The second generation of ELT instruments includes an optical-infrared high-resolution spectrograph, ANDES, ArmazoNes high Dispersion Echelle Spectrograph. It covers a wide spectral range that goes from 0.4 to 1.8μm (goal 0.35 to 2.4μm). A common model of detector is planned for the two visible spectrographs RIZ and UBV. A total of five detectors will cover the latter spectral range. A common detector unit design has been developed based on ELT's standard components and inspired by the previous successful detector units designed for HARPS and ESPRESSO. It consists of a 9k x 9k CCD detector, a differential vacuum cryostat that keeps the detector in its dedicated vacuum chamber and a cryocooler that cools down the detector to minimize the dark noise. The required temperature, mechanical and pressure stabilities drive the design of the detector unit.
The ESO/ELT ANDES (ArmazoNes high Dispersion Echelle Spectrograph) project successfully completed the system architecture review and is currently finalizing its preliminary design phase. ANDES is the high-resolution spectrograph for the ELT (ESO Extremely Large Telescope) capable of reaching a resolution of R ~ 100,000 simultaneously, in a wavelength range between 0.35 -2.4 µm (goals included), characterized by high-precision and extreme calibration accuracy suitable to address a variety of flagship scientific cases across a wide range of astronomical domains. To fulfill the required specifications the proposed design adopts a modular approach where the instrument is split in four individual spectrographs, each fiber-fed, and thermally and vacuum stabilized. A dedicated front-end which host a single conjugated adaptive optics module, collects either the light from the telescope or from a calibration unit feeding in turn the individual spectrographs. To master the described complexity the same modularity is reflected also at the project management level: each of the 9 subsystems (counting also the software as a standalone subsystem) is under direct responsibility of different teams coordinated by the ANDES project office. The high distribution and the large community involvement, consisting of 24 institutes from 13 countries, represent certainly a challenge from the project management point of view. In this paper we present the project management approach we envisaged to master successfully all the ANDES project phases from the finalization of the preliminary design up to commissioning on-sky; in particular we will describe in detail the risk management and PA/QA activities we have foreseen to assure appropriate risk mitigation and an overall high-quality standard required for the ANDES project.
4MOST is a new high-multiplex, wide-field spectroscopic survey facility under construction for ESO's 4m-VISTA telescope at Paranal, Chile. Its key specifications are: a large field of view of 4.4 square degrees, a high multiplex fibre positioner based on the tilting spine principle positioning 2436 science fibres, 1624 fibres going to two low-resolution spectrographs (R = λ/Δλ ~ 6500), and 812 fibres transferring light to the high-resolution spectrograph (R ~ 20,000). The instrument is entirely completed and is being shipped to Paranal Observatory, Chile in the first few months of 2024. Commissioning will take place summer 2024 with full operations expected to start early 2025. An overview will be given of instrument capabilities, the planned, and the unique operational scheme of 4MOST.
MOSAIC is the Multi-Object Spectrograph (MOS) for the 39m Extremely Large Telescope (ELT) of the European Southern Observatory (ESO), with unique capabilities in terms of multiplex, wavelength coverage and spectral resolution. It is a versatile multi-object spectrograph working in both the Visible and NIR domains, designed to cover the largest possible area (∼40 arcmin2) on the focal plane, and optimized to achieve the best possible signal-to-noise ratio on the faintest sources, from stars in our Galaxy to galaxies at the epoch of the reionization. In this paper we describe the main characteristics of the instrument, including its expected performance in the different observing modes. The status of the project will be briefly presented, together with the positioning of the instrument in the landscape of the ELT instrumentation. We also review the main expected scientific contributions of MOSAIC, focusing on the synergies between this instrument and other major ground-based and space facilities.
We present here the preliminary design of the RIZ module, one of the visible spectrographs of the ANDES instrument. It is a fiber-fed high-resolution, high-stability spectrograph. Its design follows the guidelines of successful predecessors such as HARPS and ESPRESSO. In this paper we present the status of the spectrograph at the preliminary design stage. The spectrograph will be a warm, vacuum-operated, thermally controlled and fiber-fed echelle spectrograph. Following the phase A design, the huge etendue of the telescope will be reformed in the instrument with a long slit made of smaller fibers. We discuss the system design of the spectrographs system.
