MOSAIC is a mixed-mode multiple object spectrograph planned for the ELT that uses a tiled focal plane to support a variety of observing modes. The MOSAIC AO system uses 4 LGS WFS and up to 4 NGS WFS positioned anywhere within the full 10 arcminute ELT field of view to control either the ELT M4/5 alone for GLAO operation feeding up to 200 targets in the focal plane, or M4/5 in conjunction with 10 open-loop DMs for MOAO correction. In this paper we present the overall design and performance of the MOSAIC GLAO and MOAO systems.
Assembly, Integration, Test and Validation (AIT/V) phases for AO instruments, in laboratory as in the telescope, represent numerous technical challenges. The Laboratoire d’Astrophysique de Marseille (LAM) is in charge of the AIT/V preparation and planning for the MOSAIC (ELT-MOS) instrument, from identification of needs, challenges, risks, to defining the optimal AIT strategy for this highly modular and serialized instrument. In this paper, we present the status of this study and describe several AIT/V scenarios as well as a planning for AIT phases in Europe and in Chile. We also show our capabilities, experience and expertise to lead the instrument MOSAIC AIT/V activities.
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 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: 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.
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.
MOSAIC is the proposed multiple-object spectrograph for the E-ELT that will utilise the widest possible field of view provided by the telescope. In terms of adaptive optics, there are two distinct operating modes required to meet the top-level science requirements. The MOSAIC High Multiplex Mode (HMM) requires either seeing-limited or GLAO correction within a 0.6 (NIR) and 0.9 (VIS) arcsecond sub-fields over the widest possible field for a few hundred objects. To achieve seeing limited operation whilst maintaining the maximum unvignetted field of view for scientific observation will require recreating some of the functionality present in the Pre-Focal Station relating to control of the E-ELT active optics. MOSAIC High Definition Mode Control (HDM) requires a 25% Ensquared Energy (EE) within 150mas in the H-band element for approximately 10 targets distributed across the full E-ELT field, implying the use of Multiple Object AO (MOAO). Initial studies have shown that to meet the EE requirements whilst maintaining high-sky coverage will require the combination of wavefront signals from both high-order NGS and LGS to provide a tomographic estimate for the correction to be applied to the open-loop MOAO DMs. In this paper we present the current MOSAIC AO design and provide the first performance estimates for the baseline instrument design. We then report on the various trade-offs that will be investigated throughout the course of the Phase A study, such as the requirement to mix NGS and LGS signals tomographically. Finally, we discuss how these will impact the AO architecture, the MOSAIC design and ultimately the scientific performance of this wide-field workhorse instrument at the E-ELT.
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.
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.
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 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.
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.
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.
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.
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.
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.
OPTIMOS-EVE (OPTical Infrared Multi Object Spectrograph - Extreme Visual Explorer) is the fiber fed multi object
spectrograph proposed for the E-ELT. It is designed to provide a spectral resolution ranging from 5000 to 30.000, at
wavelengths from 0.37 μm to 1.70 μm, combined with a high multiplex (>200) and a large spectral coverage. The
system consists of three main modules: a fiber positioning system, fibers and a spectrograph.
The 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, Italy
and Denmark.
This paper describes the design tradeoff study and the key issues determining the price and performance of the
instrument.
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 five kinds of bundles: several hundreds of mono-object systems with three types of bundles, fibre size
being used to adapt slit with, and thus spectral resolution, 30 deployable medium IFUs (about 2"×3") and one large IFU
(about 6"×12").
This paper gives an overview of the design of each mode and describes the specific developments required to optimise
the performances of the fibre system.
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.
X-shooter is the first second-generation instrument newly commissioned a the VLT. It is a high efficiency single
target intermediate resolution spectrograph covering the range 300 - 2500 nm in a single shot. We summarize
the main characteristics of the instrument and present its performances as measured during commissioning and
the first months of science operations.
We present a project aimed at establishing a set of 12 spectro-photometric standards over a wide wavelength range from
320 to 2500 nm. Currently no such set of standard stars covering the near-IR is available. Our strategy is to extend the
useful range of existing well-established optical flux standards into the near-IR by means of integral field spectroscopy
with SINFONI at the VLT combined with state-of-the-art white dwarf stellar atmospheric models. As a solid reference,
we use two primary HST standard white dwarfs. This ESO "Observatory Programme" has been collecting data since
February 2007. The analysis of the data obtained in the first year of the project shows that a careful selection of the
atmospheric windows used to measure fluxes and the stability of SINFONI make it possible to achieve an accuracy of 3-
6% depending on the wavelength band and stellar magnitude, well within our original goal of 10% accuracy. While this
project was originally tailored to the needs of the wide wavelength range (320-2500 nm) of X-shooter on the VLT, it will
also benefit any other near-IR spectrographs, providing a huge improvement over existing flux calibration methods.
Increasing dimensions of ground based telescopes while implementing Adaptive Optics systems to cancel both structural
deformations and atmospheric effects require very large diameters deformable mirrors (DM) and a high number of
actuators with large strokes. This has led for the future E-ELT to a 2.5 m diameter DM getting about 8000 actuators.
This paper presents a local and a global model of the DM in order to both study its influence function and its dynamical
behavior. In the first part, influence function of the mirror is calculated. Results obtained by an analytical way are
compared to those obtained numerically. In the second part, modal analysis of the mirror is presented. Results are limited
to the first modes. Modal analysis is also only made for the base plate to derive the specific influence of DM's
components on the global dynamic behavior. In the last part, optimization methods are used to help designing a 1 m
prototype of the DM.
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.
