HARMONI is an Integral Field Spectrograph (IFS) for ESO’s ELT. It has been selected as the first light spec- trograph and will provide the workhorse spectroscopic capabilities for the ELT for many years. HARMONI is currently at the PDR-level and the current design for the HARMONI IFS consists of a number of spaxel scales sampling down to the diffraction limit of the telescope. It uses a field splitter and image slicer to divide the field into 4 sub-units, each providing an input slit to one of four nearly identical spectrographs. All spectrographs will operate at near infrared wavelengths (0.81-2.45 micrometers), sampling different parts of the spectrum with a range of spectral resolving powers (3300, 7000, 18000). In addition, two of the four spectrographs will have a Visible capability (0.5-0.83 micrometers) operating with seeing-limited observations. This proceeding presents an overview of the opto-mechanical design and specifications of the spectrograph units for HARMONI.
The European Southern Observatory (ESO) is building the Extremely Large Telescope (ELT), a 40-m class telescope to be installed on top of the 3046 m high mountain Cerro Armazones in the central part of Chile’s Atacama Desert. Once operational the ELT will be the largest optical/near-infrared telescope in the world. Powerful facility instruments that can deliver the science cases for the ELT are under development. The instrument roadmap lists more than six scientific instruments, each of them in the 15-35 tons range. While the telescope optics operate at ambient temperature, the instrument optics structure and in particular the detectors will be cooled to cryogenic temperatures down to as low as 4 Kelvin. ESO is aiming to implement proven technologies and commercial off-the-shelf components to build the cryogenic infrastructure for the ELT instruments. A combination of open loop Liquid Nitrogen cooling and low-vibration mechanical cryo-coolers will be installed to provide the required temperature levels and cooling capacities. ESO’s vacuum and cryogenic standards required major updates in order to match with the needs and challenges of this new class of huge instruments, each of them coming with up to 50 m<sup>3</sup> vessel volume and more than 5 tons cold mass.<p> </p> The paper outlines the instruments vacuum and cryogenic requirements, gives a brief overview of the ESO vacuum and cryogenic standards, and of the ELT cryogenic infrastructure baseline concept. The current testing approach for selected standard components such as low-vibration cryo-coolers and vibration damping systems will be presented.
SOXS (Son Of X-Shooter) will be a spectrograph for the ESO NTT telescope capable to cover the optical and NIR bands, based on the heritage of the X-Shooter at the ESO-VLT. SOXS will be built and run by an international consortium, carrying out rapid and longer term Target of Opportunity requests on a variety of astronomical objects. SOXS will observe all kind of transient and variable sources from different surveys. These will be a mixture of fast alerts (e.g. gamma-ray bursts, gravitational waves, neutrino events), mid-term alerts (e.g. supernovae, X-ray transients), fixed time events (e.g. close-by passage of minor bodies). While the focus is on transients and variables, still there is a wide range of other astrophysical targets and science topics that will benefit from SOXS. The design foresees a spectrograph with a Resolution-Slit product ≈ 4500, capable of simultaneously observing over the entire band the complete spectral range from the U- to the H-band. The limiting magnitude of R~20 (1 hr at S/N~10) is suited to study transients identified from on-going imaging surveys. Light imaging capabilities in the optical band (grizy) are also envisaged to allow for multi-band photometry of the faintest transients. This paper outlines the status of the project, now in Final Design Phase.