The first generation of ELT instruments includes an optical-infrared high resolution spectrograph, indicated as ELT-HIRES and recently christened ANDES (ArmazoNes high Dispersion Echelle Spectrograph). ANDES consists of three fibre-fed spectrographs ([U]BV, RIZ, YJH) providing a spectral resolution of ∼100,000 with a minimum simultaneous wavelength coverage of 0.4-1.8 μm with the goal of extending it to 0.35-2.4 μm with the addition of an U arm to the BV spectrograph and a separate K band spectrograph. It operates both in seeing- and diffraction-limited conditions and the fibre-feeding allows several, interchangeable observing modes including a single conjugated adaptive optics module and a small diffraction-limited integral field unit in the NIR. Modularity and fibre-feeding allows ANDES to be placed partly on the ELT Nasmyth platform and partly in the Coudé room. ANDES has a wide range of groundbreaking science cases spanning nearly all areas of research in astrophysics and even fundamental physics. Among the top science cases there are the detection of biosignatures from exoplanet atmospheres, finding the fingerprints of the first generation of stars, tests on the stability of Nature’s fundamental couplings, and the direct detection of the cosmic acceleration. The ANDES project is carried forward by a large international consortium, composed of 35 Institutes from 13 countries, forming a team of almost 300 scientists and engineers which include the majority of the scientific and technical expertise in the field that can be found in ESO member states.
We present the design of the ANDES UBV module, the bluest spectrograph of the ANDES instrument. It is a fiber-fed high resolution, high stability spectrograph, which will be installed on the ELT-Nasmyth platform to minimize blue fibre losses from the focal plane to the spectrograph. In this paper we present the status of development of the spectrograph, its optical design, and auxiliary devices like exposure meter and leveling system, at the preliminary design stage. As stability is the prime design driver, a thermal enclosure is provided to keep temperature of the optical train stable at ambient conditions, and the pressure is kept constant at high vacuum level. The science, sky background and simultaneous calibration light is fed to the spectrographs via fiber bundles of 66 fibres, which are arranged in a straight row forming the spectrograph slit.
4MOST is a versatile spectroscopic facility soon to be installed on the ESO VISTA Telescope at Paranal. Prior to shipment to Chile, our team is conducting a comprehensive characterization of the instrument in a controlled laboratory setting. This preparatory phase is crucial for ensuring the fulfilment of both technical specifications and some key user requirements. The goal of this verification campaign is to obtain characterization data which will benchmark the performance of the spectrographs and the calibration unit against established metrics. The data primarily tests the spectral performance of the three spectrographs, the stability of the system, including the calibration unit, as well as the fiber throughput, which are pivotal for the success of 4MOST’s ambitious science goals. Additionally, the verification contains a selection of user requirements, ensuring the instrument’s readiness for the diverse scientific objectives it aims to enable. The results from these tests inform the observational strategy for future normal science operations. In this paper we outline the undertaken preparatory work, the applied testing procedures, and the anticipated implications of these tests, and their results, in the context of the final verification at the telescope, commissioning and normal science operations. This initial test phase marks a critical juncture in the 4MOST project timeline, setting the stage for a successful commissioning.
The RIZ & UBV visible spectrographs of the ANDES instrument, which are foreseen to be installed at the Extremely Large Telescope, require to be under a very stable high vacuum and at an extremely stable temperature of 1mK to reach the radial velocity goal of 10cm/s RMS over a 10-year period. The baseline design, integration and first analyses of the 5.5t aluminum vacuum tank, vacuum system, and the thermal enclosure of the two-room temperature spectrographs are presented in this paper. A very analogous configuration is proposed for both instruments in view of their similarities. In addition, this article addresses the finite rigidity of the Nasmyth platform and its consequences on the instrument design together with a potential collaborative multi-CAD Product Design Management platform description.