X-shooter is a single target spectrograph for the Cassegrain focus of one of the VLT UTs where it will start to operate in
2008. The instrument covers in a single exposure the spectral range from the UV to the K' band. It is designed to
maximize the sensitivity in this spectral range through the splitting in three arms with optimized optics, coatings,
dispersive elements and detectors. It operates at intermediate resolutions (R=4000-14000, depending on wavelength and
slit width) with fixed echelle spectral format (with prism cross-dispersers) in the three arms. The project has completed
the Final Design Review in June 2006. In this status report, the overall concept is summarized and new results on the
dichroics, the active flexure compensation system, the operation modes and the expected performance are given. The
instrument is being built by a Consortium of Institutes from Denmark, France, Italy and the Netherlands in collaboration
with ESO. When in operation, its wide spectral range observing capability will be unique at very large telescopes.
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.
We report on the development of instrument concepts for a European ELT, expanding on studies carried out as part of the ESO OWL concept. A range of instruments were chosen to demonstrate how an ELT could meet or approach the goals generated by the OPTICON science team, and used to push the specifications and requirements of telescope and adaptive optics systems. Preliminary conclusions are presented, along with a plan for further more detailed instrument design and technology developments. This activity is supported by the European Community (Framework Programme 6, ELT Design Study, contract number 011863).
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.
X-shooter is a single target spectrograph for the Cassegrain focus of one of the VLT UTs. It covers in a single exposure the spectral range from the UV to the H band with a possible extension into part of the K band. It is designed to maximize the sensitivity in this spectral range through the splitting in three arms with optimized optics, coatings, dispersive elements and detectors. It operates at intermediate resolutions (R=4000-14000, depending on wavelength and slit width) sufficient to address quantitatively a vast number of astrophysical applications while working in a background-limited S/N regime in the regions of the spectrum free from strong atmospheric emission and absorption lines. The small number of moving functions (and therefore instrument modes) and fixed spectral format make it easy to operate and permit a fast response. A mini-IFU unit (1.8" x 4") can be inserted in the telescope focal plane and is reformatted in a slit of 0.6"x 12" .The instrument includes atmospheric dispersion correctors in the UV and visual arms. The project foresees the development of a fully automatic data reduction package. The name of the instrument has been inspired by its capability to observe in a single shot a source of unknown flux distribution and redshift. The instrument is being built by a Consortium of Institutes from Denmark, France, Italy and the Netherlands in collaboration with ESO. When it operation, its observing capability will be unique at very large telescopes.
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.
In May 2000, the Canada-France-Hawaii (CFHT) Telescope Science Advisory Committee solicited the Canadian, Hawaiian and French communities to propose concepts to replace the present CFH telescope by a larger telescope. Three groups were selected: Carlberg et al. (2001) in Canada, Khun et al. (2001) in Hawaii and Burgarella et al. (2001a) in France. The reports were delivered to CFHT in May 2001 and are now available throughout the CFHT website. One of the main constraints was due to the fact that the new and larger telescope should use as much as possible the existing site and be compliant with the Mauna Kea Science reserve Master Plan (2000). This plan analyses all aspects of the Mauna Kea summit but most of them are related to the facts that the mountain must be considered as a sacred area for indigenous Hawaiian people and that the ecosystem is fragile. But in addition, the plan also tries to account for the fact that the summit of Mauna Kea is a world famous site for astronomy. The points that we can highlight in the context of our project are of two types. Since then, the project evolved and Hawaii is not considered as the one and only site to build an Extremely Large Telescope (ELT). Moreover, the size of the primary mirror, which was strongly dependent on the above constraints, is no more limited to the 16 - 20 m which was our conclusion at this time. Nevertheless, the three points of the resolution are still valid and since then, we have kept on working on the concept by launching differnt follow-up studies that are necessary to start such a project. Of course, the main point is the Science Objectives which drive the main specifications for an ELT. But related technical studies are also mandatory e.g. Adaptive Optics, Building of a primary mirror larger than 30 m in diameter, Image Quality as a function of the segment size and shape.
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.
Considered until recently one of the best telescopes in the world, the Canada-France-Hawaii Telescope (CFHT) is now bypassed by larger telescopes. Aware of this problem, the CFHT Science Advisory Council (SAC) solicited proposals from the CFH community groups to replace the present telescope by a world-class research facility before the end of the decade. A report describing our proposal is available on our web site (www.astrsp-mrs.fr/denis/ngcfht/ngcfht.html). The motivation to design and build a new telescope is often driven by the astronomers need to observe fainter and fainter sources. The basis of the next generation CFHT (NG-CFHT) is therefore to increase the size of the primary mirror to reach fainter and more remote objects in the luminosity functions. But beyond this photon quest , the way we use the photons is also very important. The development of new technologies will permit an optimization of performances and a better image quality thanks to state-of-the-art instruments on state-of-the-art telescopes.
Our team is designing and realizing the fiber links from which two spectrographs will operate at the second unit of the Very Large Telescope. GIRAFFE is an intermediate resolution spectrograph which has access to the entire field of the Nasmyth focus and is equipped with three fiber links producing alternately 132 spectra at the same time, 15 tri- dimensional spectra or 300 spectra for a single object. The last fiber link is intended to provide simultaneously with GIRAFFE, the observation of 8 objects at a higher resolution with UVES. All these observation modes will be available at VLT by the end of 2001. The specific development of the fiber links includes the systematic use of simultaneous calibration. This paper sums up the design of each mode and describes the specific developments required to optimize the performances of the fiber system. A full description of GIRAFFE, of its fiber link and of the related scientific programs is available at http://giraobs.obspm.fr.
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