In this paper, we describe the wide-field spectroscopic survey telescope (WST) project. WST is a 12-metre wide-field spectroscopic survey telescope with simultaneous operation of a large field-of-view (3 sq. degree), high-multiplex (20,000) multi-object spectrograph (MOS), with both a low and high-resolution modes, and a giant 3×3 arcmin2 integral field spectrograph (IFS). In scientific capability, these specifications place WST far ahead of existing and planned facilities. In only 5 years of operation, the MOS would target 250 million galaxies and 25 million stars at low spectral resolution, plus 2 million stars at high resolution. Without need for pre-imaged targets, the IFS would deliver 4 billion spectra offering many serendipitous discoveries. Given the current investment in deep imaging surveys and noting the diagnostic power of spectroscopy, WST will fill a crucial gap in astronomical capability and work in synergy with future ground and space-based facilities. We show how it can address outstanding scientific questions in the areas of cosmology; galaxy assembly, evolution, and enrichment, including our own Milky Way; the origin of stars and planets; and time domain and multi-messenger astrophysics. WST’s uniquely rich dataset may yield unforeseen discoveries in many of these areas. The telescope and instruments are designed as an integrated system and will mostly use existing technology, with the aim to minimise the carbon footprint and environmental impact. We will propose WST as the next European Southern Observatory (ESO) project after completion of the 39-metre ELT.
BlueMUSE is a blue-optimised, medium spectral resolution, panoramic integral field spectrograph based on the MUSE concept and proposed for the Very Large Telescope.
With an optimised transmission down to 350 nm, a larger FoV (1.4 × 1.4 arcmin2) and a higher spectral resolution (λ/Δλ ~ 4000) compared to MUSE, BlueMUSE will open up a new range of galactic and extragalactic science cases allowed by its specific capabilities in the 350-580nm range, beyond those possible with MUSE.
In this paper, we present the optomechanical architecture and design of BlueMUSE at pre-phase A level, with a particular attention to some original aspects such as the use of curved detectors.
BlueMUSE (Blue Multi Unit Spectroscopic Explorer) is a blue-optimised, medium spectral resolution, panoramic integral field spectrograph proposed for the Very Large Telescope (VLT) and based on the MUSE concept. BlueMUSE will open up a new range of galactic and extragalactic science cases allowed by its specific capabilities in the 350 - 580 nm range: an optimised end-to-end transmission down to 350 nm, a larger FoV (up to 1.4 x 1.4 arcmin²) sampled at 0.3 arcsec, and a higher spectral resolution (λ/Δλ ~ 3500) compared to MUSE. To our knowledge, achieving such capabilities with a comparable mechanical footprint and an identical detector format (4k x 4k, 15 µm CCD) would not be possible with a conventional spectrograph design.
In this paper, we present the optomechanical architecture and design of BlueMUSE at pre-phase A level, with a particular attention to some original aspects such as the use of curved detectors.
HARMONI is the E-ELT’s first light visible and near-infrared integral field spectrograph. It will provide four different spatial scales, ranging from coarse spaxels of 60 × 30 mas best suited for seeing limited observations, to 4 mas spaxels that Nyquist sample the diffraction limited point spread function of the E-ELT at near-infrared wavelengths. Each spaxel scale may be combined with eleven spectral settings, that provide a range of spectral resolving powers (R ~3500, 7500 and 20000) and instantaneous wavelength coverage spanning the 0.5 – 2.4 μm wavelength range of the instrument. In autumn 2015, the HARMONI project started the Preliminary Design Phase, following signature of the contract to design, build, test and commission the instrument, signed between the European Southern Observatory and the UK Science and Technology Facilities Council. Crucially, the contract also includes the preliminary design of the HARMONI Laser Tomographic Adaptive Optics system. The instrument’s technical specifications were finalized in the period leading up to contract signature. In this paper, we report on the first activity carried out during preliminary design, defining the baseline architecture for the system, and the trade-off studies leading up to the choice of baseline.
MUSE (Multi Unit Spectroscopic Explorer) is a second generation instrument built for ESO (European Southern
Observatory). The MUSE project is supported by a European consortium of 7 institutes.
After the finalisation of its integration in Europe, the MUSE instrument has been partially dismounted and shipped to
the VLT (Very Large Telescope) in Chile. From October 2013 till February 2014, it has then been reassembled, tested
and finally installed on the telescope its final home. From there it collects its first photons coming from the outer limit
of the visible universe.
This critical moment when the instrument finally meets its destiny is the opportunity to look at the overall outcome of
the project and the final performance of the instrument on the sky. The instrument which we dreamt of has become
reality. Are the dreamt performances there as well?
These final instrumental performances are the result of a step by step process of design, manufacturing, assembly, test
and integration. Now is also time to review the path opened by the MUSE project. What challenges were faced during
those last steps, what strategy, what choices did pay off? What did not?
HARMONI is a visible and near-infrared (0.47 to 2.45 μm) integral field spectrometer, providing the E-ELT's core
spectroscopic capability, over a range of resolving powers from R (≡λ/Δλ)~500 to R~20000. The instrument provides simultaneous spectra of ~32000 spaxels at visible and near-IR wavelengths, arranged in a √2:1 aspect ratio contiguous field. HARMONI is conceived as a workhorse instrument, addressing many of the E-ELT’s key science cases, and will
exploit the E-ELT's scientific potential in its early years, starting at first light. HARMONI provides a range of spatial
pixel (spaxel) scales and spectral resolving powers, which permit the user to optimally configure the instrument for a
wide range of science programs; from ultra-sensitive to diffraction limited, spatially resolved, physical (via morphology),
chemical (via abundances and line ratios) and kinematic (via line-of-sight velocities) studies of astrophysical sources.
Recently, the HARMONI design has undergone substantial changes due to significant modifications to the interface with
the telescope and the architecture of the E-ELT Nasmyth platform. We present an overview of the capabilities of
HARMONI, and of its design from a functional and performance viewpoint.
MUSE Instrumentation Software is the software devoted to the control of the Multi-Unit Spectroscopic Explorer
(MUSE), a second-generation VLT panoramic integral-field spectrograph instrument, installed at Paranal in January
2014. It includes an advanced and user-friendly GUI to display the raw data of the 24 detectors, as well as the on-line
reconstructed images of the field of view allowing users to assess the quality of the data in quasi-real
time. Furthermore, it implements the slow guiding system used to remove effects of possible differential drifts between
the telescope guide probe and the instrument, and reach high image stability (<0.03 arcsec RMS stability).
In this paper we report about the software design and describe the developed tools that efficiently support astronomers
while operating this complex instrument at the telescope.
