MOSAIC is a multi-object spectrograph planned to be installed on the ESO-Extremely Large Telescope. The project is approved to start its phase B in September/October 2022. The main science cases addressed by MOSAIC go from the study of faint stars in the Milky Way and in the local group, to the study of dark matter, galaxy evolution and first-light objects at the epoch of reionisation. The MOSAIC instrument offers Multi-Object Spectroscopy and Integral Field Units capabilities from the visible (VIS) to the near-infrared (NIR). The Laboratoire d’Astrophysique de Marseille is responsible for the development of the near infrared spectrograph. More precisely, it is in charge of the global architecture and design of the NIR spectrograph (optical, mechanical, thermal) and the assembly, integration, tests and verification (AIT/V) activities in cryogenic environment. In this article, the main tradeoffs in terms of optical and mechanical architectures are analyzed; the main technical choices are justified according to the science requirements (from which technical requirement specifications are derived) and the level of maturity of key critical technologies. The NIR spectrograph will be described in terms of system engineering approach. The requirement flow-down strategy, from high-level requirements at the system level toward technical specifications at the module and component levels will be presented. The main interfaces and the development philosophy (with an emphasis on the AIT/V plan) will also be included.
MOSAIC, the multi-object spectrograph (MOS) for the ESO 39m European Extremely Large Telescope (ELT), will combine visible and near-infrared observations with multi-object and multi-integral field spectroscopy capabilities. It will cover a wide panel of topics, from resolved stars up to the most distant galaxies. In the frame of the NIR spectrograph unit realization led by the Laboratoire d’Astrophysique de Marseille (LAM), this paper presents the ongoing development of a cryogenic (90-130 K) NIR camera prototype tested in the 0.77-1.063 µm wavelengths (I band) detailing the opto-mechanical design and the integration and verification strategies in accordance with validation in relevant environment (ESO TRL5).
MOSAIC is the Multi-Object Spectrograph for the ESO Extremely Large Telescope, approved to enter Phase B beginning 2022. It is conceived as a multi- purpose instrument covering the Visible and Near Infrared bandwidth (0.45 –1.8 μm) with two observing modes: spatially resolved spectroscopy with 8 integral field units; and the simultaneous observation of 200 objects in the VIS and NIR in unresolved spectroscopy.
We present an overview of the main MOSAIC science drivers and the actual baseline design for the instrument. The prototyping and developments undertaken by the consortium to evaluate the feasibility of the project are also discussed.
MOSAIC is the Muti-Object Spectrograph for the ESO Extremely Large Telescope. The Laboratoire d’Astrophysique de Marseille (LAM) is in charge of the instrument “Assembly, Integration, Test and Verification (AIT/V)” phases. AITV for AO instruments, in laboratory as in the telescope, always represent numerous technical challenges. We already started the preparation and planning for the instrument level AIT activities, from identification of needs, challenges, risks, to defining the optimal AIT strategy. In this paper, we present the state of this study and describe several AIT/V scenarios and a planning for AIT phases in Europe and in Chile. We also show our capacity, experience and expertise to lead the instrument MOSAIC AIT/V activities.
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.
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.
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.
S4EI (Spectral Sampling with Slicer for Stellar and Extragalactical Instrumentation) is a new concept for extending Multichannel Subtractive Double Pass (ie S4I - Spectral Sampling with Slicer for Solar Instrumentation) to night-time astronomy. The Multichannel Subtractive Double Pass (MSDP) spectrographs have been widely used in solar spectroscopy because of their ability to provide an excellent compromise between field of view and the spatial and spectral resolutions. Compared with other spectrographs, MSDP can deliver simultaneous monochromatic images without any time-scanning requirements (as the standard Fabry-Perot), with limited loss of flux. Spatial resolution is the same as for an Imager given by the telescope: it can be very high. It is based on new generation reflecting plane image slicers working with large apertures specific to night-time telescopes. The resulting design could be potentially very attractive and innovative for different domains of astronomy, e.g., the simultaneous spatial mapping of accurately flux-calibrated emission lines between OH sky lines in extragalactic astronomy or the simultaneous imaging of stars, exoplanets and interstellar medium. The determination of physical and chemical properties of galaxies needs to observe several emission lines at different wavelengths. The combination of these lines gives access to the distribution in dust, star formation rate, metallicity, the kinematics or even to the electron density of the gas in the galaxies. The spatial resolution of MSDP allows, like the 3D or integral field spectrographs the construction of spatial distribution maps. The advantage of S4EI is that by measuring simultaneously the different lines, the relative errors of the flux calibration between the different wavelengths of the lines are potentially limited by the uncertainty of the calibration source used, which is expected to significantly reduce the associated errors and thus increase the precision and accuracy of estimates.
