The 4-metre Multi-Object Spectroscopic Telescope (4MOST) is a new wide-field, fibre-fed spectroscopic survey facility for the VISTA telescope at ESOs Paranal Observatory. The instrument enables the simultaneous acquisition of 2436 spectra across a 4.2 square deg field of view, using a tilting spine fibre positioner feeding three dedicated spectrographs. In this paper, we describe the calibration process, and performance verification of the Fibre-Target-Alignment (FTA) process for 4MOST. We show the complete FTA process, including calibration of the individual hardware- and software components. Namely the Metrology camera system, the Fibre Positioner AESOP, a spine based Secondary Guiding System, the sky to focal surface projection software, and residual minimization via raster scans. In total, the FTA system required one special tool, a large calibration target for the focal surface, and approximately 1 month of accumulated calibration work on the telescope. The FTA process reached approx. 24 um (0.4 arc sec) RMS distance between fibres and targets on sky about 3 weeks after installation of the final hardware components of 4MOST, which is when 4MOST had its first light event. By the time of writing this paper, i.e. 6 months later, we reach approx. 16 um (0.27 arc sec) RMS. Currently, we far exceed our requirements in terms of accuracy, and are doing trade-off studies to maximize scientific returns.

The 4-meter Multi-Object Spectroscopic Telescope (4MOST) instrument uses 2436 individually positioned optical fibres to couple the light of targets into its spectrographs. The Fibre Target Alignment (FTA) software controls all aspects of the 4MOST instrument that are involved to position the 2448 spines of the AESOP positioner to their target locations closer than 10 mu m RMS, within 90 seconds. The AESOP fibre positioner provides a HTML interface which is used by the FTA software to command spine movements. The metrology system consists of 4 cameras, and a sophisticated software package to measure the location of fibres, which are moved by the AESOP spines. Spines reach their target typically after 6 to 8 iterative movements, which are interlaced with metrology frames. The metrology software is capable of taking 4 images simultaneously, and reconstructing fibre positions to within 3 mu m RMS within 5 seconds. We present the FTA control software architecture, the interaction of sub-components and the different operation modes of the system. Especially the concurrent and simultaneous control of 4 metrology camera processes. Due to the complexity of the system, comprehensive debugging and visualization tools have been developed which allow a detailed understanding and interaction of the entire system. The graphical tool provides feedback for each individual camera stream and their combined result. It provides statistics and tools to manipulate individual spines, especially to recover them in case of entanglement. To develop the control software, a full end-to-end simulator has been created, which closes the loop between metrology image simulation, simulated fibre positioning and all control aspects in between. The metrology system uses the current spine position as presented by the AESOP positioner to render metrology camera images. Analysis and downstream computation is identical to the live software. When commanded to move spines, The AESOP simulator executes the identical steps to move spines, except sending electrical signals. After which it returns the expected spine positions after their move, which is taken as input for the next FTA iteration.

MOSAIC is the Multi-Object Spectrograph (MOS) for the 39m Extremely Large Telescope (ELT) of the European Southern Observatory (ESO), with unique capabilities in terms of multiplex, wavelength coverage and spectral resolution. It is a versatile multi-object spectrograph working in both the Visible and NIR domains, designed to cover the largest possible area (similar to 40 arcmin(2)) on the focal plane, and optimized to achieve the best possible signal-to-noise ratio on the faintest sources, from stars in our Galaxy to galaxies at the epoch of the reionization. In this paper we describe the main characteristics of the instrument, including its expected performance in the different observing modes. The status of the project will be briefly presented, together with the positioning of the instrument in the landscape of the ELT instrumentation. We also review the main expected scientific contributions of MOSAIC, focusing on the synergies between this instrument and other major ground-based and space facilities.

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.

The 4-metre Multi-Object Spectroscopic Telescope (4MOST) is a fibre-fed multi-object spectrograph for the VISTA telescope at the 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 degree field of view and consists of an optical Wide-Field Corrector (WFC), a fibre positioner system based on a tilting spine design, and three spectrographs giving both high and low spectral dispersion. The WFC comprises of 6 lenses grouped into 4 elements, 2 of which are cemented doublets that act as an atmospheric dispersion corrector (ADC). The first lens element is 0.9m in diameter whilst the diameter of the other elements is 0.65m. For the instrument to meet its science goals, each lens needs to be aligned to ∼50µm – a major challenge. This is achieved using contact metrology methods supplemented by pencil beam laser probes. In particular, a novel off-axis laser beam system has been implemented to test the optics’ alignment before and after shipment. This paper details the alignment and assembly methods and presents the latest results on the achieved lens positioning and projected performance of the WFC

The 4-meter Multi-Object Spectroscopic Telescope (4MOST) instrument uses 2436 individually positioned optical fibres to couple the light of targets into its spectrographs. The AESOP fibre positioner is mounted at the Cassegrain focus of the VISTA telescope, which houses the fibres in a hexagon-like structure with a diameter of 535 mm that covers a 2.5 deg diameter field of view on the sky. Fibres are positioned relative to fixed fiducial fibres. The metrology system determines the position of the fibres on the focal surface of the telescope relative to the fiducial fibres. The location of the fibres needs to be measured to better than 3 micron RMS in the focal surface, approximately 0.05 arc seconds on sky. Four imaging cameras are mounted on the VISTA spider vanes that look through the entire optical train, including primary and secondary mirror as well as the wide field corrector (WFC) / atmospheric dispersion compensator (ADC) unit. We recreated the setup for the metrology system in the lab with similar dynamic behavior but different optical design due to the lack of the VISTA telescope. We demonstrate the metrology system measurement accuracy in lab conditions on the full scale test stand. We also show how we measure distortions induced by optical path and the calibration procedure as a precursor for commissioning on the telescope. In particular, we present a method how to measure the surface shape of any optical surface with approx. 10 nm accuracy over its entire optically active surface.

