After completion of its final-design review last year, it is full steam ahead for the construction of the MOONS instrument - the next generation multi-object spectrograph for the VLT. This remarkable instrument will combine for the first time: the 8 m collecting power of the VLT, 1000 optical fibres with individual robotic positioners and both medium- and high-resolution spectral coverage acreoss the wavelength range 0.65μm - 1.8 μm. Such a facility will allow a veritable host of Galactic, Extragalactic and Cosmological questions to be addressed. In this paper we will report on the current status of the instrument, details of the early testing of key components and the major milestones towards its delivery to the telescope.
Following a successful Phase A study, we introduce the delivered conceptual design of the MOSAIC1 multi-object spectrograph for the ESO Extremely Large Telescope (ELT). MOSAIC will provide R~5000 spectroscopy over the full 460-1800 nm range, with three additional high-resolution bands (R~15000) targeting features of particular interest. MOSAIC will combine three operational modes, enabling integrated-light observations of up to 200 sources on the sky (high-multiplex mode) or spectroscopy of 10 spatially-extended fields via deployable integral-field units: MOAO6 assisted high-definition (HDM) and Visible IFUs (VIFU). We will summarise key features of the sub-systems of the design, e.g. the smart tiled focal-plane for target selection and the multi-object adaptive optics used to correct for atmospheric turbulence, and present the next steps toward the construction phase.
We present the consolidated scientific case for multi-object spectroscopy with the MOSAIC concept on the European ELT. The cases span the full range of ELT science and require either ‘high multiplex’ or ‘high definition’ observations to best exploit the excellent sensitivity and wide field-of-view of the telescope. Following scientific prioritisation by the Science Team during the recent Phase A study of the MOSAIC concept, we highlight four key surveys designed for the instrument using detailed simulations of its scientific performance. We discuss future ways to optimise the conceptual design of MOSAIC in Phase B, and illustrate its competitiveness and unique capabilities by comparison with other facilities that will be available in the 2020s.
Product Assurance is an essential activity to support the design and construction of complex instruments developed for major scientific programs. The international size of current consortia in astrophysics, the ambitious and challenging developments, make the product assurance issues very important. The objective of this paper is to focus in particular on the application of Product Assurance Activities to a project such as MOSAIC, within an international consortium. The paper will also give a general overview on main product assurance tasks to be implemented during the development from the design study to the validation of the manufacturing, assembly, integration and test (MAIT) process and the delivery of the instrument.
When combined with the huge collecting area of the ELT, MOSAIC will be the most effective and flexible Multi-Object Spectrograph (MOS) facility in the world, having both a high multiplex and a multi-Integral Field Unit (Multi-IFU) capability. It will be the fastest way to spectroscopically follow-up the faintest sources, probing the reionisation epoch, as well as evaluating the evolution of the dwarf mass function over most of the age of the Universe. MOSAIC will be world-leading in generating an inventory of both the dark matter (from realistic rotation curves with MOAO fed NIR IFUs) and the cool to warm-hot gas phases in z=3.5 galactic haloes (with visible wavelenth IFUs). Galactic archaeology and the first massive black holes are additional targets for which MOSAIC will also be revolutionary. MOAO and accurate sky subtraction with fibres have now been demonstrated on sky, removing all low Technical Readiness Level (TRL) items from the instrument. A prompt implementation of MOSAIC is feasible, and indeed could increase the robustness and reduce risk on the ELT, since it does not require diffraction limited adaptive optics performance. Science programmes and survey strategies are currently being investigated by the Consortium, which is also hoping to welcome a few new partners in the next two years.
The amplitudes and scales of spatial variations in the skylines can be a potential limit of the telescopes performance, because the study of the extremely faint objects requires a careful correction for the residual of the skylines if they are corrected. Using observations from the VLT/KMOS instrument, we have studied the spatial and temporal behavior of two faint skylines (10 to 80 times fainter than the strong skyline in the spectral window) and the effect of the skylines in the determination of the kinematics maps of distant galaxies. Using nine consecutives exposures of ten minutes. We found that the flux of the brighter skylines changes rapidly spatially and temporally, 5 to 10% and up to 15%, respectively. For the faint skyline, the fluctuations have a spatial and temporal amplitude up to 100%. The effect of the residual of the skyline on the velocity field of distant galaxies becomes dramatic when the emission line is faint (equivalent width equal to 15 A). All the kinematic information is lost. The shape and the centroid of the emission line change from spaxel to spaxel. This preliminary result needs to be extended; by continuing the simulation, in order to determine, the minimum flux that allows to recover of the kinematic information at different resolutions. Allowing to find the possible relation between spectral resolution and flux of the emission line. Our goal is to determine which is the best spectral resolution in the infrared to observe the distant galaxies with integral field spectrographs. Finding the best compromise between spectral resolution and the detection limit of the spectrograph.
We present a new scientific instrument simulator dedicated to the E-ELT named WEBSIM-COMPASS, and developed in the frame of the COMPASS project. This simulator builds on the previous series of WEBSIM simulators developed during the ESO E-ELT Design Reference Mission and Instrument Phase A studies. The WEBSIM-COMPASS observations simulator consists in a web interface coupled to an IDL code, which allows the user to perform end-to-end simulations of all E-ELT optical/NIR imagers and spectrographs foreseen for the future 39m European Extremely Large Telescope, i.e., MICADO, HARMONI, and MOSAIC. The simulation pipeline produces fake simulations in FITS format that mimic the result of a data reduction pipeline with perfectly extracted/reduced data. We give a functional description of this new simulator, emphasizing the new functionalities and current developments, and present science cases simulated used as test cases.