In the era of Extremely Large Telescopes, the current generation of 8-10m facilities are likely to remain competitive at far-blue visible wavelengths for the foreseeable future. High-efficiency (<20%) observations of the ground UV (300- 400 nm) at medium resolving power (R~20,000) are required to address a number of exciting topics in stellar astrophysics, while also providing new insights in extragalactic science. Anticipating strong demand to better exploit this diagnostic-rich wavelength region, we revisit the science case and instrument requirements previously assembled for the CUBES concept for the Very Large Telescope.
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.
KEYWORDS: Adaptive optics, Spectrographs, Telescopes, James Webb Space Telescope, Adaptive optics, Galactic astronomy, Molybdenum, K band, Space telescopes, Near infrared, Spectral resolution
There are 8000 galaxies, including 1600 at z ≥ 1.6, which could be simultaneously observed in an E-ELT field of view of 40 arcmin2. A considerable fraction of astrophysical discoveries require large statistical samples, which can only be obtained with multi-object spectrographs (MOS). MOSAIC will provide a vast discovery space, enabled by a multiplex of 200 and spectral resolving powers of R=5000 and 20000. MOSAIC will also offer the unique capability of more than 10 `high-definition' (multi-object adaptive optics, MOAO) integral-field units, optimised to investigate the physics of the sources of reionization. The combination of these modes will make MOSAIC the world-leading MOS facility, contributing to all fields of contemporary astronomy, from extra-solar planets, to the study of the halo of the Milky Way and its satellites, and from resolved stellar populations in nearby galaxies out to observations of the earliest ‘first-light’ structures in the Universe. It will also study the distribution of the dark and ordinary matter at all scales and epochs of the Universe. Recent studies of critical technical issues such as sky-background subtraction and MOAO have demonstrated that such a MOS is feasible with state-of-the-art technology and techniques. Current studies of the MOSAIC team include further trade-offs on the wavelength coverage, a solution for compensating for the non-telecentric new design of the telescope, and tests of the saturation of skylines especially in the near-IR bands. In the 2020s the E-ELT will become the world's largest optical/IR telescope, and we argue that it has to be equipped as soon as possible with a MOS to provide the most efficient, and likely the best way to follow-up on James Webb Space Telescope (JWST) observations.
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.
We present a discussion of the design issues and trade-offs that have been considered in putting together a new concept for MOSAIC,1, 2 the multi-object spectrograph for the E-ELT. MOSAIC aims to address the combined science cases for E-ELT MOS that arose from the earlier studies of the multi-object and multi-adaptive optics instruments (see MOSAIC science requirements in [3]). MOSAIC combines the advantages of a highly-multiplexed instrument targeting single-point objects with one which has a more modest multiplex but can spatially resolve a source with high resolution (IFU). These will span across two wavebands: visible and near-infrared.
KEYWORDS: Space telescopes, Spectrographs, Spectroscopes, Telescopes, Galactic astronomy, K band, Spectral resolution, James Webb Space Telescope, Visible radiation, Sensors
Building on the comprehensive White Paper on the scientific case for multi-object spectroscopy on the European ELT, we present the top-level instrument requirements that are being used in the Phase A design study of the MOSAIC concept. The assembled cases span the full range of E-ELT science and generally require either ‘high multiplex' or 'high definition' observations to best exploit the excellent sensitivity and spatial performance of the telescope. We highlight some of the science studies that are now being used in trade-off studies to inform the capabilities of MOSAIC and its technical design.