KEYWORDS: Lenses, Telescopes, Astronomical imaging, Optical alignment, Spectroscopy, Analog to digital converters, Field spectroscopy, Tolerancing, Equipment, Assembly tolerances
The 4-metre multi-object spectroscopic telescope (4MOST) is a fiber-fed multi-object spectrograph for the VISTA telescope at the European Southern Observatory (ESO) Paranal Observatory in Chile. The goal of the 4MOST project is to create a general purpose and highly efficient spectroscopic survey facility for astronomers in the 4MOST consortium and the ESO community. The instrument itself will record 2436 simultaneous spectra over a ∼4.2 square deg field of view and consists of an optical wide-field corrector (WFC), a fiber positioner system based on a tilting spine design, and three spectrographs giving both high and low spectral dispersion. The WFC comprises of six lenses grouped into four elements, two of which are cemented doublets that act as an atmospheric dispersion corrector. The first lens element is 0.9 m in diameter while the diameter of the other elements is 0.65 m. For the instrument to meet its science goals, each lens was aligned to be well within ∼100 μm—a major challenge. This was achieved using contact metrology methods supplemented by pencil beam laser probes. In particular, an off-axis laser beam system has been implemented to test the optics’ alignment before and after shipment. This work details the alignment and assembly methods and presents the latest results on the achieved lens positioning and projected performance of the WFC.
4MOST is a wide-field, high-multiplex, fibre-fed spectrograph, which will be mounted on the ESO VISTA telescope. High- and low-redshift surveys, targeting stars, galaxies, and AGN, can be executed in parallel, populating all the available 2436 fibers. Here, we present the 4MOST calibration plan, concentrating on the unique features dictated by the design of the instrument. These include the night-time backillumination of the fibers for precise metrology, simultaneous calibrations by dedicated fibers, attached night-time flatfield and wavelength calibration via a laser driven light source with a Fabry Perot etalon (FPE) on a moving carriage, and the observations of benchmark, telluric, and radial velocity standards for the science cross-calibration between 4MOST and complementary surveys from other telescopes.
The first generation of ELT instruments includes an optical-infrared high resolution spectrograph, indicated as ELT-HIRES and recently christened ANDES (ArmazoNes high Dispersion Echelle Spectrograph). ANDES consists of three fibre-fed spectrographs (UBV, RIZ, YJH) providing a spectral resolution of ∼100,000 with a minimum simultaneous wavelength coverage of 0.4-1.8 µm with the goal of extending it to 0.35-2.4 µm with the addition of a K band spectrograph. It operates both in seeing- and diffraction-limited conditions and the fibre-feeding allows several, interchangeable observing modes including a single conjugated adaptive optics module and a small diffraction-limited integral field unit in the NIR. Its modularity will ensure that ANDES can be placed entirely on the ELT Nasmyth platform, if enough mass and volume is available, or partly in the Coudé room. ANDES has a wide range of groundbreaking science cases spanning nearly all areas of research in astrophysics and even fundamental physics. Among the top science cases there are the detection of biosignatures from exoplanet atmospheres, finding the fingerprints of the first generation of stars, tests on the stability of Nature’s fundamental couplings, and the direct detection of the cosmic acceleration. The ANDES project is carried forward by a large international consortium, composed of 35 Institutes from 13 countries, forming a team of more than 200 scientists and engineers which represent the majority of the scientific and technical expertise in the field among ESO member states.
The Calibration Unit for 4MOST is providing hundreds of highly stable sharp spectral features with high power and mimicking the sky over the focal plane. The heart of the system is a combination of a bright broadband lamp and a Fabry-Perot etalon that provides a regular comb of spectral lines. 120 integrating spheres are distributed in 4 Light sabre linear arrays. These Light sabres are attached to the telescope spider struts and provide unvignetted illumination to the telescope focal plane. We describe the final design, the alignment, and the results of the testing.