The 4MOST[1] instrument is a concept for a wide-field, fibre-fed high multiplex spectroscopic instrument facility on the
ESO VISTA telescope designed to perform a massive (initially >25x106 spectra in 5 years) combined all-sky public
survey. The main science drivers are: Gaia follow up of chemo-dynamical structure of the Milky Way, stellar radial
velocities, parameters and abundances, chemical tagging; eROSITA follow up of cosmology with x-ray clusters of
galaxies, X-ray AGN/galaxy evolution to z~5, Galactic X-ray sources and resolving the Galactic edge;
Euclid/LSST/SKA and other survey follow up of Dark Energy, Galaxy evolution and transients. The surveys will be
undertaken simultaneously requiring: highly advanced targeting and scheduling software, also comprehensive data
reduction and analysis tools to produce high-level data products. The instrument will allow simultaneous observations of
~1600 targets at R~5,000 from 390-900nm and ~800 targets at R<18,000 in three channels between ~395-675nm
(channel bandwidth: 45nm blue, 57nm green and 69nm red) over a hexagonal field of view of ~ 4.1 degrees. The initial
5-year 4MOST survey is currently expect to start in 2020. We provide and overview of the 4MOST systems: optomechanical,
control, data management and operations concepts; and initial performance estimates.
4MOST is a wide-field, high-multiplex spectroscopic survey facility under development for the VISTA telescope of the European Southern Observatory (ESO). Its main science drivers are in the fields of galactic archeology, high-energy physics, galaxy evolution and cosmology. 4MOST will in particular provide the spectroscopic complements to the large
area surveys coming from space missions like Gaia, eROSITA, Euclid, and PLATO and from ground-based facilities like VISTA, VST, DES, LSST and SKA. The 4MOST baseline concept features a 2.5 degree diameter field-of-view with ~2400 fibres in the focal surface that are configured by a fibre positioner based on the tilting spine principle. The fibres feed two types of spectrographs; ~1600 fibres go to two spectrographs with resolution R<5000 (λ~390-930 nm) and
~800 fibres to a spectrograph with R>18,000 (λ~392-437 nm and 515-572 nm and 605-675 nm). Both types of spectrographs are fixed-configuration, three-channel spectrographs. 4MOST will have an unique operations concept in which 5 year public surveys from both the consortium and the ESO community will be combined and observed in parallel during each exposure, resulting in more than 25 million spectra of targets spread over a large fraction of the
southern sky. The 4MOST Facility Simulator (4FS) was developed to demonstrate the feasibility of this observing
concept. 4MOST has been accepted for implementation by ESO with operations expected to start by the end of 2020.
This paper provides a top-level overview of the 4MOST facility, while other papers in these proceedings provide more
detailed descriptions of the instrument concept[1], the instrument requirements development[2], the systems engineering implementation[3], the instrument model[4], the fibre positioner concepts[5], the fibre feed[6], and the spectrographs[7].
MUSE (Multi Unit Spectroscopic Explorer) is a second generation instrument, built for ESO (European Southern
Observatory) and dedicated to the VLT (Very Large Telescope). This instrument is an innovative integral field
spectrograph (1x1 arcmin2 Field of View), operating in the visible wavelength range, from 465 nm to 930 nm. The
MUSE project is supported by a European consortium of 7 institutes.
After the finalisation of its integration and test in Europe validated by its Preliminary Acceptance in Europe, the MUSE
instrument has been partially dismounted and shipped to the VLT (Very Large Telescope) in Chile. From October 2013
till February 2014, it has then been reassembled, tested and finally installed on the telescope its final home. From there
it will collect its first photons coming from the outer limit of the visible universe.
To come to this achievement, many tasks had to be completed and challenges overcome. These last steps in the project
life have certainly been ones of the most critical. Critical in terms of risk, of working conditions, of operational
constrains, of schedule and finally critical in terms of outcome: The first light and the final performances of the
instrument on the sky.
The Multi Unit Spectroscopic Explorer (MUSE) is a second-generation VLT panoramic integral-field spectrograph. The instrument has been designed to take advantage of the VLT ground layer adaptive optics ESO facility using four laser guide stars. MUSE couples the discovery potential of a large imaging device to the measuring capabilities of a high-quality spectrograph, while taking advantage of the increased spatial resolution provided by adaptive optics. The MUSE hardware is composed of 24 identical modules, each one consisting of an advanced slicer, a spectrograph and a (4k)² detector. A series of fore-optics and splitting and relay optics is in charge of derotating and partitioning the square field of view into 24 sub-fields. With its almost 7 tons of opto-mechanics, MUSE is one of the biggest integral field unit ever built. After a successful preliminary acceptance in Europe in fall 2013, MUSE has been dismounted, shipped to Chile and re-integrated in the Paranal new integration hall and finally installed on the Nasmyth platform of UT4 late January this year. During the 2 commissioning runs, hundreds of millions of spectra have been obtained in order to validate the instrument and measured its achieved performance. To demonstrate its power, a number of show-case and spectacular observations have also been obtained. Preliminary results demonstrate that MUSE is likely to become a new reference in the field of integral field spectroscopy thanks to its large field of view, very high throughput, excellent image quality, good spectral resolution, wide simultaneous spectral range and state-of-the art control and data reduction software. I will review this success story, from the call of idea to the deployment on the VLT, including the latest performances and showcase observations.
The Centre de Recherche Astrophysique de Lyon (CRAL) has recently developed two instrument simulators
for spectrographic instruments. They are based on Fourier optics, and model the whole chain of acquisition,
taking into account both optical aberrations and diffraction effects, by propagating a wavefront through the
instrument, according to the Fourier optics concept. One simulates the NIRSpec instrument, a near-infrared
multi-object spectrograph for the future James Webb Space Telescope (JWST). The other one models the
Multi Unit Spectroscopic Explorer (MUSE) instrument, a second-generation integral-field spectrograph for the
Very Large Telescope (VLT). The two simulators have been developed in different contexts (subcontracted
versus developed internally), and for very different instruments (space-based versus ground-based), which
strengthen the CRAL experience. This paper describes the lessons learned while developing these simulators:
development methods, phasing with the project, points to focus on, getting data, interacting with scientists
and users, etc.
MUSE (Multi Unit Spectroscopic Explorer) is a second generation instrument built for ESO (European Southern
Observatory) to be installed in Chile on the VLT (Very Large Telescope). The MUSE project is supported by a
European consortium of 7 institutes.
After the critical turning point of shifting from the design to the manufacturing phase, the MUSE project has now
completed the realization of its different sub-systems and should finalize its global integration and test in Europe.
To arrive to this point many challenges had to be overcome, many technical difficulties, non compliances or
procurements delays which seemed at the time overwhelming. Now is the time to face the results of our organization, of
our strategy, of our choices. Now is the time to face the reality of the MUSE instrument.
During the design phase a plan was provided by the project management in order to achieve the realization of the
MUSE instrument in specification, time and cost. This critical moment in the project life when the instrument takes
shape and reality is the opportunity to look not only at the outcome but also to see how well we followed the original
plan, what had to be changed or adapted and what should have been.
MUSE (Multi Unit Spectroscopic Explorer) is a second generation VLT panoramic integral field spectrograph developed
for the European Southern Observatory (ESO), operating in the visible wavelength range (0.465-0.93 μm). The MUSE
instrument is currently under integration and the commissioning is expected to start at the beginning of year 2013. The
scientific and technical capabilities of MUSE are described in a series of 19 companion papers. The Fore-Optics (FO),
situated at the entrance of MUSE, is used to de-rotate and provide an anamorphic magnification (x 5 / x 2.5) of the 1 arc
minute square field of view from the F/15.2 VLT Nasmyth focal plane (Wide Field Mode, WFM). Additional optical
elements can be inserted in the optical beam to further increase the magnification by a factor 8 (Narrow Field Mode,
NFM). An atmospheric dispersion corrector is also added in the NFM. Two image stabilization units have been
developed to ensure a stabilization of the field of view (1/20 of a resolved element) for each observation mode.