The goal of the COMPASS project was to bring together the efforts of the actors from the French AO community (PHASE partnership), with the participation of the Maison de la Simulation, around the collaborative development of a numerical platform for AO, optimized and based on the use of graphics processing units (GPU). This platform allows today to lead the design studies of AO modules addressing all of the first generation instrumentation of the E-ELT. In this paper, we provide a status update of the platform and the long term maintenance and development plan.
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.
C. Evans, M. Puech, B. Barbuy, P. Bonifacio, J.-G. Cuby, E. Guenther, F. Hammer, P. Jagourel, L. Kaper, S. Morris, J. Afonso, P. Amram, H. Aussel, A. Basden, N. Bastian, G. Battaglia, B. Biller, N. Bouché, E. Caffau, S. Charlot, Y. Clénet, F. Combes, C. Conselice, T. Contini, G. Dalton, B. Davies, K. Disseau, J. Dunlop, F. Fiore, H. Flores, T. Fusco, D. Gadotti, A. Gallazzi, E. Giallongo, T. Gonçalves, D. Gratadour, V. Hill, M. Huertas-Company, R. Ibata, S. Larsen, O. Le Fèvre, B. Lemasle, C. Maraston, S. Mei, Y. Mellier, G. Östlin, T. Paumard, R. Pello, L. Pentericci, P. Petitjean, M. Roth, D. Rouan, D. Schaerer, E. Telles, S. Trager, N. Welikala, S. Zibetti, B. Ziegler
Over the past 18 months we have revisited the science requirements for a multi-object spectrograph (MOS) for the
European Extremely Large Telescope (E-ELT). These efforts span the full range of E-ELT science and include input
from a broad cross-section of astronomers across the ESO partner countries. In this contribution we summarise the key
cases relating to studies of high-redshift galaxies, galaxy evolution, and stellar populations, with a more expansive
presentation of a new case relating to detection of exoplanets in stellar clusters. A general requirement is the need for
two observational modes to best exploit the large (≥40 arcmin2) patrol field of the E-ELT. The first mode (‘high
multiplex’) requires integrated-light (or coarsely resolved) optical/near-IR spectroscopy of >100 objects simultaneously.
The second (‘high definition’), enabled by wide-field adaptive optics, requires spatially-resolved, near-IR of >10
objects/sub-fields. Within the context of the conceptual study for an ELT-MOS called MOSAIC, we summarise the toplevel
requirements from each case and introduce the next steps in the design process.
The Universe is comprised of hundreds of billions of galaxies, each populated by hundreds of billions of stars. Astrophysics aims to understand the complexity of this almost incommensurable number of stars, stellar clusters and galaxies, including their spatial distribution, formation, and current interactions with the interstellar and intergalactic media. A considerable fraction of astrophysical discoveries require large statistical samples, which can only be addressed with multi-object spectrographs (MOS). Here we introduce the MOSAIC study of an optical/near-infrared MOS for the European Extremely Large Telescope (E-ELT), which has capabilities specified by science cases ranging from stellar physics and exoplanet studies to galaxy evolution and cosmology. Recent studies of critical technical issues such as sky-background subtraction and multi-object adaptive optics (MOAO) have demonstrated that such a MOS is feasible with current technology and techniques. In the 2020s the E-ELT will become the world’s largest optical/IR telescope, and we argue that it has to be equipped as soon as possible with a MOS. MOSAIC will provide a vast discovery space, enabled by a multiplex of ∼ 200 and spectral resolving powers of R = 5 000 and 20 000. MOSAIC will also offer the unique capability of 10-to-20 ‘high-definition’ (MOAO) integral-field units, optimised to investigate the physics of the sources of reionisation, providing the most efficient follow-up of observations with the James Webb Space Telescope (JWST). The combination of these modes will enable the study of the mass-assembly history of galaxies over cosmic time, including high-redshift dwarf galaxies and studies of the distribution of the intergalactic medium. It will also provide spectroscopy of resolved stars in external galaxies at unprecedented distances, from the outskirts of the Local Group for main-sequence stars, to a significant volume of the local Universe, including nearby galaxy clusters, for luminous red supergiants.