MATISSE (Multi AperTure mid-Infrared SpectroScopic Experiment) is the spectro-interferometer for the VLTI of the European Southern Observatory, operating in near and mid-infrared, and combining up to four beams from the unit or the auxiliary telescopes. MATISSE will offer new breakthroughs in the study of circumstellar environments by allowing the multispectral mapping of the material distribution, the gas and essentially the dust.<p> </p> The instrument consists in a warm optical system (WOP) accepting four optical beams and relaying them after a dichroic splitting (for the L and M- and N- spectral bands) to cold optical benches (COB) located in two separate cryostats. The Observatoire de la Côte d’Azur is in charge of the WOP providing the spectral band separation, optical path equalization and modulation, pupil positioning, beam anamorphosis, beam commutation, and calibration. NOVA-ASTRON is in charge of the COB providing the functions of beam selection, reduction of thermal background emission, spatial filtering, pupil transfer, photometry and interferometry splitting, additional beam anamorphosis, spectral filtering, polarization selection, image dispersion, and image combination. The Max Planck Institut für Radio Astronomie is in charge of the operation and performance validation of the two detectors, a HAWAII-2RG from Teledyne for the L- and M- bands and a Raytheon AQUARIUS for the N-band. Both detectors are provided by ESO. The Max Planck Institut für Astronomie is in charge of the electronics and the cryostats for which the requirements on space limitations and vibration stability resulted on very specific and stringent decisions on the design.<p> </p> The integration and test of the COB: the two cryogenic systems, including the cold benches and the detectors, have been conducted at MPIA in parallel with the integration of the WOP at OCA. At the end of 2014, the complete instrument was integrated at OCA. Following this integration, a period of interface and alignment between the COB and the WOP took place resulting in the first interference fringes in the L-band during summer 2015 and the first interference fringes in the N-ban in March 2016.<p> </p> After a period of optimization of both the instrument reliability and the environmental working conditions, the test plan is presently being conducted in order to evaluate the complete performance of the instrument and its compliance with the high-level requirements. The present paper gives the first results of the alignment, integration and test phase of the MATISSE instrument.
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?
GRAVITY is a second generation instrument for the VLT Interferometer, designed to enhance the near-infrared astrometric and spectro-imaging capabilities of VLTI. It will combine the AO corrected beams of the four VLT telescopes. The GRAVITY instrument uses a total of five eAPD detectors, four of which are for wavefront sensing and one for the Fringe tracker. In addition two Hawaii2RG are used, one for the acquisition camera and one for the spectrometer. A compact bath cryostat is used for each WFS unit, one for each of the VLT Unit Telescopes. Both Hawaii2RG detectors have a cutoff wavelength of 2.5 microns. A new and unique element of GRAVITY is the use of infrared wavefront sensors. For this reason SELEX-Galileo has developed a new high speed avalanche photo diode detector for ESO. The SAPHIRA detector, which stands for Selex Avalanche Photodiodes for Highspeed Infra Red Applications, has been already evaluated by ESO. At a frame rate of 1 KHz, a read noise of less than one electron can be demonstrated. A more detailed presentation about the performance of the SPAHIRA detector will be given at this conference 1. Each SAPHIRA detector is installed in an LN2 bath cryostat. The detector stage, filter wheel and optics are mounted on the cold plate of the LN2 vessel and enclosed by a radiation shield. All seven detector systems are controlled and read out by the standard ESO NGC controller. The NGC is a controller platform which can be adapted and customized for all infrared and optical detectors. This paper will discuss specific controller modifications implemented to meet the special requirements of the GRAVITY detector systems and give an overview of the GRAVITY detector systems and their performance.
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 arcmin<sup>2</sup> 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 Enhanced Resolution Imager and Spectrograph (ERIS) is the next-generation adaptive optics near-IR imager and
spectrograph for the Cassegrain focus of the Very Large Telescope (VLT) Unit Telescope 4, which will soon make full
use of the Adaptive Optics Facility (AOF). It is a high-Strehl AO-assisted instrument that will use the Deformable
Secondary Mirror (DSM) and the new Laser Guide Star Facility (4LGSF). The project has been approved for
construction and has entered its preliminary design phase. ERIS will be constructed in a collaboration including the Max-
Planck Institut für Extraterrestrische Physik, the Eidgenössische Technische Hochschule Zürich and the Osservatorio
Astrofisico di Arcetri and will offer 1 - 5 μm imaging and 1 - 2.5 μm integral field spectroscopic capabilities with a high
Strehl performance. Wavefront sensing can be carried out with an optical high-order NGS Pyramid wavefront sensor, or
with a single laser in either an optical low-order NGS mode, or with a near-IR low-order mode sensor. Due to its highly
sensitive visible wavefront sensor, and separate near-IR low-order mode, ERIS provides a large sky coverage with its 1’
patrol field radius that can even include AO stars embedded in dust-enshrouded environments. As such it will replace,
with a much improved single conjugated AO correction, the most scientifically important imaging modes offered by
NACO (diffraction limited imaging in the J to M bands, Sparse Aperture Masking and Apodizing Phase Plate (APP)
coronagraphy) and the integral field spectroscopy modes of SINFONI, whose instrumental module, SPIFFI, will be
upgraded and re-used in ERIS. As part of the SPIFFI upgrade a new higher resolution grating and a science detector
replacement are envisaged, as well as PLC driven motors. To accommodate ERIS at the Cassegrain focus, an extension
of the telescope back focal length is required, with modifications of the guider arm assembly. In this paper we report on
the status of the baseline design. We will also report on the main science goals of the instrument, ranging from exoplanet
detection and characterization to high redshift galaxy observations. We will also briefly describe the SINFONI-SPIFFI
upgrade strategy, which is part of the ERIS development plan and the overall project timeline.