The 4-metre Multi-Object Spectroscopic Telescope (4MOST) is a fibre-fed multi-object spectrograph for the VISTA telescope at the ESO Paranal Observatory in Chile. The goal of the 4MOST project is to create a general-purpose and highly efficient spectroscopic survey facility for astronomers in the 4MOST consortium and the ESO community. The instrument itself will record 2436 simultaneous spectra over a ∼4.2 square degree field of view and consists of an optical Wide-Field Corrector (WFC), a fibre positioner system based on a tilting spine design, and three spectrographs giving both high and low spectral dispersion. The WFC comprises of 6 lenses grouped into 4 elements, 2 of which are cemented doublets that act as an atmospheric dispersion corrector (ADC). The first lens element is 0.9m in diameter whilst the diameter of the other elements is 0.65m. For the instrument to meet its science goals, each lens needs to be aligned to ∼50µm – a major challenge. This is achieved using contact metrology methods supplemented by pencil beam laser probes. In particular, a novel off-axis laser beam system has been implemented to test the optics’ alignment before and after shipment. This paper details the alignment and assembly methods and presents the latest results on the achieved lens positioning and projected performance of the WFC
4MOST is a new high-multiplex, wide-field spectroscopic survey facility under construction for ESO's 4m-VISTA telescope at Paranal, Chile. Its key specifications are: a large field of view of 4.4 square degrees, a high multiplex fibre positioner based on the tilting spine principle that positions 2436 science fibres in the focal surface of which 1624 fibres go to two low-resolution optical spectrographs (R = λ/Δλ ~ 6500) and 812 fibres transfer light to the high-resolution optical spectrograph (R ~ 20,000). Currently, almost all subsystems are completed and full testing in Europe will be finished in spring 2023, after which 4MOST will be shipped to Chile. An overview is given of instrument construction and capabilities, the planned science of the consortium and the recently selected community programmes, and the unique operational scheme of 4MOST.
MOSAIC is the Multi-Object Spectrograph for the ESO Extremely Large Telescope, approved to enter Phase B beginning 2022. It is conceived as a multi- purpose instrument covering the Visible and Near Infrared bandwidth (0.45 –1.8 μm) with two observing modes: spatially resolved spectroscopy with 8 integral field units; and the simultaneous observation of 200 objects in the VIS and NIR in unresolved spectroscopy.
We present an overview of the main MOSAIC science drivers and the actual baseline design for the instrument. The prototyping and developments undertaken by the consortium to evaluate the feasibility of the project are also discussed.
The implementation of the 4MOST Facility at the ESO Paranal 4-meter VISTA wide-field telescope requires a substantial modification of the telescope. Since the current acquisition and guiding (A&G) and wavefront sensing optical systems (WFS) are embedded in VIRCAM and will be removed with it, replacements had to be provided. Although the A&G and WFS cameras will serve different purposes, they share common requirements. Among the shared requirements, a few are particularly challenging. For example, the environmental conditions the cameras will be exposed to require them to have an IP54 protection and due to their location, they cannot dissipate heat to the ambient air. To ensure optical alignment, the cameras must have very accurate housing and mechanical interfaces. In addition, both have to be integrated into an existing telescope control environment, with all that this entails in terms of service interfaces and protocols that can be used (e.g. GigE Vision), as well as operational requirements that must be met. After considering the specific performance requirements for the A&G cameras, the WFS detectors and the secondary guider sensor, a decision was made to use the same custom designed CCD camera model for all of them. These cameras are provided by Spectral Instruments. In this work we present the requirements for such cameras, their opto-mechanical design and the first results of their verification campaign, both at Spectral Instrument and AIP premises.
At the end of 2021, the ESO council approved the start of the construction phase for a High Resolution Spectrograph for the ELT, formerly known as ELT-HIRES, renamed recently as ANDES (ArmazoNes high Dispersion Echelle Spectrograph). The current initial schedule foresees a 9-years development aimed to bring the instrument on-sky soon after the first-generation ELT instruments. ANDES combines high spectral resolution (up to 100,000), wide spectral range (0.4 µm to 1.8 µm with a goal from 0.35 µm to 2.4 µm) and extreme stability in wavelength calibration accuracy (better than 0.02 m/s rms over a 10-year period in a selected wavelength range) with massive optical collecting power of the ELT thus enabling to achieve possible breakthrough groundbreaking scientific discoveries. The main science cases cover a possible detection of life signatures in exoplanets, the study of the stability of Nature’s physical constants along the universe lifetime and a first direct measurement of the cosmic acceleration. The reference design of this instrument in its extended version (with goals included) foresees 4 spectrographic modules fed by fibers, operating in seeing and diffraction limited (adaptive optics assisted) mode carried out by an international consortium composed by 24 institutes from 13 countries which poses big challenges in several areas. In this paper we will describe the approach we intend to pursue to master management and system engineering aspects of this challenging instrument focused mainly on the preliminary design phase, but looking also ahead towards its final construction.