To understand the physical processes taking place in galaxy formation and evolution, the ability to obtain resolved spectroscopy and images across the objects is a must. Distant galaxies are marginally resolved in seeing-limited conditions and Adaptive Optics (AO) is required. Most of the current extra-galactic AO studies are however constrained by the number of targets available to AO correction (the so-called sky coverage), and the need for statistics, that requires observing many objects across the largest possible field. These constraints are now significantly reduced by the new Wide Field AO systems, like GeMS, the Gemini MCAO system. In this paper, we try to understand the impact of the AO-PSF on the galaxies' morphology analysis accuracy. For this, we use realistic simulated data in order to assess the morphological parameters, taking into account partial PSF knowledge. This allows us to define the critical parameters of the MCAO PSF affecting the analysis accuracy.
MOONS is a new Multi-Object Optical and Near-infrared Spectrograph selected by ESO as a third generation
instrument for the Very Large Telescope (VLT). The grasp of the large collecting area offered by the VLT (8.2m
diameter), combined with the large multiplex and wavelength coverage (optical to near-IR: 0.8μm - 1.8μm) of MOONS
will provide the European astronomical community with a powerful, unique instrument able to pioneer a wide range of
Galactic, Extragalactic and Cosmological studies and provide crucial follow-up for major facilities such as Gaia,
VISTA, Euclid and LSST. MOONS has the observational power needed to unveil galaxy formation and evolution over
the entire history of the Universe, from stars in our Milky Way, through the redshift desert, and up to the epoch of very
first galaxies and re-ionization of the Universe at redshift z>8-9, just few million years after the Big Bang. On a
timescale of 5 years of observations, MOONS will provide high quality spectra for >3M stars in our Galaxy and the
local group, and for 1-2M galaxies at z>1 (SDSS-like survey), promising to revolutionise our understanding of the
Universe.
The baseline design consists of ~1000 fibers deployable over a field of view of ~500 square arcmin, the largest patrol
field offered by the Nasmyth focus at the VLT. The total wavelength coverage is 0.8μm-1.8μm and two resolution
modes: medium resolution and high resolution. In the medium resolution mode (R~4,000-6,000) the entire wavelength
range 0.8μm-1.8μm is observed simultaneously, while the high resolution mode covers simultaneously three selected
spectral regions: one around the CaII triplet (at R~8,000) to measure radial velocities, and two regions at R~20,000 one
in the J-band and one in the H-band, for detailed measurements of chemical abundances.
Multichannel Subtractive Double Pass (MSDP) spectrographs have been widely used in solar spectroscopy because of
their ability to provide an excellent compromise between field of view and spatial and spectral resolutions. Compared
with other types of spectrographs, MSDP can deliver simultaneous monochromatic images at higher spatial and spectral
resolutions without any time-scanning requirement (as with Fabry-Perot spectrographs), and with limited loss of flux.
These performances are obtained thanks to a double pass through the dispersive element. Recent advances with VPH
(Volume phase holographic) Grisms as well as with image slicers now make MSDP potentially sensitive to much smaller
fluxes. We present S4EI (Spectral Sampling with Slicer for Stellar and Extragalactical Instrumentation), which is a new
concept for extending MSDP to night-time astronomy. It is based on new generation reflecting plane image slicers
working with large apertures specific to night-time telescopes. The resulting design could be potentially very attractive
and innovative for different domains of astronomy, e.g., the simultaneous spatial mapping of accurately flux-calibrated
emission lines between OH sky lines in extragalactic astronomy or the simultaneous imaging of stars, exoplanets and
interstellar medium. We present different possible MSDP/S4EI configurations for these science cases and expected
performances on telescopes such as the VLT.
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.
KEYWORDS: Fringe analysis, Galactic astronomy, Spectrographs, Data archive systems, Light scattering, Signal to noise ratio, Visualization, Data modeling, Image quality, Large telescopes
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.