Environmental values such as temperature and hygrometry are monitored to inform about the observation conditions. All
motorized functions and sensors are remote-controlled from the VLT Software via the CAN bus with CANOpen
protocol. In this paper, we describe the FO optical, mechanical and control/command electronic concept, development
and performance.
MUSE (Multi Unit Spectroscopic Explorer) is a second generation VLT integral field spectrograph (1x1arcmin² Field of View) developed for the European Southern Observatory (ESO), operating in the visible wavelength range (0.465-0.93 μm). A consortium of seven institutes is currently assembling and testing MUSE in the Integration Hall of the
Observatoire de Lyon for the Preliminary Acceptance in Europe, scheduled for 2013.
MUSE is composed of several subsystems which are under the responsibility of each institute. The Fore Optics derotates
and anamorphoses the image at the focal plane. A Splitting and Relay Optics feed the 24 identical Integral Field Units
(IFU), that are mounted within a large monolithic instrument mechanical structure. Each IFU incorporates an image
slicer, a fully refractive spectrograph with VPH-grating and a detector system connected to a global vacuum and
cryogenic system. During 2011, all MUSE subsystems were integrated, aligned and tested independently in each
institute. After validations, the systems were shipped to the P.I. institute at Lyon and were assembled in the Integration
Hall
This paper describes the end-to-end optical alignment procedure of the MUSE instrument. The design strategy, mixing
an optical alignment by manufacturing (plug and play approach) and few adjustments on key components, is presented.
We depict the alignment method for identifying the optical axis using several references located in pupil and image
planes. All tools required to perform the global alignment between each subsystem are described. The success of this
alignment approach is demonstrated by the good results for the MUSE image quality.
MUSE commissioning at the VLT (Very Large Telescope) is planned for 2013.
MUSE, the Multi Unit Spectroscopic Explorer,1 is an integral-field spectrograph under construction for the ESO VLT to
see first light in 2013. It can record spectra of a 1′x1′ field on the sky at a sampling of 0″.2x0″.2, over a wavelength range
from 4650 to 9300Å.
The data reduction for this instrument is the process which converts raw data from the 24 CCDs into a combined
datacube (with two spatial and one wavelength axis) which is corrected for instrumental and atmospheric effects. Since
the instrument consists of many subunits (24 integral-field units, each slicing the light into 48 parts, i. e. 1152 regions with
a total of almost 90000 spectra per exposure), this task requires many steps and is computationally expensive, in terms of
processing speed, memory usage, and disk input/output.
The data reduction software is designed to be mostly run as an automated pipeline and to fit into the open source
environment of the ESO data flow as well as into a data management system based on AstroWISE. We describe the
functionality of the pipeline, highlight details of new and unorthodox processing steps, discuss which algorithms and code
could be used from other projects. Finally, we show the performance on both laboratory data as well as simulated scientific
data.
HARMONI is a visible and near-IR integral field spectrograph, providing the E-ELT's spectroscopic capability at first
light. It obtains simultaneous spectra of 32000 spaxels, at a range of resolving powers from R~4000 to R~20000,
covering the wavelength range from 0.47 to 2.45 μm. The 256 × 128 spaxel field of view has four different plate scales,
with the coarsest scale (40 mas) providing a 5″ × 10″ FoV, while the finest scale is a factor of 10 finer (4mas).
We describe the opto-mechanical design of HARMONI, prior to the start of preliminary design, including the main subsystems
- namely the image de-rotator, the scale-changing optics, the splitting and slicing optics, and the spectrographs.
We also present the secondary guiding system, the pupil imaging optics, the field and pupil stops, the natural guide star
wavefront sensor, and the calibration unit.
The Multi Unit Spectroscopic Explorer (MUSE) instrument is a second-generation integral-field spectrograph
in development for the Very Large Telescope (VLT), operating in the visible and near IR wavelength range
(465-930 nm). Given the complexity of MUSE we have developed an instrument numerical simulator, which
includes the whole chain of acquisition from the atmosphere down to the telescope and including the detectors,
and taking into account both optical aberrations and diffraction effects, by propagating a wavefront through
the instrument, according to the Fourier optics concept.
This simulator is used to produce simulated exposures, in order to develop the data reduction software
and to develop and validate the test procedures of the assembly, integration and tests phase. The MUSE
instrument is currently being integrated in CRAL, and first real exposures have been taken. This paper
compares and analyses the differences between the real data and the numerical simulations, in order to
improve the instrument simulator and make it more realistic.
MUSE (Multi Unit Spectroscopic Explorer) is an integral-field spectrograph which will be mounted on the Very Large
Telescope (VLT). MUSE is being built for ESO by a European consortium under the supervision of the Centre de
Recherche Astrophysique de Lyon (CRAL).
In this context, CRAL is responsible for the development of dedicated software to help MUSE users prepare and submit
their observations. This software, called MUSE-PS, is based on the ESO SkyCat tool that combines visualization of
images and access to catalogs and archive data for astronomy. MUSE-PS has been developed as a plugin to SkyCat to
add new features specific to MUSE observations.
In this paper, we present the MUSE observation preparation tool itself and especially its specific functionalities:
definition of the center of the MUSE field of view and orientation, selection of the VLT guide star for the different
modes of operations (Narrow Field Mode or Wide Field Mode, with or without AO). We will also show customized
displays for MUSE (zoom on specific area, help with MUSE mosaïcing and generic offsets, finding charts …).
The Multi-Unit Spectroscopic Explorer (MUSE), an integral-field spectrograph for the ESO Very Large Telescope, has
been built and integrated by a consortium of 7 European institutes. MUSE can simultaneously record spectra across a
field of view of 1 square arcminute in the wavelength range from 465nm to 930nm. The calibration unit (CU) for MUSE
was developed to provide accurate flat fielding, spectral, geometrical, image quality and efficiency calibration for both
the wide-field and AO-assisted narrow-field modes. This paper describes the performance of the CU and electronics,
from the subsystem validation to the integration, alignment and use in the MUSE instrument.
MUSE (Multi Unit Spectroscopic Explorer) is a second generation instrument developed for ESO (European Southern
Observatory) and will be assembled to the VLT (Very Large Telescope) in 2013. The MUSE instrument can
simultaneously record 90.000 spectra in the visible wavelength range (465-930nm), across a 1*1arcmin² field of view,
thanks to 24 identical Integral Field Units (IFU). A collaboration of 7 institutes has partly validated and sent their subsystems
to CRAL (Centre de Recherche Astrophysique de Lyon) in 2011, where they have been assembled together.
The global test and validation process is currently going on to reach the Preliminary Acceptance in Europe in 2012. The
sharing of performances has been based on 5 main functional sub-systems. The Fore Optics sub-system derotates and
anamorphoses the VLT Nasmyth focal plane image, the Splitting and Relay Optics associated with the Main Structure
are feeding each IFU with 1/24th of the field of view. Each IFU is composed of a 3D function insured by an image slicer
system and a spectrograph, and a detection function by a 4k*4k CCD cooled down to 163°K. The 5th function is the
calibration and data reduction of the instrument. This article depicts the sequence of tests that has been completely
reshafled mainly due to planning constraints. It highlights the priority given to the most critical performances tests of the
sub-systems and their results. It enhances then the importance given to global tests. Finally, it makes a status on the
verification matrix and the validation of the instrument and gives a critical view on the risks taken.