The 4-meter Multi-Object Spectroscopic Telescope (4MOST) is a wide-field, high-multiplex spectroscopic survey facility under development for the Visible and Infrared Survey Telescope for Astronomy (VISTA) of the European Southern Observatory (ESO). The 4MOST Wide Field Corrector and Atmospheric Dispersion Corrector (ADC) lenses have been manufactured and tested at KiwiStar Optics, New Zealand. The two ADC wedged doublets form a Risley Prism Pair; are both 650 mm in diameter and relatively thin; and have been cemented using Sylgard 184 silicone elastomer. The cementing procedure and its challenges are reported here. Interferometric measurements of the single surfaces, glass blanks and the finished doublets have been compared in order to assess the effect of the cementing process on the final surface figures of the doublets before and after positioning in their cells.
A status overview of 4MOST is presented, a new high-multiplex, wide-field spectroscopic survey facility under construction for ESO's VISTA telescope at Paranal. Its key specifications are: a large field of view of 4.4 deg2 and a high multiplex capability, with 1624 fibres feeding two low-resolution spectrographs (R = λ/Δλ ~ 6500), and 812 fibres transferring light to the high-resolution spectrograph (R ~ 20 000). The 4MOST system integration has commenced and the selection process for ESO community survey programmes has been started. This overview presents the expected performance of the instrument, the science the consortium expects to carry out, and the unique operational scheme of 4MOST.
A novel concept for the calibration of multi object fiber-fed spectrographs is described for the 4MOST instrument. The 4MOST facility is foreseen to start science operations in 2022 at the ESO VISTA telescope. The calibration system provides intensity, wavelength and resolution calibrations for the 4MOST spectrographs. The heart of the system is a combination of a bright broad band lamp and a Fabry-Perot etalon. The lamp is able to provide sufficient flux to illuminate the VISTA focal plane and the Fabry-Perot etalon provides a regular comb of spectral lines. The Fabry-Perot etalon can be moved in and out of the optical beam to choose between intensity and spectral calibrations. A fiber bundle of 156 fibers is guided to the VISTA spider arms where each fiber is connected to a small integrating sphere. The integrating spheres are attached to the bottom side of the four VISTA telescope spider struts and provide unvignetted illumination of the telescope. The exit port of the integrating spheres is projected on the VISTA focal plane with a small collimator lens. The integrating spheres assure a uniform illumination of the focal plane and are insensitive to FRD effects of the input fibers due to motion and stress during telescope movements. The calibration system illumination only originates from the telescope spiders and therefore the telescope pupil is not fully filled. The calibration system uses the azimuthal scrambling properties of the fibers that connect the telescope focal plane and the spectrometers to completely fill the spectrograph pupil.
With more than 200 scientists and engineers involved, the design and manufacture of the 4MOST instrument, a secondgeneration spectroscopic instrument built for ESO's 4.1-metre VISTA telescope, is a challenge requiring the implementation of an efficient quality assurance strategy during each project phase (i.e., design, manufacture, test, installation, and operation), and including the maintenance. This paper introduces the 4MOST product assurance approach used by the project to make sure that 4MOST will comply with all necessary quality and safety requirements over the whole instrument’s lifetime of 15 years. For quality assurance, the guiding principles are mainly given by the ISO 10007:2017 and ISO 9001:2015 quality management standards. Related to safety, 4MOST design and manufacture complies not only with the essential safety requirements from the European Union New Approach Directives (CE Marking Directives), but also with the additional requirements coming from the ESO Safety Policy, issued by the ESO Management for ESO-wide application. The implementation of the 4MOST project’s Quality Assurance and Configuration Management is described in detail in the paper.
We present an overview and status update of the 4MOST project at the Final Design Review. 4MOST is a major new wide-field, high-multiplex spectroscopic survey facility under development for the VISTA telescope at the Paranal Observatory of ESO. Starting in 2022, 4MOST will deploy 2436 optical fibres in a 4.1 square degree field-of-view using a fibre positioner based on the tilting spine principle. The fibres will feed one high-resolution (R~20,000) and two low-resolution (R~5000) spectrographs that all have fixed configuration, 3-channel designs with identical 6k x 6k CCD detectors. Updated performance estimates will be presented based on components already manufactured and pre-production prototypes of critical subsystems.