MOONS is a new conceptual design for a Multi-Object Optical and Near-infrared Spectrograph for the Very Large
Telescope (VLT), selected by ESO for a Phase A study. The baseline design consists of ~1000 fibers deployable over a
field of view of ~500 square arcmin, the largest patrol field offered by the Nasmyth focus at the VLT. The total
wavelength coverage is 0.8μm-1.8μm and two resolution modes: medium resolution and high resolution. In the medium
resolution mode (R~4,000-6,000) the entire wavelength range 0.8μm-1.8μm is observed simultaneously, while the high
resolution mode covers simultaneously three selected spectral regions: one around the CaII triplet (at R~8,000) to
measure radial velocities, and two regions at R~20,000 one in the J-band and one in the H-band, for detailed
measurements of chemical abundances.
The grasp of the 8.2m Very Large Telescope (VLT) combined with the large multiplex and wavelength coverage of
MOONS – extending into the near-IR – will provide the observational power necessary to study galaxy formation and
evolution over the entire history of the Universe, from our Milky Way, through the redshift desert and up to the epoch
of re-ionization at z<8-9. At the same time, the high spectral resolution mode will allow astronomers to study chemical
abundances of stars in our Galaxy, in particular in the highly obscured regions of the Bulge, and provide the necessary
follow-up of the Gaia mission. Such characteristics and versatility make MOONS the long-awaited workhorse near-IR
MOS for the VLT, which will perfectly complement optical spectroscopy performed by FLAMES and VIMOS.
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 E-ELT.
The OPTIMOS-EVE concept provides optical to near-infrared (370-1700 nm) spectroscopy, with three spectral
resolution (5000, 15000 and 30000), with high simultaneous multiplex (at least 200). The optical fibre links are
distributed in four kinds of bundles: several hundreds of mono-object systems with three types of bundles, fibre size
being used to adapt spectral resolution and 30 deployable medium IFUs (about 2"x3"). We are optimising the design of
deployable IFUs to warrant sky subtraction for the faintest extragalactic sources.
This paper gives the design and results of the prototype for the high resolution mode and the preliminary design of a
medium IFU developed in collaboration between the GEPI and the LNA.
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.
EAGLE is the multi-object spatially-resolved near-IR spectrograph instrument concept for the E-ELT, relying
on a distributed Adaptive Optics, so-called Multi Object Adaptive Optics. This paper presents the results of
a phase A study. Using 84×84 actuator deformable mirrors, the performed analysis demonstrates that 6 laser
guide stars (on an outer ring of 7.2' diameter) and up to 5 natural guide stars of magnitude R < 17, picked-up in
a 7.3' diameter patrol field of view, allow us to obtain an overall performance in terms of Ensquared Energy of
35% in a 75×75mas2 resolution element at H band whatever the target direction in the centred 5' science field
for median seeing conditions. In terms of sky coverage, the probability to find the 5 natural guide stars is close
to 90% at galactic latitudes |b| ~ 60 deg. Several MOAO demonstration activities are also on-going.
In the frame of the EAGLE phase A study, we have developed a scientific simulator which has been used to constrain the instrument high level specifications. This simulator was coupled to a web interface to allow an easier access by the EAGLE science team, and run specific simulations covering the EAGLE scientific objectives. We give a functional description of this simulator, and illustrate how it was used in practice to derive a specification on the Ensquared Energy of EAGLE. Given the success of the EAGLE simulator, we developed other telescope/instrument simulators, including a general image/datacube simulator which is now freely accessible on the web.
We present a new method to subtract sky light from faint object observations with fiber-fed spectrographs. The
algorithm has been developed in the framework of the phase A of OPTIMOS-EVE, an optical-to-IR multi-object
spectrograph for the future european extremely large telescope (E-ELT). The new technique overcomes the
apparent limitation of fiber-fed instrument to recover with high accuracy the sky contribution. The algorithm
is based on the reconstruction of the spatial fluctuations of the sky background (both continuum and emission)
and allows us to subtract the sky background contribution in an FoV of 7 × 7 arcmin2 with an accuracy of 1%
in the mono-fibers mode, and 0.3-0.4% for integral-field-unit observations.