Optical coatings are one of the key elements of the VLT’s second generation instrument MUSE. The Multi Unit
Spectroscopic Explorer is developed for the European Southern Observatory (ESO) and will be installed in 2013 at the
VLT (Very Large Telescope). MUSE is a panoramic integral field spectrograph (1x1arcmin² Field of View) operating in
the visible wavelength range (465 nm - 930 nm). The throughput, which strongly depends on the optical coatings, is one
of the most important parameters of the MUSE instrument, which aims at observing very faint objects.
This article focuses on the different refractions and reflections required by the optical design of MUSE. Between the
output of the VLT and the final detectors of MUSE, photons are typically reflected 7 times by mirrors and transmitted 26
times through antireflective coatings. A comparison between metallic and multi-dielectric coatings is presented here in
order to explain the best compromise that has been chosen for MUSE purpose. High reflective multi-dielectric coatings
of large bandwidth are rather thick and induce significant stress on the substrate which may bend the substrate. This
deformation of mirrors is simulated and compared to measurements on MUSE optics. Finally, systematic optical coating
tests have been conducted, so as to check the durability under severe conditions such as humidity, temperature change,
abrasion.
In the end, the choice of high quality optical coatings should allow MUSE to reach a global throughput higher than 40%.
The resolution of ground-based telescopes is dramatically limited by the atmospheric turbulence.. Adaptative optics
(AO) is a real-time opto-mechanical approach which allows to correct for the turbulence effect and to reach the ultimate
diffraction limit astronomical telescopes and their associated instrumentation.
Nevertheless, the AO correction is never perfect especially when it has to deal with large Field of View (FoV). Hence, a
posteriori image processing really improves the final estimation of astrophysical data. Such techniques require an
accurate knowledge of the system response at any position in the FoV
The purpose of this work is then the estimation of the AO response in the particular case of the MUSE [1] /GALACSI
[2] instrument (a 3D mult-object spectrograph combined with a Laser-assisted wide field AO system which will be
installed at the VLT in 2013). Using telemetry data coming from both AO Laser and natural guide stars, a Point Spread
Function (PSF) is derived at any location of the FoV and for every wavelength of the MUSE spectrograph.
This document presents the preliminary design of the MUSE WFM PSF reconstruction process. The various hypothesis
and approximations are detailed and justified. A first description of the overall process is proposed. Some alternative
strategies to improve the performance (in terms of computation time and storage) are described and have been
implemented. Finally, after a validation of the proposed algorithm using end-to-end models, a performance analysis is
conducted (with the help of a full end-to-end model). This performance analysis will help us to populate an exhaustive
error budget table.
HARMONI has been conceived as a workhorse visible and near-infrared (0.47-2.45 microns) integral field spectrograph
for the European Extremely Large Telescope (E-ELT). It provides both seeing and diffraction limited observations at
several spectral resolutions (R= 4000, 10000, 20000). HARMONI can operate with almost any flavor of AO (e.g.
GLAO, LTAO, SCAO), and it is equipped with four spaxel scales (4, 10, 20 and 40 mas) thanks to which it can be
optimally configured for a wide variety of science programs, from ultra-sensitive observations of point sources to highangular
resolution spatially resolved studies of extended objects. In this paper we describe the expected performance of
the instrument as well as its scientific potential. We show some simulated observations for a selected science program,
and compare HARMONI with other ground and space based facilities, like VLT, ALMA, and JWST, commenting on
their synergies and complementarities.
MUSE (Multi Unit Spectroscopic Explorer) is a second generation instrument developed for ESO (European Southern
Observatory) to be installed on the VLT (Very Large Telescope) in year 2012. The MUSE project is supported by a
European consortium of 7 institutes. After a successful Final Design Review the project is now facing a turning point
which consist in shifting from design to manufacturing, from calculation to test, ... from dream to reality.
At the start, many technical and management challenges were there as well as unknowns. They could all be derived of
the same simple question: How to deal with complexity? The complexity of the instrument, of the work to de done, of
the organization, of the interfaces, of financial and procurement rules, etc.
This particular moment in the project life cycle is the opportunity to look back and evaluate the management methods
implemented during the design phase regarding this original question. What are the lessons learn? What has been
successful? What could have been done differently? Finally, we will look forward and review the main challenges of the
MAIT (Manufacturing Assembly Integration and Test) phase which has just started as well as the associated new
processes and evolutions needed.
The Multi Unit Spectroscopic Explorer (MUSE) instrument is a second-generation integral-field spectrograph
in development for the Very Large Telescope (VLT), operating in the visible and near IR wavelength range
(465-930 nm). Given the complexity of MUSE we have developed a numerical model of the instrument, which
includes the whole chain of acquisition from the atmosphere down to the telescope and including the detectors,
and taking into account both optical aberrations and diffraction effects. Simulating atmospheric effects such as
turbulence, refraction and sky background within an instrument numerical simulator is computation intensive,
and the simulation of these effects is usually beyond the scope of an instrument simulator as it is done in
dedicated simulations from which only the results are available. In this paper we describe how these effects are
simulated in the VLT/MUSE numerical simulator, the simplifications that are used, as well as the assumptions
leading to these simplifications.
MUSE (Multi Unit Spectroscopic Explorer) is a second generation instrument developed for ESO (European Southern Observatory) and will be assembled to the VLT (Very Large Telescope) in 2012. The MUSE instrument can simultaneously record 90.000 spectra in the visible wavelength range (465-930nm), across a 1*1arcmin2 field of view, thanks to 24 identical Integral Field Units (IFU). A collaboration of 7 institutes has successfully passed the Final Design Review and is currently working on the first sub-assemblies. The sharing of performances has been based on 5 main functional sub-systems. The Fore Optics sub-system derotates and anamorphoses the VLT Nasmyth focal plane image, the Splitting and Relay Optics associated with the Main Structure are feeding each IFU with 1/24th of the field of view.
Each IFU is composed of a 3D function insured by an image slicer system and a spectrograph, and a detection function
by a 4k*4k CCD cooled down to 163°K. The 5th function is the calibration and data reduction of the instrument. This
article depicts the breakdown of performances between these sub-systems (throughput, image quality...), and underlines
the constraining parameters of the interfaces either internal or with the VLT. The validation of all these requirements is a
critical task started a few months ago which requires a clear traceability and performances analysis.
The second generation instrument MUSE (Multi Unit Spectroscopic Explorer) developed for the VLT (Very Large
Telescope) for ESO (European Southern Observatory) is composed of 24 identical Integral Field Unit. To perform the
tests and the integration in a shorter time, we have developed an opto-mechanical system of AIT Tools (Assembly-
Integration-Test) referenced to an unique simulator of IFU. Each IFU sub system and its test bench (sources, image
slicer, spectrograph, IFU) are checked with respect to the same opto-mechanical references. These references are also
used to align all the 24 IFU onto the MUSE main structure. The system allows a better homogeneity between IFU in
term of performances and a better traceability between its sub-systems. This paper presents the different AIT tools
developed at CRAL to reach the specified performances for the serial phase of AIT of 24 IFU.
