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 μm 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.

HARMONI is the ELT's first light visible and near-infrared (0.5 to 2.45 mu m) integral field spectrograph over a range of resolving powers from R similar to 3500 to R similar to 18000. It will provide 4 different spatial scales from 4*4mas to 30*60mas. It can operate in two Adaptive Optics (AO) modes - Single Conjugate AO (including a High Contrast capability) and Laser Tomography AO - or with No AO. The project is preparing for Final Design Reviews. The Integral Field Spectrograph (IFS) is the science instrument operating at 130K. This paper depicts the test tools developed to validate one sub-system, the Integral Field Unit (IFU), developed in Centre de Recherche Astrophysique de Lyon. The IFU is in charge of splitting, slicing and rearranging the rectangular field of view into 4 long slits (similar to 540mm) to feed the 4 spectrographs. The tools are measuring position, angular deviation, wavefront or geometry of the field at ambient and operating temperature. Their design and validation are described with measurements on prototypes in our test cryostat. Their use for the final validation of the IFU performances is also addressed.

HARMONI is the first light visible and near-IR integral field spectrograph for the ELT. It covers a large spectral range from 450 nm to 2450 nm with resolving powers from 3500 to 18000 and spatial sampling from 60 mas to 4 mas. It can operate in two Adaptive Optics modes - SCAO (including a High Contrast capability) and LTAO - or with NOAO. The project is preparing for Final Design Reviews. HARMONI is a work-horse instrument that provides efficient, spatially resolved spectroscopy of extended objects or crowded fields of view. The gigantic leap in sensitivity and spatial resolution that HARMONI at the ELT will enable promises to transform the landscape in observational astrophysics in the coming decade. The project has undergone some key changes to the leadership and management structure over the last two years. We present the salient elements of the project restructuring, and modifications to the technical specifications. The instrument design is very mature in the lead up to the final design review. In this paper, we provide an overview of the instrument's capabilities, details of recent technical changes during the red flag period, and an update of sensitivities.

HARMONI is the first light visible and near-IR integral field spectrograph for the ELT. It covers a large spectral range from 470nm to 2450nm with resolving powers from 3300 to 18000 and spatial sampling from 60mas to 4mas. It can operate in two Adaptive Optics modes - SCAO (including a High Contrast capability) and LTAO - or with NOAO. The project is preparing for Final Design Reviews. From the perspective of data reduction, HARMONI introduces unique challenges due to its multiple adaptive optics modes, four spatial scales, eleven gratings, and two distinct NIR detector read-out modes. Capitalizing upon CRAL's experience in developing instrument simulators, this complexity prompted the development of the HARMONI Instrument Numerical Model (HINM). Built upon standard astrophysical Python frameworks, this software uses the Fourier optics concept to propagate a wavefront through the instrument, and leverages existing simulation tools for adaptive optics, sky and detector simulation. This enables the generation of synthetic detector read-outs for both calibration and science exposures. This paper highlights the crucial role played by the HINM simulator to develop the data reduction pipeline and elaborate instrument calibration procedures.

The PIC (Photogrammetry Inside Cryostat) is a cutting-edge periscope designed to be used during the prototyping, testing and alignment phase of HARMONI, one of the first-generation instruments of the Extremely Large Telescope. The challenge posed by operating the HARMONI instrument at a temperature of 130 K required the development of different non-contact measurement techniques to qualify optical and mechanical parts without touching them. Photogrammetry is a non-contact measurement technique, but it needed to be adapted to be used in a cryostat; this led to the development of the PIC. The periscope consists of a combination of six lenses, two mirrors, and three motorized degrees of freedom (the whole is mounted upside down on the lid of the test cryostat at CRAL in Lyon) and work together with an external camera to capture images at various angles. This is essential for obtaining accurate photogrammetric measurements. The motorized rotation systems allow for precise and controlled movements, and the combination of lenses and mirrors ensure that the images captured by the external camera are of the highest quality. The goal of the PIC is to obtain an accuracy of 25 μm + 5 μm, making it an essential component of the HARMONI tools and a major advancement in cryogenic photogrammetry.

HARMONI is the first light, adaptive optics assisted, integral field spectrograph for the European Southern Observatory’s Extremely Large Telescope (ELT). A work-horse instrument, it provides the ELT’s diffraction limited spectroscopic capability across the near-infrared wavelength range. HARMONI will exploit the ELT’s unique combination of exquisite spatial resolution and enormous collecting area, enabling transformational science. The design of the instrument is being finalized, and the plans for assembly, integration and testing are being detailed. We present an overview of the instrument’s capabilities from a user perspective, and provide a summary of the instrument’s design. We also include recent changes to the project, both technical and programmatic, that have resulted from red-flag actions. Finally, we outline some of the simulated HARMONI observations currently being analyzed.