EAGLE is a Phase A study of a multi-IFU, near-IR spectrometer for the European Extremely Large Telescope (E-ELT).
The design employs wide-field adaptive optics to deliver excellent image quality across a large (38.5 arcmin2) field.
When combined with the light grasp of the E-ELT, EAGLE will be a unique and efficient facility for spatially-resolved,
spectroscopic surveys of high-redshift galaxies and resolved stellar populations. Following a brief overview of the
science case, here we summarise the functional and performance requirements that flow-down from it, provide
illustrative performances from simulated observations, and highlight the strong synergies with the James Webb Space
Telescope (JWST) and the Atacama Large Millimeter Array (ALMA).
OPTIMOS-EVE (OPTical Infrared Multi Object Spectrograph - Extreme Visual Explorer) is the fibre fed multi object
spectrograph proposed for the European Extremely Large Telescope (E-ELT), planned to be operational in 2018 at Cerro
Armazones (Chile). It is designed to provide a spectral resolution of 6000, 18000 or 30000, at wavelengths from 370 nm
to 1.7 μm, combined with a high multiplex (>200) and a large spectral coverage. Additionally medium and large IFUs
are available. The system consists of three main modules: a fibre positioning system, fibres and a spectrograph.
The recently finished OPTIMOS-EVE Phase-A study, carried out within the framework of the ESO E-ELT
instrumentation studies, has been performed by an international consortium consisting of institutes from France,
Netherlands, United Kingdom and Italy. All three main science themes of the E-ELT are covered by this instrument:
Planets and Stars; Stars and Galaxies; Galaxies and Cosmology.
This paper gives an overview of the OPTIMOS-EVE project, describing the science cases, top level requirements, the
overall technical concept and the project management approach. It includes a description of the consortium, highlights of
the science drivers and resulting science requirements, an overview of the instrument design and telescope interfaces, the
operational concept, expected performance, work breakdown and management structure for the construction of the
instrument, cost and schedule.
EAGLE is an instrument for the European Extremely Large Telescope (E-ELT). EAGLE will be installed at the Gravity
Invariant Focal Station of the E-ELT, covering a field of view of 50 square arcminutes. Its main scientific drivers are the
physics and evolution of high-redshift galaxies, the detection and characterization of first-light objects and the physics of
galaxy evolution from stellar archaeology. These key science programs, generic to all ELT projects and highly
complementary to JWST, require 3D spectroscopy on a limited (~20) number of targets, full near IR coverage up to 2.4
micron and an image quality significantly sharper than the atmospheric seeing. The EAGLE design achieves these
requirements with innovative, yet simple, solutions and technologies already available or under the final stages of
development. EAGLE relies on Multi-Object Adaptive Optics (MOAO) which is being demonstrated in the laboratory
and on sky. This paper provides a summary of the phase A study instrument design.
We present an end-to-end simulator for 3D spectroscopy, which can be used to specify MOAO-fed integral field
spectrographs dedicated to ELTs. This simulator re-scales either local data or outputs of hydro-dynamical simulations to
model distant galaxies. We present simulations of 3D observations in the H-band, for a rotating disk and a major merger
at z=4, and a large range of stellar-mass. We use these simulations to explore the parameter space, focusing on the
impact of the telescope diameter, total integration time, spectral resolution, and IFU pixel scale. The size of the telescope
diameter has little influence on the spatial resolution of 3D observations but largely influences the achieved SNR. The
choice of the IFU pixel scale is driven by the optimal "scale-coupling", i.e., the relation between the spatial resolution of
3D observations and the physical size of the features for which one needs to recover the kinematics using this IFU, and
the SNR achieved with this spatial scale. To recover the dynamical state of distant emission line galaxies, one of the
main goal of such future instruments, one only needs to recover their large-scale motions, which in turn requires only
relatively coarse IFU pixel scales (50-75 mas) and moderate spectral resolution (R=5000).