The Multi-Unit Spectroscopic Explorer (MUSE) is an integral-field spectrograph for the ESO Very Large Telescope.
After completion of the Final Design Review in 2009, MUSE is now in its manufacture and assembly phase. To achieve
a relative large field-of-view with fine spatial sampling, MUSE features 24 identical spectrograph-detector units. The
acceptance tests of the detector sub-systems, the design and manufacture of the calibration unit and the development of
the Data Reduction Software for MUSE are under the responsibility of the AIP. The optical design of the spectrograph
implies strict tolerances on the alignment of the detector systems to minimize aberrations. As part of the acceptance
testing, all 24 detector systems, developed by ESO, are mounted to a MUSE reference spectrograph, which is illuminated
by a set of precision pinholes. Thus the best focus is determined and the image quality of the spectrograph-detector
subsystem across wavelength and field angle is measured.
MUSE (Multi Unit Spectroscopic Explorer) is a second generation VLT panoramic integral field spectrograph
developed for the European Southern Observatory (ESO), operating in the visible wavelength range (0.465-0.93 μm). It
is composed of 24 identical Integral Field Units (IFU); each one incorporates an advanced image slicer associated with a
classical spectrograph and a detector vessel. The Image Slicer subsystem -ISS- is composed of two mirror arrays of 48
spherical elements each. It is made of Zerodur and uses an innovative polishing approach where all individual
components are polished together by classical method. The MUSE Spectrograph -SPS-, with fast output focal ratio of
f/1.95, implements a Volume Phase Holographic Grating - VPHG. The last subsystem, the Detector Vessel -DV- includes
a chip of 4k by 4k 15μm pixels supported by a Vacuum and Cryogenic System - VCS - provided by ESO.
The first out of 24 IFUs for MUSE instrument has been manufactured, aligned and tested last months. First, this paper
describes the optical design, the manufacturing and test results (image quality, pupil and field of view positioning) of
each subsystem independently. Second, we will focus on overall system performance (image quality and positioning) of
the spectrograph associated with the detector vessel. At the end, the test results (image quality, positioning, throughput,
mechanical interfaces) of the first IFU for MUSE instrument will be reported.
Most of them are compliant with requirements that it demonstrates that the manufacturing, integration, alignment and
tests processes are mature and gives good confidence for serial production by 24 times applied to MUSE instrument.
ERASMUS-F is a pathfinder study for a possible E-ELT 3D-instrumentation, funded by the German Ministry for
Education and Research (BMBF). The study investigates the feasibility to combine a broadband optical spectrograph
with a new generation of multi-object deployable fibre bundles. The baseline approach is to modify the spectrograph of
the Multi-Unit Spectroscopic Explorer (MUSE), which is a VLT integral-field instrument using slicers, with a fibre-fed
input. Taking advantage of recent developments in astrophotonics, it is planed to equip such an instrument with fused
fibre bundles (hexabundles) that offer larger filling factors than dense-packed classical fibres.
The overall project involves an optical and mechanical design study, the specifications of a software package for 3Dspectrophotometry,
based upon the experiences with the P3d Data Reduction Software and an investigation of the
science case for such an instrument. As a proof-of-concept, the study also involves a pathfinder instrument for the VLT,
called the FIREBALL project.
Volume Phase Holographic Gratings (VPHG) are key elements for the second generation instrument MUSE (Multi Unit
Spectroscopic Explorer) developed for the VLT (Very Large Telescope) for ESO (European Southern Observatory).
MUSE operates in the visible wavelength range (465-930nm) and is composed of 24 spectrographs including one VPHG
each. This article briefly describes the design of the grating manufactured by Kaiser Optical Systems, to reach the MUSE
spectral resolution and efficiency. On the other hand the set up developed in CRAL (Centre de Recherche Astrophysique
de Lyon) to test the VPHG final performance is deeply discussed. This set up uses a broadband source coupled to a
monochromator, and a compensation arm to remove the source intensity fluctuations. The source is amplitude modulated
by a chopper, and a lock-in amplifier extracts the modulated signal from the photodiodes.
The measurement arm scans the 0, 1st and 2nd diffraction orders of the grating and allows tests of different areas over its
whole surface of 120mm*60mm. The accuracy reached is below one percent in efficiency, allows us to validate the
performance and its uniformity over the surface of the gratings.
Niranjan Thatte, Mathias Tecza, Fraser Clarke, Roger Davies, Alban Remillieux, Roland Bacon, David Lunney, Santiago Arribas, Evencio Mediavilla, Fernando Gago, Naidu Bezawada, Pierre Ferruit, Ana Fragoso, David Freeman, Javier Fuentes, Thierry Fusco, Angus Gallie, Adolfo Garcia, Timothy Goodsall, Felix Gracia, Aurelien Jarno, Johan Kosmalski, James Lynn, Stuart McLay, David Montgomery, Arlette Pecontal, Hermine Schnetler, Harry Smith, Dario Sosa, Giuseppina Battaglia, Neil Bowles, Luis Colina, Eric Emsellem, Ana Garcia-Perez, Szymon Gladysz, Isobel Hook, Patrick Irwin, Matt Jarvis, Robert Kennicutt, Andrew Levan, Andy Longmore, John Magorrian, Mark McCaughrean, Livia Origlia, Rafael Rebolo, Dimitra Rigopoulou, Sean Ryan, Mark Swinbank, Nial Tanvir, Eline Tolstoy, Aprajita Verma
We describe the results of a Phase A study for a single field, wide band, near-infrared integral field spectrograph for the
European Extremely Large Telescope (E-ELT). HARMONI, the High Angular Resolution Monolithic Optical & Nearinfrared
Integral field spectrograph, provides the E-ELT's core spectroscopic requirement. It is a work-horse instrument,
with four different spatial scales, ranging from seeing to diffraction-limited, and spectral resolving powers of 4000,
10000 & 20000 covering the 0.47 to 2.45 μm wavelength range. It is optimally suited to carry out a wide range of
observing programs, focusing on detailed, spatially resolved studies of extended objects to unravel their morphology,
kinematics and chemical composition, whilst also enabling ultra-sensitive observations of point sources.
We present a synopsis of the key science cases motivating the instrument, the top level specifications, a description of
the opto-mechanical concept, operation and calibration plan, and image quality and throughput budgets. Issues of
expected performance, complementarity and synergies, as well as simulated observations are presented elsewhere in
these proceedings[1].
Summary: The Multi Unit Spectroscopic Explorer (MUSE) is a second-generation VLT panoramic integral-field
spectrograph currently in manufacturing, assembly and integration phase. MUSE has a field of 1x1 arcmin2 sampled at
0.2x0.2 arcsec2 and is assisted by the VLT ground layer adaptive optics ESO facility using four laser guide stars. The
instrument is a large assembly of 24 identical high performance integral field units, each one composed of an advanced
image slicer, a spectrograph and a 4kx4k detector. In this paper we review the progress of the manufacturing and report
the performance achieved with the first integral field unit.