The 4MOST science goals are mostly driven by a number of large area, space-based observatories of prime European interest: Gaia and PLATO (Galactic Archeology and Stellar Physics), eROSITA (High-Energy Sky), and Euclid (Cosmology and Galaxy Evolution). Science cases based on these observatories, along with wide-area ground-based facilities such as LSST, VISTA and VST drive the ten Consortium Surveys covering a large fraction of the Southern sky, with bright time mostly devoted to the Milky Way disk and bulge areas and the Magellanic Clouds, and the dark/gray time largely devoted to extra-galactic targets. In addition there will be a significant fraction of the fibre-hours devoted to Community Surveys, making 4MOST a true general-purpose survey facility, capable of delivering spectra of samples of objects that are spread over a large fraction of the sky.
The 4MOST Facility Simulator was created to show the feasibility of the innovative operations scheme of 4MOST with all surveys operating in parallel. The simulator uses the mock catalogues created by the science teams, simulates the spectral throughput and detection of the objects, assigns the fibres at each telescope pointing, creates pointing distributions across the sky and simulates a 5-year survey (including overhead, calibration and weather losses), and finally does data quality analyses and computes the science Figure-of-Merits to assess the quality of science produced. The simulations prove the full feasibility of running different surveys in parallel.
The 4MOST Facility is a high-multiplex, wide-field, brief-fed spectrograph system for the ESO VISTA telescope. It aims to create a world-class spectroscopic survey facility unique in its combination of wide-field multiplex, spectral resolution, spectral coverage, and sensitivity. At the end of 2014, after a successful concept optimization design phase, 4MOST entered into its Preliminary Design Phase. Here we present the process and tools adopted during the Preliminary Design Phase to define the subsystems specifications, coordinate the interface control documents and draft the system verification procedures.
We present an overview of the 4MOST project at the Preliminary Design Review. 4MOST is a major new wide-field, high-multiplex spectroscopic survey facility under development for the VISTA telescope of ESO. 4MOST has a broad range of science goals ranging from Galactic Archaeology and stellar physics to the high-energy physics, galaxy evolution, and cosmology. Starting in 2021, 4MOST will deploy 2436 fibres in a 4.1 square degree field-of-view using a positioner based on the tilting spine principle. The fibres will feed one high-resolution (R~20,000) and two medium resolution (R~5000) spectrographs with fixed 3-channel designs and identical 6k x 6k CCD detectors. 4MOST will have a 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. The 4MOST Facility Simulator (4FS) was developed to demonstrate the feasibility of this observing concept, showing that we can expect to observe more than 25 million objects in each 5-year survey period and will eventually be used to plan and conduct the actual survey.
For the LBT Observatory, the next couple of years promise to be both exciting and challenging. Exciting as the long awaited suite of first generation instruments and GLAO become available for binocular operations, while regular interferometric observations will make LBT the first operational ELT. Challenging because LBTO will have to handle maintenance and upgrades of instruments or key components like its adaptive secondaries about which it has much to learn. Step1 will outline a plan optimizing LBTOs scientific production while mitigating the consequences of the inevitable setbacks the challenges will bring.
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].
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.
ARGOS is the Laser Guide Star and Wavefront sensing facility for the Large Binocular Telescope. With first laser light on sky in 2013, the system is currently undergoing commissioning at the telescope. We present the overall status and design, as well as first results on sky. Aiming for a wide field ground layer correction, ARGOS is designed as a multi- Rayleigh beacon adaptive optics system. A total of six powerful pulsed lasers are creating the laser guide stars in constellations above each of the LBTs primary mirrors. With a range gated detection in the wavefront sensors, and the adaptive correction by the deformable secondary’s, we expect ARGOS to enhance the image quality over a large range of seeing conditions. With the two wide field imaging and spectroscopic instruments LUCI1 and LUCI2 as receivers, a wide range of scientific programs will benefit from ARGOS. With an increased resolution, higher encircled energy, both imaging and MOS spectroscopy will be boosted in signal to noise by a large amount. Apart from the wide field correction ARGOS delivers in its ground layer mode, we already foresee the implementation of a hybrid Sodium with Rayleigh beacon combination for a diffraction limited AO performance.
