to assess the quality of science produced. The simulations prove the full feasibility of running different surveys in parallel.
The 4-meter Multi-Object Spectroscopic Telescope (4MOST) is a wide-field, high-multiplex spectroscopic survey facility under development for the Visible and Infrared Survey Telescope for Astronomy (VISTA) 4 meter telescope of the European Southern Observatory (ESO) at Cerro Paranal. The objective of 4MOST is to enable the simultaneous spectroscopy of a significant number of targets within a 2.5° diameter field of view, to allow high-efficiency all-sky spectroscopic surveys. A wide field corrector (WFC) is needed to couple targets across the 2.5° field diameter with the exit pupil concentric with the spherical focal surface where ~2400 fibres are configured by a fibre positioner (AESOP). For optimal fibre optic coupling and active optics wavefront sensing the WFC will correct optical aberrations of the primary (M1) and secondary (M2) VISTA optics across the full field of view and provide a well-defined and stable focal surface to which the acquisition/guiding sensors, wavefront sensors, and fibre positioner are interfaced. It will also compensate for the effects of atmospheric dispersion, allowing good chromatic coupling of stellar images with the fibre apertures over a wide range of telescope zenith angles (ZD). The fibres feed three spectrographs; two thirds of the fibres will feed two low resolution spectrographs and the remaining 812 fibres will feed a high-resolution spectrograph. The three spectrographs are fixed-configuration with three channels each. We present the 4MOST optical system together with optical simulation of subsystems.
The 4MOST Facility is a high-multiplex, wide-field, brief-fed spectrograph system for the ESO VISTA telescope. It aims to create a world-class spectroscopic survey facility unique in its combination of wide-field multiplex, spectral resolution, spectral coverage, and sensitivity. At the end of 2014, after a successful concept optimization design phase, 4MOST entered into its Preliminary Design Phase. Here we present the process and tools adopted during the Preliminary Design Phase to define the subsystems specifications, coordinate the interface control documents and draft the system verification procedures.
We present an overview of the 4MOST project at the Preliminary Design Review. 4MOST is a major new wide-field, high-multiplex spectroscopic survey facility under development for the VISTA telescope of ESO. 4MOST has a broad range of science goals ranging from Galactic Archaeology and stellar physics to the high-energy physics, galaxy evolution, and cosmology. Starting in 2021, 4MOST will deploy 2436 fibres in a 4.1 square degree field-of-view using a positioner based on the tilting spine principle. The fibres will feed one high-resolution (R~20,000) and two medium resolution (R~5000) spectrographs with fixed 3-channel designs and identical 6k x 6k CCD detectors. 4MOST will have a unique operations concept in which 5-year public surveys from both the consortium and the ESO community will be combined and observed in parallel during each exposure. The 4MOST Facility Simulator (4FS) was developed to demonstrate the feasibility of this observing concept, showing that we can expect to observe more than 25 million objects in each 5-year survey period and will eventually be used to plan and conduct the actual survey.
4MOST, the 4m Multi Object Spectroscopic Telescope, is an upcoming 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, highenergy physics, galaxy evolution and cosmology. The preliminary design of 4MOST features 2436 fibres split into lowresolution (1624 fibres, 370-950 nm, R > 4000) and high-resolution spectrographs (812 fibres, three arms, ~44-69 nm coverage each, R >18000) with a fibre positioner and covering an hexagonal field of view of ~4.1 deg<sup>2</sup>. The 4MOST consortium consists of several institutes in Europe and Australia under leadership of the Leibniz-Institut für Astrophysik, Potsdam (AIP). 4MOST is currently in its Preliminary Design Phase with an expected start of science operations in 2021. Two third of fibres go to two Low Resolution Spectrographs with three channels per spectrograph. Each low resolution spectrograph is composed of 812 scientific and 10 calibration fibres using 85μm core fibres at f/3, a 200mm beam for an off-axis collimator associated to its Schmidt corrector, 3 arms with f/1.73 cameras and standard 6k x 6k 15μm pixel detectors. CRAL has the responsibility of the Low Resolution Spectrographs. In this paper, the optical design and performances of 4MOST Low Resolution Spectrograph designed for 4MOST PDR in June, 2016 will be presented. Special emphasis will be put on the Low Resolution Spectrograph system budget and performance analysis.