An image slicer breadboard has been designed, manufactured and tested for MUSE (Multi Unit Spectroscopic Explorer)
instrument, a second generation integral field spectrograph developed for the European Southern Observatory (ESO) for
the VLT. MUSE is operating in the visible and near IR wavelength range (0.465-0.93 μm) and is composed of 24
identical Integral Field Units; each one incorporates an advanced image slicer associated with a classical spectrograph.
This paper describes the original optical design, the manufacturing, component test results (shape, roughness,
reflectivity, microscopic visualization) and overall system performance (image quality, alignment) of the image slicer
breadboard. This one is a combination of two mirror arrays of 48 elements each. It is made of Zerodur and uses a new
polishing approach where all individual optical components are polished together by classical method. This image slicer
constitutes the first one which has the largest number of active slices (48) associated with strict tolerances in term of
positioning. The main results of the tests on this image slicer breadboard will then be presented. Most of them are
compliant with requirements. This demonstrates that the manufacturing process is mature and gives good confidence for
serial production applied to MUSE instrument.
The Multi-Unit Spectroscopic Explorer (MUSE) is an integral-field spectrograph for the VLT for the next decade. Using
an innovative field-splitting and slicing design, combined with an assembly of 24 spectrographs, MUSE will provide
some 90,000 spectra in one exposure, which cover a simultaneous spectral range from 465 to 930nm. The design and
manufacture of the Calibration Unit, the alignment tests of the Spectrograph and Detector sub-systems, and the
development of the Data Reduction Software for MUSE are work-packages under the responsibility of the AIP, who is a
partner in a European-wide consortium of 6 institutes and ESO, that is led by the Centre de Recherche Astronomique de
Lyon. MUSE will be operated and therefore has to be calibrated in a variety of modes, which include seeing-limited and
AO-assisted operations, providing a wide and narrow-field-of-view. MUSE aims to obtain unprecedented ultra-deep 3D-spectroscopic
exposures, involving integration times of the order of 80 hours at the VLT. To achieve the corresponding
science goals, instrumental stability, accurate calibration and adequate data reduction tools are needed. The paper
describes the status at PDR of the AIP related work-packages, in particular with respect to the spatial, spectral, image
quality, and geometrical calibration and related data reduction aspects.
The Multi Unit Spectroscopic Explorer (MUSE) instrument is a second-generation integral-field spectrograph
in development for the Very Large Telescope (VLT), operating in the visible and near IR wavelength range
(465-930 nm). Given the complexity of MUSE we have developed a numerical model of the instrument, which
includes the whole chain of acquisition from the atmosphere down to the telescope and including the detectors,
and taking into account both optical aberrations and diffraction effects. In this paper we present the software,
discuss the problems that have been encountered and the solutions that have been implemented, and we
conclude by presenting examples of simulations.
Glass and metallic image slicer breadboards have been designed, manufactured and tested for MUSE (Multi Unit
Spectroscopic Explorer) instrument, a second generation integral field spectrograph developed for the European
Southern Observatory (ESO) for the VLT. MUSE is operating in the visible and near IR wavelength range (0.465-0.93
μm) and is composed of 24 identical integral field units; each one incorporates an advanced image slicer associated with
a classical spectrograph.
This presentation describes the optical design, the manufacturing, component test results (shape, roughness, Bidirectional
Reflection Distribution Function - BRDF) and overall system performance (image quality, alignment) of two image
slicer breadboards. The first one is made of Zerodur and uses individual optical components polished by a classical
method and assembled together by molecular adhesion. This breadboard is a combination of mirrors and mini-lens
arrays. The second one is made of metal (copper or invar) using monolithic or segmented optical elements and state-ofthe-
art diamond-turning machines. It is composed of two sets of reflective mirrors.
We will then conclude with a comparison between these two different breadboards by choosing the most suitable
solution for the 24 MUSE image slicers.
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).
The Adaptive Optics Facility is a project to convert one VLT-UT into a specialized Adaptive Telescope. The present
secondary mirror (M2) will be replaced by a new M2-Unit hosting a 1170 actuators deformable mirror. The 3 focal
stations will be equipped with instruments adapted to the new capability of this UT. Two instruments are in
development for the 2 Nasmyth foci: Hawk-I with its AO module GRAAL allowing a Ground Layer Adaptive Optics
correction and MUSE with GALACSI for GLAO correction and Laser Tomography Adaptive Optics correction. A
future instrument still needs to be defined for the Cassegrain focus. Several guide stars are required for the type of
adaptive corrections needed and a four Laser Guide Star facility (4LGSF) is being developed in the scope of the AO
Facility. Convex mirrors like the VLT M2 represent a major challenge for testing and a substantial effort is dedicated to
this. ASSIST, is a test bench that will allow testing of the Deformable Secondary Mirror and both instruments with
simulated turbulence. This article describes the Adaptive Optics facility systems composing associated with it.
The Multi Unit Spectroscopic Explorer (MUSE) is a second-generation VLT panoramic integral-field spectrograph under preliminary design study. MUSE has a field of 1x1 arcmin2 sampled at 0.2x0.2 arcsec2 and is assisted by the VLT ground layer adaptive optics ESO facility using four laser guide stars. The simultaneous spectral range is 0.465-0.93 μm, at a resolution of R~3000. MUSE couples the discovery potential of a large imaging device to the measuring capabilities of a high-quality spectrograph, while taking advantage of the increased spatial resolution provided by adaptive optics. This makes MUSE a unique and tremendously powerful instrument for discovering and characterizing objects that lie beyond the reach of even the deepest imaging surveys. MUSE has also a high spatial resolution mode with 7.5x7.5 arcsec2 field of view sampled at 25 milli-arcsec. In this mode MUSE should be able to obtain diffraction limited data-cubes in the 0.6-0.93 μm wavelength range. Although the MUSE design has been optimized for the study of galaxy formation and evolution, it has a wide range of possible applications; e.g. monitoring of outer planets atmosphere, environment of young stellar objects, super massive black holes and active nuclei in nearby galaxies or massive spectroscopic surveys of stellar fields in the Milky Way and nearby galaxies.
MUSE (Multi Unit Spectroscopic Explorer) is a second generation integral field spectrograph proposed to the European Southern Observatory (ESO) for the VLT. MUSE combines a 1' x 1' Field of View (FoV) with a spectral resolution going to 3000 and a spatial resolution of 0.2" provided by the GALACSI adaptive optics system. MUSE is operating in the visible and near IR wavelength range (0.465-0.93 μm). It is composed of 24 identical integral field units; each one incorporates an advanced image slicer made of a combination of mirrors and mini-lenses arrays. During the feasibility study, a slicer prototype has been designed, manufactured and tested. This paper firstly describes an original approach for the slicer optical design and manufacturing. Then, we will focus on the optical tests of the prototype. These tests included the control of the angular tilts and assembling method of the slicer, the measurements of the position, size and shape of the pseudo-slits, the measurements of the Point Spread Function (PSF) for the slice-slit imagery on the whole FoV and an estimation of the size of the global exit pupil. We finally conclude on the feasibility of MUSE image slicer and its possible improvement for the next design phase.