KEYWORDS: Information technology, Software development, Observatories, Telescopes, Adaptive optics, Efficient operations, Switches, Prototyping, Lab on a chip, Control systems
The LBTO software and IT group was originally responsible for development of the Telescope Control System (TCS) software, and build-out of observatory Information Technology (IT) infrastructure. With major construction phases of the observatory mostly completed, emphasis is transitioning toward instrument software handover support, IT infrastructure obsolescence upgrades, and software development in support of efficient operations. This paper discusses recent software and IT group activities, metrics, issues, some lessons learned, and a near-term development road-map for support of efficient operations.
The Large Binocular Telescope Observatory is a collaboration between institutions in Arizona, Germany, Italy, Indiana, Minnesota, Ohio and Virginia. The telescope uses two 8.4-m diameter primary mirrors mounted sideby- side on the same AZ-EL mount to produce a collecting area equivalent to an 11.8-meter aperture. Many science observations collect the light from the two sides separately. With the arrival of the second copy of the near-infrared spectrometer and the second copy of the optical spectrometer, the telescope is observing with both apertures a significant fraction of the time. The light from the two primary mirrors can be combined to produce phased-array imaging of an extended field. This coherent imaging along with adaptive optics gives the telescope the diffraction-limited resolution of a 22.65-meter telescope. Adaptive optics loops are routinely closed with natural stars on both sides of the telescope for combined beam observations. Twin laser guide star constellations have recently been installed for ground layer adaptive optics observations. Commissioning of new instruments and focal stations for high resolution spectroscopy and near-infrared phased-array imaging is underway.
Commissioning of a telescope facility such as the Large Binocular Telescope presents us with unprecedented challenges.
The logistical and managerial balance act of scheduling commissioning of telescope, adaptive optics and twelve focal
stations with subsequent commissioning of the instruments that populate the focal stations, while still providing for
adequate science opportunity with already operational instruments is an equation that is problematic to solve in a way
that meets the interests of all stakeholders. This paper presents strategies and priorities applied at the LBTO, and status
of telescope commissioning programs. We provide a summary of telescope commissioning results, including a
discussion about specific efforts to improve performance of the LBT.
The Large Binocular Telescope (LBT) Observatory is a collaboration between institutions in Arizona, Germany,
Italy, Indiana, Minnesota, Ohio and Virginia. The telescope on Mt. Graham in southeastern Arizona uses two
8.4-meter diameter borosilicate honeycomb primary mirrors mounted side-by-side to produce a collecting area
equivalent to an 11.8-meter circular aperture. A unique feature of LBT is that the light from the two primary
mirrors can be combined to produce phased-array imaging of an extended field. This coherent imaging along with
adaptive optics gives the telescope the diffraction-limited resolution of a 22.65-meter telescope. The first on-sky
phasing of the two telescopes in the mid-infrared occurred in October 2010 with the LBTI instrument in Fizeau
mode. The telescope control system has been upgraded to allow binocular (2-sided) observations with pairs of
instruments. The prime focus cameras (LBC) routinely operate in this mode. Improved collimation and pointing
models have been deployed to keep both sides collimated and pointed at the same target. The control system
has also been upgraded to allow observations of solar system objects at non-sidereal tracking rates. Science
observations are scheduled for 60% of the nights including a significant fraction of adaptive optics imaging with
the first adaptive secondary mirror and the FLAO system with natural guide stars. MODS1, a nearUV-optical
spectrometer, has been added to the suite of science instruments along with LBC (visible imagers) and LUCI1
(near infrared spectrometer). LMIRcam (2-5 microns) and PISCES (1-2.5 microns) have been used for adaptive
optics imaging. The remaining nights are scheduled for telescope and instrument commissioning activities as new
instruments arrive. The second of the two F/15 adaptive secondary mirrors has been installed on the telescope
in Fall 2011 and has been commissioned on-sky in Spring 2012.