E-ELT will provide a unique opportunity to observe the early universe since its large collecting area will allow detecting
faint objects at high redshifts. Primordial galaxies are a key topic for cosmology and for understanding the behaviour of
the galaxies in the universe. To achieve these observations, future instruments for the E-ELT will have to provide high
sensitivity over a wide range of wavelengths from 1 μm up to 2.5 μm - the upper limit being imposed by the redshift
which shifts the OII and Hα lines.
For the EAGLE instrument mainly devoted to such observations, we have studied the opto-thermal behaviour of the
complete system (TAS - Target Acquisition System - and the spectrograph) to estimate the thermal emission of the
optical and the mechanical parts which become a major contributor to the background above 2.2 μm. The nominal
operating temperature is a key parameter we must define precisely to both reduce the thermal background and optimise
the cooling system in terms of cost and complexity. The results of the simulations show that the TAS and the
spectrograph contribute to the thermal background at a similar level and what the optimal temperature should be. We
then discuss how such an 'optimal design' might be implemented in practice.
X-shooter is a new high-efficiency integral field spectrograph mainly dedicated to the spectroscopic follow up of the gamma ray bursts. X-shooter will operate at the Cassegrain focus of the VLT with an intermediate spectral resolution of ~5000, and will provide a very wide simultaneous spectral coverage, ranging from 320 to 2500 nm. The instrument consists in a central structure which supports three prism cross-dispersed echelle spectrographs respectively optimized for the UV-blue, Visible and Near-IR wavelength ranges.
X-shooter will offer an image slicer based Integral Field Unit (IFU) designed to analyse a 1.8"x4" input field into 3 slices of 0.6"x4"and to align then on a 12" long slit. The principle of the IFU is that the central slice does not include any dioptre, the light is directly transmitted to the spectrographs. Only the two lateral sliced fields are reflected toward the two pairs of spherical mirrors and re-aligned at both ends of the previous slice in order to form the exit slit. We present here the IFU design developed at the Observatoire de Paris.
We report on the science case high level specifications for a wide field spectrograph instrument for an Extremely Large
Telescope (ELT) and present possible concepts. Preliminary designs are presented which resort to different instrument
concepts: monolithic integral field (IFU), multi-IFU, and a smart tunable filter. This work is part of the activities performed
in the work package 'Instrumentation' of the 'ELT Design Study', a programme supported by the European Community,
Framework Programme 6.
In the last few years, new Adaptive Optics [AO] techniques have emerged to answer new astronomical challenges:
Ground-Layer AO [GLAO] and Multi-Conjugate AO [MCAO] to access a wider Field of View [FoV], Multi-Object
AO [MOAO] for the simultaneous observation of several faint galaxies, eXtreme AO [XAO] for the detection
of faint companions. In this paper, we focus our study to one of these applications : high red-shift galaxy
observations using MOAO techniques in the framework of Extremely Large Telescopes [ELTs]. We present the
high-level specifications of a dedicated instrument. We choose to describe the scientific requirements with the
following criteria : 40% of Ensquared Energy [EE] in H band (1.65μm) and in an aperture size from 25 to 150 mas.
Considering these specifications we investigate different AO solutions thanks to Fourier based simulations. Sky
Coverage [SC] is computed for Natural and Laser Guide Stars [NGS, LGS] systems. We show that specifications
are met for NGS-based systems at the cost of an extremely low SC. For the LGS approach, the option of low
order correction with a faint NGS is discussed. We demonstrate that, this last solution allows the scientific
requirements to be met together with a quasi full SC.