Designs for Extremely Large Telescopes (ELTs) are quite well advanced, but the requirements of instruments have had limited impact. Since provision of a suitable environment for instruments is a critical aspect of all telescopes, we outline some well-known and some less-appreciated challenges of designing instruments for ELTs. A wide-field spectrometer (WFSPEC) with ~10 arcmin field-of-view, probably with AO correction of ground-layer seeing, illustrates the well-known difficulty of matching modern detector pixels to large (~0."3) images. The challenges of exploiting wide-field (1'-2' FOV) high-performance AO systems on ELTs are illustrated by a Multi-Object Multi-field Spectrometer and Imager (MOMSI), which provides imaging and integral-field spectroscopy, at near-diffraction-limited pixel scales, of targets in approximately 300 subfields each. This instrument, roughly equivalent to all the astronomical spectrometers yet built, extracts ~200 times less of the available information from the ELT's FOV than near-future instruments on 8-m class telescopes will do for their hosts. We emphasise the great size of such instruments (40-100 tonnes, 100-200 m3) and the need to accommodate this size in telescope plans. A third area of challenge is the exploitation of the potential capabilities of ELTs in the mid-IR, where they would offer powerful complements to JWST and ALMA; low-emissivity telescope designs and, possibly, cryogenic AO, may be needed. Finally, we outline the potential challenges of correcting atmospheric dispersion effects.
The MUSE (Multi Unit Spectroscopic Explorer) instrument is a second-generation integral-field spectrograph candidate for the VLT, operating in the visible and near IR wavelength range (0.465 - 0.93 μm). It is combining a large 1' x 1' Field of View with a spectral resolution of 3000 and a spatial resolution of 0.2" coupled to a sophisticated ground-layer Adaptive Optics (AO) system. After a brief summary of the major instrumental requirements, we will focus on the opto-mechanical design of MUSE, including core subsystems such as the Fore-Optics, the Image Slicers and the Spectrographs, the Structure and the Calibration Unit. The most creative trends of the instrument will be underlined, such as the specific choices adopted to reduce the costs, weight and volume of the Slicer and Spectrograph units, that need to be manufactured and installed on the VLT Nasmyth platform into twenty-four replicas. Finally, a realistic estimate of the expected performance (in both throughput and image quality), and the future development program for the forthcoming detailed design phase will be presented.
By incorporating spatial coverage with the spectral dimension,
integral-field spectroscopy is uniquely suited for exploiting the
capabilities of adaptive optics (AO) systems. OASIS is a lenslet-based integral-field spectrograph designed to perform high-resolution
observations on AO-corrected sources, operating at visible
wavelengths. This instrument was commissioned at the William Herschel
Telescope, La Palma, in July 2003 to work with the ING's AO system,
NAOMI. Here we present an overview of the capabilities of the
OASIS+NAOMI system, and show results obtained using this technique. The science presented here is a small preview of what will be possible for a large number of objects when the GLAS laser guide system is operational.
The Multi Unit spectroscopic Explorer (MUSE) is a second generation VLT panoramic integral-field spectrograph operating in the visible wavelength range. MUSE has a field of 1 x 1 arcmin2 sampled at 0.2x0.2 arcsec2 and is assisted by a ground layer adaptive optics system using four laser guide stars. The simultaneous spectral range is 0.465-0.93 μm, at a resolution of R~3000. MUSE couples the discovery potential of a large imaging device to the measuring capabilities of a high-quality spectrograph, while taking advantage of the increased spatial resolution provided by adaptive optics. This makes MUSE a unique and tremendously powerful instrument for discovering and characterizing objects that lie beyond the reach of even the deepest imaging surveys. MUSE has also a high spatial resolution mode with 7.5 x 7.5 arcse2 field of view sampled at 25 milli-arcsec. In this mode MUSE should be able to get diffraction limited data-cube in the 0.6-1 μm wavelength range. Although MUSE design has been optimized for the study of galaxy formation and evolution, it has a wide range of possible applications; e.g. monitoring of outer planets atmosphere, young stellar objects environment, supermassive black holes and active nuclei in nearby galaxies or massive spectroscopic survey of stellar fields.
Plans for a European Extremely Large Telescope are quite well advanced. However examination of instrument designs has thus far been directed only at covering the anticipated science requirements and has had little impact on telescope design considerations. Nevertheless, the provision of a suitable environment for instruments is a critical part of the design of all large telescopes. We illustrate this point with examples from recent experience. A Work Package, part of a proposed Design Study for a European ELT under the European Union's Framework Programme 6 (FP6), will explore this issue, while also developing designs for a scientifically credible instrument suite. For three instruments mechanical and optical design studies will be carried out in sufficient detail clearly to identify design drivers for the telescope. These are a wide-field seeing limited or ground-layer AO-corrected (GLAO) optical/NIR spectrometer, WFSPEC; an MCAO-corrected O/NIR Multi-Object Multi-field Spectrometer-Imager, MOMSI, which offers particularly daunting challenges; and a mid-infrared high-resolution AO-corrected Imager-Spectrometer instrument, MIDIR. Five instrument designs will be examined in less detail: an extreme-AO (XAO) corrected coronagraphic imager-spectrometer known as Planet Finder (the goal of which is the detection and characterization of terrestrial exo-planets); a very high resolution spectrometer, HISPEC; a high time-resolution instrument, HITRI, intended to allow photometry, polarimetry and phase-resolved spectroscopy of faint rapidly varying objects; a fast-response broad-band multi-function instrument known as GRB-catcher; and a sub-millimeter imager, SCUBA-3. A separate small study will seek innovative designs not included in the main suite. Another will initiate the program by examining the requirements of atmospheric dispersion correction (ADC) for 30 to 100-m diffraction-limited telescopes, which may require active sensing and, possibly, "adaptive" correction on atmospheric turbulence timescales. All these studies -- except that of SCUBA3 -- will require support from Adaptive Optics studies, as most instruments will be utterly dependent on AO: close communication between instrument and AO groups is essential, here and in general.
The introduction of Image Slicers in Astronomy has been growing rapidly in the recent years. These optical devices allow the simultaneous observation on the same detector matrix of two-dimensional sky maps and the spectral decomposition of light on all of their angular samples, therefore dramatically reducing the observation times and getting rid of the spectro-photometric variations of the atmosphere. Today the implementation of Image Slicers is planned on various ground and space telescopes, covering a spectral domain ranging from blue to mid-IR wavelengths. Among such different projects, we describe the Image Slicer of MUSE (Multi Unit Spectroscopic Explorer), a second-generation Integral-Field Spectrograph for the VLT combining a 1’ x 1’ Field of View with a spatial resolution of 0.2” and a spectral resolution of 3000. The most efficient principle of an Image Slicer consists in a combination of several different optical channels, each made of three mini-mirrors having different tilts and curvatures. After a brief presentation of the MUSE Image Slicer requirements, we will explain the followed logic in order to optimize the opto-mechanical design and cost of the Slicer: indeed one of MUSE peculiarity is the total number of its individual modules, that is 24. The realization of such series at an affordable cost actually is a design driver of the study. The communication also deals with the used optical design models, the expected performance, the candidate technologies for the manufacturing of all the components, and the future development of a prototype of this critical optical subsystem.