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.

The processing of raw data from modern astronomical instruments is often carried out nowadays using dedicated software, known as pipelines, largely run in automated operation. In this paper we describe the data reduction pipeline of the Multi Unit Spectroscopic Explorer (MUSE) integral field spectrograph operated at the ESO Paranal Observatory. This spectrograph is a complex machine: it records data of 1152 separate spatial elements on detectors in its 24 integral field units. Efficiently handling such data requires sophisticated software with a high degree of automation and parallelization. We describe the algorithms of all processing steps that operate on calibrations and science data in detail, and explain how the raw science data is transformed into calibrated datacubes. We finally check the quality of selected procedures and output data products, and demonstrate that the pipeline provides datacubes ready for scientific analysis.

HARMONI is the adaptive optics assisted, near-infrared and visible light integral field spectrograph for the Extremely Large Telescope (ELT). A first light instrument, it provides the work-horse spectroscopic capability for the ELT. As the project approaches its Final Design Review milestone, the design of the instrument is being finalized, and the plans for assembly, integration and testing are being detailed. We present an overview of the instrument’s capabilities from a user perspective, provide a summary of the instrument’s design, including plans for operations and calibrations, and provide a brief glimpse of the predicted performance for a specific observing scenario. The paper also provides some details of the consortium composition and its evolution since the project commenced in 2015.

HARMONI is the first light visible and near-IR integral field spectrograph for the ELT. It covers a large spectral range from 450nm to 2450nm with resolving powers from R (≡λ/Δλ) 3500 to 18000 and spatial sampling from 60mas to 4mas. It can operate in two Adaptive Optics modes - SCAO (including a High Contrast capability) and LTAO - or with NOAO. The project is preparing for Final Design Reviews. HARMONI slices the input light beam in subfields and then into slitlets and rearranges them to obtain spectra on its detectors. The Data Reduction software (DRS) handles calibration and scientific raw data from HARMONI and computes a fully reduced and calibrated science data cube. The challenge is to develop robust methods suitable for each of the 44 scale/band combinations of HARMONI. The geometrical calibration, one of the steps of the DRS, determines the coordinate transformation from detector pixels to wavelength and relative spatial position in the input focal plane. This paper provides a mathematical description of the algorithms involved in the geometrical calibration and presents validations on mock data simulated with the HARMONI Instrument Numerical Model (HINM). Briefly, to cope with a possible overlap of slitlets, we locate the slitlets using a global fitting method on flat-field exposures. The wavelength solution is computed using arc exposures. To compute the geometrical transformation we choose to use specific masks illuminated with a white continuum lamp. A trace mask exposure provides the transformation along the slitlets. A pinhole mask exposure determines the transformation in the perpendicular direction by fitting the flux within each slitlet.

JWST/NIRSpec will be the first multi-object spectrograph (MOS) to fly in space and it will enable the simultaneous measurement of up to similar to 200 spectra over the wavelength range similar to 0.6 - 5.3 mu m, allowing us to study the rest-frame optical properties of large samples of galaxies out to z similar to 9, and the rest-frame UV out to z > 10. To support the community in preparing NIRSpec MOS programs and getting ready to analyze the data, we present here a set of simulations closely mimicking the deep spectroscopic observations that will be performed as part of the JADES survey, a joint effort of the NIRCam and NIRSpec GTO teams. The simulations are made possible by the NIRSpec Instrument Performance Simulator software, a Fourier Optics wave propagation module coupled with a detailed model of the instruments optical geometry and radiometric response, and a detector simulator reproducing the noise properties and response of NIRSpec's two H2RG sensors. The targets for the simulations were selected from the JWST Extragalactic Mock Catalog, JAGUAR. The simulation data package delivered here include more than 60 count-rate images corresponding to the exposures break-down of the low and medium resolution part of one of the two NIRSpec deep-field spectroscopic programs of the JADES survey. The simulated data consists of three dither pointings, for 4 different instrument configurations (low and medium resolution over the entire NIRSpec wavelength range), plus the extracted, background subtracted, spectral traces for each of the 370 targets and corresponding 2D-rectified spectra and calibrated 1D spectra, as well as the mock astronomical data used as the simulation input.

This paper introduces the science software of HARMONI. The Instrument Numerical Model simulates the instrument from the optical point of view and provides synthetic exposures simulating detector readouts from data-cubes containing astrophysical scenes. The Data Reduction Software converts raw-data frames into a fully calibrated, scientifically usable data cube. We present the functionalities and the preliminary design of this software, describe some of the methods and algorithms used and highlight the challenges that we will have to face.