FALCON is an original concept for next generation instrumentation at ESO VLT or at future ELTs. It is a multi-objects integral field spectrograph with multiple integral field units (IFU) performing adaptive optics correction in order to reach spatial and spectral resolution ideally suited for distant galaxy studies. The resolutions required for the VLT are typically 0.15 - 0.25 arcsec and R>=5000 in the 0.8-1.8 μm wavelength range. The studied galaxies are very faint objects that cannot be directly used to perform wavefront sensing. Thus, we use at least three Wave-Front Sensors (WFS) per IFU to sense the wavefront of stars located around the galaxy, and the on-axis wavefront from the galaxy will be deduced from the off-axis measurements by atmospheric tomography, and then corrected thanks to an adaptive optics (AO) system within each IFU. Since the WFS is ideally located directly in the focal plane of the telescope, this implies to develop miniaturized devices for the wavefront sensing. Our approach is based on a Shack Hartmann principle and - instead of using a bulky detector behind - we plan to use a miniaturized system including fibers able to transport the light from the focal plane of the microlens array towards a place where the bulk issue is less critical. We draw up the main specifications of this miniaturized system and we present the characteristics of elements manufactured by using new microlithography techniques.
FALCON is an original concept for a next generation instrument which could be used on the ESO Very Large Telescope (VLT) and on the future Extremely Large Telescopes (ELT). It is a multi-objects integral field spectrograph with multiple small integral field units (IFUs). Each of them integrates a tiny adaptive optics system coupled with atmospheric tomography to solve the sky coverage problem. This therefore allows to reach spatial (0.15 - 0.25 arcsec) and spectral (R>=5000) resolutions suitable for distant galaxy studies in the 0.8-1.8 μm wavelength range. In the FALCON concept, the adaptive optics correction is only applied on small and discrete areas selected within a large field. This approach implies to develop miniaturized devices for wavefront correction such as deformable mirrors (DM) and wavefront sensors (WFS). We draw up here the main high level specifications for this instrument, that we derive in a first set of opto-mechanical DM requirements including the state of the art of DM technologies.
FALCON (a Fiber spectrograph with Adaptive optics on Large fields to correct at Optical and Near-infrared) is an original concept for a next generation instrumentation at ESO VLT or at future ELTs. It is a multi-objects integral field spectrograph with multiple integral field small units, each being coupled with atmospheric tomography in order to reach spatial and spectral resolution ideally suited for distant galaxy studies: typically 0.15 - 0.25 arcsec and R>=5000 in the 0.8-1.8 μm wavelength range. In the FALCON concept the adaptive optics correction is only applied on small and discrete areas selected on a large field. This approach implies to develop some miniaturized devices for adaptive optics correction and wavefront sensing. We present here some recent technological results.
FALCON is an original concept for a next generation spectrograph at ESO VLT or at future ELTs. It is a spectrograph including multiple small integral field units (IFUs) which can be deployed within a large field of view such as that of VLT/GIRAFFE. In FALCON, each IFU features an adaptive optics correction using off-axis natural reference stars in order to combine, in the 0.8 - 1.8 μm wavelength range, spatial and spectral resolutions (0.1 - 0.15 arcsec and R = 1000 +/- 5000). These conditions are ideally suited for distant galaxy studies, which should be done within fields of view larger than the galaxy clustering scales (4 - 9 Mpc), i.e. foV > 100 arcmin. Instead of compensating the whole field, the adaptive correction will be performed locally on each IFU. This implies to use small miniaturized devices both for adaptive optics correction and wavefront sensing. Applications to high latitude fields imply to use atmospheric tomography because the stars required for wavefront sensing will be in most of the cases far outside the isoplanatic patch.
We present FALCON, a concept of new generation multi-objects integral field spectrograph with adaptive optics for the ESO VLT. The goal of FALCON is to combine high angular resolution (0.15 - 0.25 arcsec) and high spectral resolution (R≥5000) in the 0.8-1.8 μm wavelength range across the Nasmyth field (25 arcmin). Instead of compensating the whole field, the correction will be performed locally on each scientific object. This implies to use small miniaturized devices for adaptive optics correction and wavefront sensing. The main scientific objective of FALCON will be extragalactic astronomy. It will therefore have to use atmospheric tomography because the stars required for wavefront sensing will be in most of the cases far outside the isoplanatic patch. We show in this paper that applying adaptive optics correction will provide an important increase in signal to noise ratio, especially for distant galaxies at high redshift.
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