The main objective of the COMPASS project is to provide a full scale end-to-end AO development platform, able to address the E-ELT scale and designed as a free, open source numerical tool with a long term maintenance plan. The development of this platform is based on a full integration of software with hardware and relies on an optimized implementation on heterogeneous hardware using GPUs as accelerators. In this paper, we present the overall platform, the various work packages of this project, the milestones to be reached, the results already obtained and the first output of the ongoing collaborations.
We present simulated observations of one of the major science cases for the 39m E-ELT, namely the detection of very high-z galaxies. We simulated the detection of UV interstellar lines at z = 7 and the detection of the Lyman alpha line and the Lyman break at z = 9, both with MOAO-assisted IFUs and GLAO-fed fibers. These simulations are performed with the scientific simulator we developped in the frame of the E-ELT phase A studies. First, we give a functional description of this simulator, which is coupled to a public web interface WEBSIM, and we then give an example of its practical use to constrain the high level specifications of MOSAIC, a new multi-object spectrograph concept for the E-ELT. Our simulations show that the most constraining case is the detection of UV interstellar lines. The optimal pixel size is found to be ~80 mas, which allows detecting
UV lines up to JAB ~27 in 40 hours of integration time. Lyman Alpha Emitters and Lyman Break Galaxies are detected respectively up to JAB ~30 and JAB ~28 with a 80 mas/pixel IFU and within only 10 hours of integration time. Detection limits are typically ~0.5-1 mag fainter using MOAO-fed IFUs than using GLAO-fed fibers, but the multiplex is one magnitude larger in the mode using GLAO-fed fibers. We explore the optimal observational strategy for each observing mode considering these observing limits as well as the expected target densities.
Fiber-fed spectrographs can now have throughputs equivalent to slit spectrographs. However, the sky
subtraction accuracy that can be reached on such instruments has often been pinpointed as one of their major
issues, in relation to difficulties in scattered light and flat-field corrections or throughput losses associated
with fibers. Using technical time observations with FLAMES-GIRAFFE, two observing techniques, namely
dual staring and cross beam switching modes, were tested and the resulting sky subtraction accuracy reached
in both cases was quantified. Results indicate that an accuracy of 0.6% on the sky subtraction can be reached,
provided that the cross beam switching mode is used. This is very encouraging regarding the detection of very
faint sources with future fiber-fed spectrographs such as VLT/MOONS or E-ELT/MOSAIC.
The EAGLE and EVE Phase A studies for instruments for the European Extremely Large Telescope (E-ELT) originated
from related top-level scientific questions, but employed different (yet complementary) methods to deliver the required
observations. We re-examine the motivations for a multi-object spectrograph (MOS) on the E-ELT and present a unified
set of requirements for a versatile instrument. Such a MOS would exploit the excellent spatial resolution in the near-infrared envisaged for EAGLE, combined with aspects of the spectral coverage and large multiplex of EVE. We briefly
discuss the top-level systems which could satisfy these requirements in a single instrument at one of the Nasmyth foci of
The amplitudes and scales of spatial variations of the sky continuum background can be a potential limit of the telescope performance, because the study of the extremely faint objects requires the subtraction accuracy below 1%. Thus, studying its statistical properties is essential for the design of next generation instruments, especially the fiber-fed instruments, as well as their observation strategies. Using ESO archive data of VLT/FORS2 long-slit observations, we analyzed the auto-correlation function of the sky continuum. As preliminary results, we find that the sky continuum background has multi-scale spatial variations at scales from 2" to 150" with total amplitude of ~0.5%, for an given exposure time of 900s. This can be considered as the upper limit of sky continuum background variation over a field-of-view of few arcmins. The origin of these variations need further studies.
The detection and characterization of the physical properties of very distant galaxies will be one the prominent science case of all future Extremely Large Telescopes, including the 39m E-ELT. Multi-Object Spectroscopic instruments are potentially very important tools for studying these objects, and in particular fiber-based concepts. However, detecting and studying such faint and distant sources will require subtraction of the sky background signal (i.e., between OH airglow lines) with an accuracy of 1%. This requires a precise and accurate knowledge of the sky background temporal and spatial fluctuations. Using FORS2 narrow-band filter imaging data, we are currently investigating what are the fluctuations of the sky background at 9000A. We present preliminary results of sky background fluctuations from this study over spatial scales reaching 4 arcmin, as well as first glimpses into the temporal variations of such fluctuations over timescales of the order of the hour. This study (and other complementary on-going studies) will be essential in designing the next-generation fiber-fed instruments for the E-ELT.
We present preliminary results on on-sky test of sky subtraction methods for fiber-fed spectrograph. Using
dedicated observation with FLAMES/VLT in I-band, we have tested the accuracy of the sky subtraction for 4
sky subtraction methods: mean sky, closest sky, dual stare and cross-beam switching. The cross beam-switching
and dual stare method reach accuracy and precision of the sky subtraction under 1%. In contrast to the commonly
held view in the literature, this result points out that fiber-fed spectrographs are adapted for the observations
of faint targets.