Francois Henault, Roland Bacon, Christophe Bonneville, Didier Boudon, Roger Davies, Pierre Ferruit, Gerard Gilmore, Oliver LeFevre, Jean-Pierre Lemonnier, Simon Lilly, Simon Morris, Eric Prieto, Matthias Steinmetz, P. Tim de Zeeuw
We describe MUSE (Multi Unit Spectroscopic Explorer), a second-generation integral-field spectrograph for the VLT, operating in the visible and near IR wavelength range. It combines a 1' x 1' Field of View with the improved spatial resolution (0.2") provided by adaptive optics and covers a large simultaneous spectral range (0.48 - 1 μm). With this unique combination of capabilities, MUSE has a wide domain of application, and a large discovery potential. It will provide ultra deep fields with a limiting magnitude for spectroscopy of R = 28. After a brief presentation of the scientific case and the derived instrument requirements, we will focus on the MUSE optical design, including the overall architecture, the major trade-off that were conducted in order to optimize the cost and performance, and a provisional implementation scheme of the instrument on the VLT Nasmyth platform. Then the most important optical subsystems (as the 3 x 8 Field-splitter, the Image Slicers and the Spectrometers) are described. One of MUSE special feature is the impressive number of Image Slicer and Spectrometer modules which must be manufactured, that is 24. The realization of such series has been studied in collaboration with an industrial company. Finally a preliminary estimation of the expected performance and a technological development program in order to secure the realization of the critical optical subsystems will be presented.
We are proposing to implement an integral field unit in NIRSPEC the Near Infra-Red Spectrograph for the NGST. This unique IFU will cover a 2x2 arcsec^2 field of view sampled at 0.05" (or 3"x3" @0.07"). The spectral resolution will go up to 3000. We will present the optical design of this unit and its implementation inside the NIRSPEC instrument. We will also show the results from an analysis of the effects of diffraction and stray-light inside the module, as well as the original method of integration we are using.. This module will be built using the image slicer technology, including 40 slices, each 900μm thick. We are also developing an innovative mechanical structure for this unit including the magnifying optics and the slicer itself, providing a very compact unit. The implementation will have a small impact on the NIRSPEC instrument, with only one to three additional gratings to be implemented in the grating wheel. The limiting magnitude of this mode should reach AB=24-26 for a point source. This unit would provide, for a marginal cost, a unique opportunity to offer a very powerful 3D spectrograph on NGST. The NIRSPEC instrument is under the ESA responsibility, and this work is being conducted in the context of the Astrium-ESA phase A study to which we are participating.
A research and development activity on an Image Slicer System for Integral Field Spectroscopy is conducted with possible applications on future instrumentation for major ground-based (VLT second-generation instruments) and space (NGST, SNAP) observatories. These instruments need high-photometric accuracy, compactness and will possibly work under cryogenic environment, while multi-integral field units may require mass production. Several prototypes have been manufactured since March 2000. This paper provides an overview of the difficulties and limits of the design for different applications, and will describe technology developments and performance evaluation. In particular, the assembly of Zerodur micro-optical elements required an original method of assembly using high precision molecular adhesion, in order to comply with optical tolerances. Following the exact characteristics of the optical elements, diffraction and straylight analyses have been performed in the NIR range. It was found that diffraction effects due to the image slicer induce energy losses less than a few percents and do not induce any crosstalk between pseudo-slits. With a good baffling, scatter can be controlled to minimize the background increase to less than 10-4 times the incident flux.
Greg Aldering, G. Adam, P. Antilogus, Pierre Astier, R. Bacon, S. Bongard, C. Bonnaud, Y. Copin, Delphine Hardin, Francois Henault, Dale Howell, Jean-Pierre Lemonnier, Jean-Michel Levy, Stewart Loken, Peter Nugent, Reynald Pain, A. Pecontal, E. Pecontal, Saul Perlmutter, Robert Quimby, K. Schahmaneche, G. Smadja, W. Michael Wood-Vasey
The Nearby Supernova Factory (Snfactory) is an international experiment designed to lay the foundation for the next generation of cosmology experiments (such as CFHTLS, wP, SNAP and LSST) which will measure the expansion history of the Universe using Type Ia supernovae. The Snfactory will discover and obtain frequent lightcurve spectrophotometry covering 3200-10000Å for roughly 300 Type Ia supernovae at the low-redshift end of the smooth Hubble flow. The quantity, quality, breadth of galactic environments, and homogeneous nature of the Snfactory dataset will make it the premier source of calibration for the Type Ia supernova width-brightness relation and the intrinsic supernova colors used for K-correction and correction for extinction by host-galaxy dust. This dataset will also allow an extensive investigation of additional parameters which possibly influence the quality of Type Ia supernovae as cosmological probes. The Snfactory search capabilities and follow-up instrumentation include wide-field CCD imagers on two 1.2-m telescopes (via collaboration with the Near Earth Asteroid Tracking team at JPL and the QUEST team at Yale), and a two-channel integral-field-unit optical spectrograph/imager being fabricated for the University of Hawaii 2.2-m telescope. In addition to ground-based follow-up, UV spectra for a subsample of these supernovae will be obtained with HST. The pipeline to obtain, transfer via wireless and standard internet, and automatically process the search images is in operation. Software and hardware development is now underway to enable the execution of follow-up spectroscopy of supernova candidates at the Hawaii 2.2-m telescope via automated remote control of the telescope and the IFU spectrograph/imager.
BEAR is a high-resolution imaging FTS in operation on the CFH Telescope, obtained by the coupling of a step-scan FTS and a near IR camera. TIGER is a integral field spectrometer (IFS) for the visible, which was in operation at CFHT, in which a microlens array segments a small entrance field. A new version (OASIS() has been made to be used behind an adaptive optics system, leading to an even smaller field of view. By adapting a TIGER-type field segmentation on an imaging FTS, the instrument remains an IFS more versatile than each instrument taken separately. Such an instrument would be characterized by the access to the same spatial resolution, but on a field larger than with a TIGER instrument, a larger spectral coverage, a continuously chosen spectral resolution as in an FTS, and a better sensitivity than a BEAR instrument. For that, a mosaic of microlens array, made in an IR glass transparent between 1 and 5 microns, is paving one input port of a large field dual-output port interferometer which has a provision for a mirror travel of 5 mm, giving the choice for a resolution up to 104 at 1.7 micrometers . A prism on each output beam disperse the entrance points which are imaged on InSb array. A camera on each output beam records an image at each step of the FTS. This concept can be of interest for the instrumentation of a large ground-based telescope or better for a NGST.
Since the digital detectors (like CCDs) presently available for astronomical instruments have two dimensions only, there is an obvious problem for obtaining detailed spectroscopic information on extended astronomical objects (e.g. active galaxies, regions of star formation, globular clusters, etc.); the classical long- slit spectrographic techniques are grossly inadequate. Several so-called integral field spectrographs (IFS) have been used at the Canada-France-Hawaii telescope during the past years to improve this situation. They typically provide hundreds of spectra in a small (approximately 10' by 10') field with a subarcsecond spatial resolution capability and hundreds of spectral elements, both simultaneously accessed. We describe these various instruments and their present performances, review a few illustrative results obtained with CFH telescope and discuss the expected developments: use of IFS in combination with adaptive optics systems for the study of individual objects at spatial resolution near the 0.1' level, as well as their potential capabilities on Very Large Telescopes, with or without adaptive optics.
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