HARMONI is the E-ELT’s first light visible and near-infrared integral field spectrograph. It will provide four different spatial scales, ranging from coarse spaxels of 60 × 30 mas best suited for seeing limited observations, to 4 mas spaxels that Nyquist sample the diffraction limited point spread function of the E-ELT at near-infrared wavelengths. Each spaxel scale may be combined with eleven spectral settings, that provide a range of spectral resolving powers (R ~3500, 7500 and 20000) and instantaneous wavelength coverage spanning the 0.5 – 2.4 μm wavelength range of the instrument. In autumn 2015, the HARMONI project started the Preliminary Design Phase, following signature of the contract to design, build, test and commission the instrument, signed between the European Southern Observatory and the UK Science and Technology Facilities Council. Crucially, the contract also includes the preliminary design of the HARMONI Laser Tomographic Adaptive Optics system. The instrument’s technical specifications were finalized in the period leading up to contract signature. In this paper, we report on the first activity carried out during preliminary design, defining the baseline architecture for the system, and the trade-off studies leading up to the choice of baseline.

HARMONI is a visible and near-infrared integral field spectrograph designed to be a first-light instrument on the European extremely large telescope. It will use both single-conjugate and laser tomographic adaptive optics to fully exploit high-performance and sky coverage. Using a fast AO modelling toolbox, we simulate anisoplanatism effects on the point spread function of the single-conjugate adaptive optics of HARMONI. We investigate the degradation of the correction performance with respect to the off-axis distance in terms of Strehl ratio and ensquared energy. In addition, we analyse what impact the natural guide source magnitude, AO sampling frequency and number of sub-apertures have on performance.We show, in addition to the expected PSF degradation with the field direction, that the PSF retains a coherent core even at large off-axis distances. We demonstrated the large performance improvement of fine tuning the sampling frequency for dimer natural guide stars and an improvement of approx. 50% in SR can be reached above the nominal case. We show that using a smaller AO system with only 20x20 sub-apertures it is possible to further increase performance and maintain equivalent performance even for large off-axis angles.

MUSE (Multi Unit Spectroscopic Explorer) is a second generation Very Large Telescope (VLT) integral field spectrograph developed for the European Southern Observatory (ESO). It combines a 1’ x 1’ field of view sampled at 0.2 arcsec for its Wide Field Mode (WFM) and a 7.5"x7.5" field of view for its Narrow Field Mode (NFM). Both modes will operate with the improved spatial resolution provided by GALACSI (Ground Atmospheric Layer Adaptive Optics for Spectroscopic Imaging), that will use the VLT deformable secondary mirror and 4 Laser Guide Stars (LGS) foreseen in 2015. MUSE operates in the visible wavelength range (0.465-0.93 μm). A consortium of seven institutes is currently commissioning MUSE in the Very Large Telescope for the Preliminary Acceptance in Chile, scheduled for September, 2014. MUSE is composed of several subsystems which are under the responsibility of each institute. The Fore Optics derotates and anamorphoses the image at the focal plane. A Splitting and Relay Optics feed the 24 identical Integral Field Units (IFU), that are mounted within a large monolithic structure. Each IFU incorporates an image slicer, a fully refractive spectrograph with VPH-grating and a detector system connected to a global vacuum and cryogenic system. During 2012 and 2013, all MUSE subsystems were integrated, aligned and tested to the P.I. institute at Lyon. After successful PAE in September 2013, MUSE instrument was shipped to the Very Large Telescope in Chile where that was aligned and tested in ESO integration hall at Paranal. After, MUSE was directly transported, fully aligned and without any optomechanical dismounting, onto VLT telescope where the first light was overcame the 7th of February, 2014. This paper describes the alignment procedure of the whole MUSE instrument with respect to the Very Large Telescope (VLT). It describes how 6 tons could be move with accuracy better than 0.025mm and less than 0.25 arcmin in order to reach alignment requirements. The success of the MUSE alignment is demonstrated by the excellent results obtained onto MUSE image quality and throughput directly onto the sky.

MUSE, a giant integral field spectrograph, is about to become the newest facility instrument at the VLT. It will see first light in February 2014. Here, we summarize the properties of the instrument as built and outline functionality of the data reduction system, that transforms the raw data that gets recorded separately in 24 IFUs by 4k CCDs, into a fully calibrated, scientifically usable data cube. We then describe recent work regarding geometrical calibration of the instrument and testing of the processing pipeline, before concluding with results of the Preliminary Acceptance in Europe and an outlook to the on-sky commissioning.