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.
The 24 IFU from MUSE are equipped with 4K x 4K CCD detectors which are operated at cryogenic temperature around
160 K. The large size of the chip combined with a rather fast camera (F/2) impose strong positioning constrains. The
sensitive surface should remain in an angular envelope of less than 30 arc sec in both directions. The ambitious goal of
having the same spectrum format on every detector imposes also a very accurate positioning in the image plane. The
central pixel has to be located in a square smaller 50 microns relative to the external references.
The first part of the paper describes the mechanical design of the detector head. We concentrate on the various aspects of
the design with its very complex interfaces. The opto-mechanical concept is presented with an emphasis on the
robustness and reliability. We present also the necessary steps for the extreme optimization of the cryogenic performance
of this compact design driven with a permanent view of the production in series.
The techniques and procedures developed in order to meet and verify the very tight positioning requirements are
described in a second part. Then the 24 fully assembled systems undergo a system verification using one of the MUSE
spectrographs. These tests include a focus series, the determination of the PSF across the chip and a subsequent
calculation of the tip/tilt and shift rotation of the detector versus the optical axis.
MUSE with its 24 detectors distributed over an eight square meter vertical area was requiring a well engineered and
extremely reliable cryogenic system. The solution should also use a technology proven to be compatible with the very
high sensitivity of the VLT interferometer. A short introduction reviews the various available technologies to cool these 24 chips down to 160 K. The first part of the paper presents the selected concept insisting on the various advantages offered by LN2. In addition to the purely vacuum and cryogenic aspects we highlight some of the most interesting features given by the control system based on a PLC.
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.
In comparison to mechanical cryo-coolers, liquid nitrogen cooling has the double advantage to be free of vibration and to
remain not affected by power failure.
The paper reports about a very compact cryostat using a continuous circulation of liquid nitrogen which is provided from
an external storage tank. Since years, this cryostat is intensively used on the ESO VLT to cool either optical or Infra Red
After an introduction presenting the principle, the paper reports the performance of the cryostat recorded over many
years of utilization. We also present a few additional developments which allow the use of the cryostat for more exotic
applications such that Nasmyth rotating instruments or extremely stable radial velocity spectrograph. With the
construction of MUSE, a new era has started for this cryostat. The large multi IFU instrument requires 24 cryostats. The
last chapter of the paper describes this futurist system which is close to completion.
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 arcmin<sup>2</sup> sampled at
0.2x0.2 arcsec<sup>2</sup> 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.
REMIR is the NIR camera of the automatic REM (Rapid Eye Mount) Telescope located at ESO-La Silla Observatory (Chile) and dedicated to monitor the afterglow of Gamma Ray Burst events. During the last two years, the REMIR camera went through a series of cryogenics problems, due to the bad functioning of the Leybold cryocooler Polar SC7. Since we were unable to reach with Leybold for a diagnosis and a solution for such failures, we were forced to change drastically the cryogenics of REMIR, going from cryocooler to LN2: we adopted an <i>ad-hoc</i> modified Continuous Flow Cryostat, a cryogenics system developed by ESO and extensively used in ESO instrumentation, which main characteristic is that the LN2 vessel is separated from the cryostat, allowing a greater LN2 tank, then really improving the hold time. In this paper we report the details and results of this operation.
AMBER, Astronomical Multi BEam combineR, is the near-infrared focal instrument dedicated to the VLTI. It is designed to combine three of the VLTI Telescopes and to work simultaneously in the J, H and K spectral bands (1.0 to 2.4 μm).
The project successfully passed the Preliminary Acceptance in Europe in November 2003, resulting in the validation of the instrument laboratory performance1, of the compliance with the initial scientific specifications, and of the acceptance of ESO for AMBER to be part of the VLTI. After the transportation of the instrument to Paranal, Chile in January 2004, the Assembly Integration and Verification phase occurred mid-March to succeed with the first fringes observing bright stars with the VLTI siderostats.