A software tool which was designed to compute basic optical parameters of spectrographs is presented. The idea is to find a first layout of the spectrograph by focusing on the science goal to which the instrument needs to be adapted. We focus on systems used in astrophysical instrumentation. These include classical, 3D and echelle spectrographs. The code also computes efficiencies of the specified systems, expected signal-to-noise ratios, layout of the spectral orders on the detector, etc. Furthermore, a complete image seen by the detector can be simulated. This artificial data are used to compare the performance of different designs and to test data reduction pipelines, before the system is being physically build. Some additional tools are implemented to characterise special optical devices, for example the telescope-spectrograph-interface and to support the design process. Hence, SILENT is a pre-design tool to determine the required optical paraxial parameters of the system to meet the science application.

Spectangular is a GUI based software package written in C++ designed for spectral disentangling on the wavelength scale. The code disentangles spectra of SB1 and SB2 systems and can now also be used also for spectra showing variability. In this work, effects of variability caused by telluric lines, line profile, and continuum flux are being investigated. Also shown is the disentangling on spectra from an artificial eclipsing binary. It is now possible to optimize on the flux ratios of each spectrum, making the disentangling a technique for extracting photometric information from spectroscopic observations usually provided by additional photometry. Furthermore, we make some comments about changes to the code since it was first published.

Context. Capella (alpha Aur) is one of the few binaries in the sky with two cool giant stars. With spectral types of G8III and G0III, the two components appear at different but distinct stages in their evolution. The G0 secondary star is a Hertzsprung-gap giant, and the G8 primary star is thought to be a clump giant. Aims. We present a new measure of the carbon C-12/C-13 isotope ratio of the primary component of Capella using high-resolution R approximate to 250 000 spectra obtained with the Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) with both the Vatican Advanced Technology Telescope (VATT) and the Large Binocular Telescope (LBT). Methods. Signal-to-noise ratios of up to 2 700 were obtained by averaging nightly spectra. These average spectra were used to disentangle the two binary components. The isotope ratio was derived with the use of spectrum synthesis from the CN lines at 8004 angstrom. Results. We found that the C-12/C-13 ratio of the primary component of Capella is 17.8 +/- 1.9. Our measurement precision is now primarily limited by the spectral-line data and by the grid-step size of the model atmospheres rather than the data. The separated spectrum of the secondary component does not show distinguishable (CN)-C-12 and (CN)-C-13 lines because of its v sin i and higher temperature. Conclusions. Our new C-12/C-13 value is significantly lower than the previous value of 27 +/- 4 but now agrees better with the recent model prediction of 18.8-20.7.

Context. Capella (αAur) is one of the few binaries in the sky with two cool giant stars. With spectral types of G8III and G0III, the two components appear at different but distinct stages in their evolution. The G0 secondary star is a Hertzsprung-gap giant, and the G8 primary star is thought to be a clump giant.Aims. We present a new measure of the carbon12C/13C isotope ratio of the primary component of Capella using high-resolutionR ≈ 250 000 spectra obtained with the Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) with both the Vatican Advanced Technology Telescope (VATT) and the Large Binocular Telescope (LBT).Methods. Signal-to-noise ratios of up to 2 700 were obtained by averaging nightly spectra. These average spectra were used to disentangle the two binary components. The isotope ratio was derived with the use of spectrum synthesis from the CN lines at 8004 Å.Results. We found that the12C/13C ratio of the primary component of Capella is 17.8 ± 1.9. Our measurement precision is now primarily limited by the spectral-line data and by the grid-step size of the model atmospheres rather than the data. The separated spectrum of the secondary component does not show distinguishable12CN and13CN lines because of itsvsiniand higher temperature.Conclusions. Our new12C/13C value is significantly lower than the previous value of 27 ± 4 but now agrees better with the recent model prediction of 18.8–20.7.

Context. Capella (α Aur) is one of the few binaries in the sky with two cool giant stars. With spectral types of G8III and G0III, the two components appear at different but distinct stages in their evolution. The G0 secondary star is a Hertzsprung-gap giant, and the G8 primary star is thought to be a clump giant. Aims. We present a new measure of the carbon 12C/13C isotope ratio of the primary component of Capella using high-resolution R ≈250 000 spectra obtained with the Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) with both the Vatican Advanced Technology Telescope (VATT) and the Large Binocular Telescope (LBT). Methods. Signal-to-noise ratios of up to 2 700 were obtained by averaging nightly spectra. These average spectra were used to disentangle the two binary components. The isotope ratio was derived with the use of spectrum synthesis from the CN lines at 8004 Å. Results. We found that the 12C/13C ratio of the primary component of Capella is 17.8±1.9. Our measurement precision is now primarily limited by the spectral-line data and by the grid-step size of the model atmospheres rather than the data. The separated spectrum of the secondary component does not show distinguishable 12CN and 13CN lines because of its v sin i and higher temperature. Conclusions. Our new 12C/13C value is significantly lower than the previous value of 27±4 but now agrees better with the recent model prediction of 18.8 20.7.

The paper introduces the software Spectangular for spectral disentangling via singular value decomposition with global optimisation of the orbital parameters of the stellar system or radial velocities of the individual observations. We will describe the procedure and the different options implemented in our program. Furthermore, we will demonstrate the performance and the applicability using tests on artificial data. Additionally, we use high-resolution spectra of Capella to demonstrate the performance of our code on real-world data. The novelty of this package is the implemented global optimisation algorithm and the graphical user interface (GUI) for ease of use. We have implemented the code to tackle SB1 and SB2 systems with the option of also dealing with telluric (static) lines.