HARMONI is a visible and near-infrared (0.47 to 2.45 μm) integral field spectrometer, providing the E-ELT's core spectroscopic capability, over a range of resolving powers from R (≡λ/Δλ)~500 to R~20000. The instrument provides simultaneous spectra of ~32000 spaxels at visible and near-IR wavelengths, arranged in a √2:1 aspect ratio contiguous field. HARMONI is conceived as a workhorse instrument, addressing many of the E-ELT’s key science cases, and will exploit the E-ELT's scientific potential in its early years, starting at first light. HARMONI provides a range of spatial pixel (spaxel) scales and spectral resolving powers, which permit the user to optimally configure the instrument for a wide range of science programs; from ultra-sensitive to diffraction limited, spatially resolved, physical (via morphology), chemical (via abundances and line ratios) and kinematic (via line-of-sight velocities) studies of astrophysical sources. Recently, the HARMONI design has undergone substantial changes due to significant modifications to the interface with the telescope and the architecture of the E-ELT Nasmyth platform. We present an overview of the capabilities of HARMONI, and of its design from a functional and performance viewpoint.

MUSE (Multi Unit Spectroscopic Explorer) is a second generation Very Large Telescope (VLT) integral field spectrograph (1x1arcmin(2) Field of View) developed for the European Southern Observatory (ESO), operating in the visible wavelength range (0.465-0.93 mu m). A consortium of seven institutes is currently commissioning MUSE in the Very Large Telescope for the Preliminary Acceptance in Chile, scheduled for September, 2014.MUSE is composed of several subsystems which are under the responsibility of each institute. The Fore Optics derotates and anamorphoses the image at the focal plane. A Splitting and Relay Optics feed the 24 identical Integral Field Units (IFU), that are mounted within a large monolithic instrument mechanical structure. Each IFU incorporates an image slicer, a fully refractive spectrograph with VPH-grating and a detector system connected to a global vacuum and cryogenic system. During 2012 and 2013, all MUSE subsystems were integrated, aligned and tested to the P.I. institute at Lyon. After successful PAE in September 2013, MUSE instrument was shipped to the Very Large Telescope in Chile where that was aligned and tested in ESO integration hall at Paranal. After, MUSE was directly transferred in monolithic way without dismounting onto VLT telescope where the first light was overcame.This talk describes the IFU Simulator which is the main alignment and performance tool for MUSE instrument. The IFU Simulator mimics the optomechanical interface between the MUSE pre-optic and the 24 IFUs. The optomechanical design is presented. After, the alignment method of this innovative tool for identifying the pupil and image planes is depicted. At the end, the internal test report is described. The success of the MUSE alignment using the IFU Simulator is demonstrated by the excellent results obtained onto MUSE positioning, image quality and throughput. MUSE commissioning at the VLT is planned for September, 2014.

MUSE Instrumentation Software is the software devoted to the control of the Multi-Unit Spectroscopic Explorer (MUSE), a second-generation VLT panoramic integral-field spectrograph instrument, installed at Paranal in January 2014. It includes an advanced and user-friendly GUI to display the raw data of the 24 detectors, as well as the on-line reconstructed images of the field of view allowing users to assess the quality of the data in quasi-real time. Furthermore, it implements the slow guiding system used to remove effects of possible differential drifts between the telescope guide probe and the instrument, and reach high image stability (<0.03 arcsec RMS stability).In this paper we report about the software design and describe the developed tools that efficiently support astronomers while operating this complex instrument at the telescope.

MUSE, the Multi Unit Spectroscopic Explorer,1 is an integral-field spectrograph under construction for the ESO VLT to see first light in 2013. It can record spectra of a 1′x1′ field on the sky at a sampling of 0″.2x0″.2, over a wavelength range from 4650 to 9300Å. The data reduction for this instrument is the process which converts raw data from the 24 CCDs into a combined datacube (with two spatial and one wavelength axis) which is corrected for instrumental and atmospheric effects. Since the instrument consists of many subunits (24 integral-field units, each slicing the light into 48 parts, i. e. 1152 regions with a total of almost 90000 spectra per exposure), this task requires many steps and is computationally expensive, in terms of processing speed, memory usage, and disk input/output. The data reduction software is designed to be mostly run as an automated pipeline and to fit into the open source environment of the ESO data flow as well as into a data management system based on AstroWISE. We describe the functionality of the pipeline, highlight details of new and unorthodox processing steps, discuss which algorithms and code could be used from other projects. Finally, we show the performance on both laboratory data as well as simulated scientific data.