This paper describes the different steps of the AIV and the first results in terms of instrumental stability, estimated visibility and differential phase.
AMBER is the focal near-infrared instrument of the VLTI combining
2 or 3 telescopes in the J, H and K bands with 3 spectral resolution modes. It uses single-mode fibers to ensure modal filtering and high measurement accuracies. AMBER has been integrated and tested in Grenoble during 2003. We report in this paper the lab performances of the instrument in terms of instrumental contrast, measurement accuracy and stability, and throughput.
The instrumentation for VLT/VLTI 1 facility of the European Southern Observatory at Paranal (Chile)includes the infrared beam-combiner called AMBER, that covers the near infrared bands up to 2.5 μm. The cold spectrograph we describe is the AMBER subsystem responsible of wavelength analysis and several other functions, all of them performed by means of optics, analyzers, and mechanisms working at the temperature of liquid nitrogen boiling at atmospheric pressure. The cryo-mechanical design of the spectrograph we describe here
used extensively the methods of finite element analysis and the laboratory tests validated this approach. The final optical quality we measured in the laboratory before shipping the instrument to Grenoble or integration (December 2002),is well inside the specification the AMBER staff assigned to the spectrograph. Simulations show that its total contribution to visibility loss of AMBER is less than 2%.
The paper describes the design of the single conjugate Adaptive Optics system to be installed on the LBT telescope. This system will be located in the Acquisition, Guiding and Wavefront sensor unit (AGW) mounted at the front bent Gregorian focus of LBT. Two innovative key features of this system are the Adaptive Secondary Mirror and the Pyramid Wavefront Sensor. The secondary provides 672 actuators wavefront correction available at the various foci of LBT. Due to the adaptive secondary mirror there is no need to optically conjugate the pupil on the deformable mirror. This allows having a very short sensor optical path made up using small dimension refractive optics. The overall AO system has a transmission of 70 % and fits in a rectangle of about 400×320mm. The pyramid sensor allows having different pupil sampling using on-chip binning of the detector. Main pupil samplings for the LBT system are 30×30, 15×15 and 10×10. Reference star acquisition is obtained moving the wavefront sensor unit in a field of view of 3×2 arcmin. Computer simulations of the overall system performance show the good correction achievable in J, H, and K. In particular, in our configuration, the limiting magnitude of pyramid sensor results more than one magnitude fainter with respect to Shack- Hartmann sensor. This feature directly translates in an increased sky coverage that is, in K band, about doubled with respect to the same AO system using a Shack-Hartmann sensor.
The latest generation of astronomical telescopes is equipped by primary mirrors about 8 meter in diameter increasing demands not only of the general mechanical structure but also of the technical performances of the mirror support systems. The Large Binocular Telescope has two 8.4 meter primary mirrors supported on the same elevation mechanical structure and, each of them, located in a mirror cell enviroment. Into the latter structures hundredth of pneumatic actuators bear the weigth of the primary mirror and six positioning actuators find out the six degrees of freedom of the mirror itself, then a new control system is able to determine realtime the stiffness and the damping required by the primary mirror system. In this paper the authors describe the mechanical and the electronic active control system design and testing of the position actuator prototype that mechanically link the 8.4 m honeycomb mirror to six rigidly reinforced locations on each primary Mirror Cell structure. During telescope operation, the adjustable length of the actuators precisely control the six degrees of freedom of the mirror. Each actuator has a high mechanical axial stiffness and, as new feature, an active control system, based on piezoelectric elements and capacitive sensor, in order to control the axial stiffness versus damping, with a bandwidth from DC up to 50 Hz, assuring that the natural frequencies of the mirror do not degrade the optical performance of the telescope under external forces as the wind spectrum. Moreover, other requirements have been satisfied in the mechanic of the actuators: flexures are provided to minimize any moments applied to the attachment of the actuator to the mirror; one axial load cell for each actuator provides a precise realtime measurement of the external forces applied to the mirror, such as wind loads, to feedback the pneumatic force system that supports the weight of the mirror; a very sensitive and precise capacitive sensor measures the total length of the actuator to submicron resolution upon request. Last but not least each actuator has a reliable fail-safe system that limits the compressive and tensile forces that can be applied to the mirror. The mechanical and the electronic design DSP based and all the experimental tests of this actuator prototype have been performed in the Astrophysical Observatory of Arcetri laboratories under the supervision of the authors of this paper.