ARGOS the Advanced Rayleigh guided Ground layer adaptive Optics System for the LBT (Large Binocular Telescope)
is built by a German-Italian-American consortium. It will be a seeing reducer correcting the turbulence in the lower
atmosphere over a field of 2' radius. In such way we expect to improve the spatial resolution over the seeing of about a
factor of two and more and to increase the throughput for spectroscopy accordingly. In its initial implementation,
ARGOS will feed the two near-infrared spectrograph and imager - LUCI I and LUCI II.
The system consist of six Rayleigh lasers - three per eye of the LBT. The lasers are launched from the back of the
adaptive secondary mirror of the LBT. ARGOS has one wavefront sensor unit per primary mirror of the LBT, each of the
units with three Shack-Hartmann sensors, which are imaged on one detector.
In 2010 and 2011, we already mounted parts of the instrument at the telescope to provide an environment for the main
sub-systems. The commissioning of the instrument will start in 2012 in a staged approach. We will give an overview of
ARGOS and its goals and report about the status and new challenges we encountered during the building phase. Finally
we will give an outlook of the upcoming work, how we will operate it and further possibilities the system enables by
design.
LINC-NIRVANA will employ four wave front sensors to realize multi-conjugate correction on both arms of a Fizeau interferometer for LBT. Of these, one of the two ground-layer wave front sensors, together with its infrared test camera, comprise a stand-alone test platform for LINC-NIRVANA. Pathfinder is a testbed for full LINC-NIRVANA intended to identify potential interface problems early in the game, thus reducing both technical, and schedule, risk. Pathfinder will combine light from multiple guide stars, with a pyramid sensor dedicated to each star, to achieve ground-layer AO correction via an adaptive secondary: the 672-actuator thin shell at the LBT. The ability to achieve sky coverage by optically coadding light from multiple stars has been previously demonstrated; and the ability to achieve correction with an adaptive secondary has also been previously demonstrated. Pathfinder will be the first system at LBT to combine both of these capabilities.
Since reporting our progress at A04ELT2, we have advanced the project in three key areas: definition of specific goals for Pathfinder tests at LBT, more detail in the software design and planning, and calibration. We report on our progress and future plans in these three areas, and on the project overall.
As of July 2012, the Large Binocular Telescope Observatory is supporting scientific observing 60% of the time with
binocular prime focus imaging, single-sided optical and near-IR imaging and spectroscopy, and adaptive optics imaging.
Interspersed in the last year were installation and commissioning of the second adaptive optics system and recommissioning
of the LUCI near-IR instrument with a replacement detector. Initial commissioning of mid-IR
interferometry is underway as well. We examine the lost time statistics and distribution of issues that reduced on-sky
access in the context of the limited technical support provided for observing. We discuss some of the root causes of and
responses to a critical operational readiness review. The manner in which programs are selected and scheduled for the
different partners is reviewed. The goal is to apply the lessons learned to the continuing period of observation plus
commissioning anticipated as new spectroscopic, adaptive optics, and interferometric capabilities are added through
2015.
By June 2010, the Large Binocular Telescope Observatory will have supported six semesters of observing with prime
focus imaging, with the addition of IR imaging and spectroscopy in the most recent. Interspersed in the last year were
installation and commissioning of one direct and one bent Gregorian focal station and extended commissioning of the
first bent Gregorian focal station. We examine the lost time statistics and distribution of issues that reduced on-sky
access in the context of the limited technical support provided for observing. We also note some of the restrictions
imposed by the alternation of engineering and commissioning activities with scheduled observing time. The goal is to
apply the lessons learned to the continuing period of observation plus commissioning anticipated as new spectroscopic,
adaptive optics, and interferometric capabilities are added through 2012.
We present the results from the commisioning of the first three off-axis
Acquisition, Guiding and Wavefront Sensing Units on the Large Binocular
Telescope. In particular we report on the performance of the units with
respect to image quality, optical efficiency and scattered light.
We also present the procedure for calibrating the stage
coordinate system astrometrically to the focal plane coordinates of the
telescope as well as the positional performance of the system.
The first of a total of four units was mounted on the telescope in
October 2007 and in the mean time three units have been mounted on the
telescope. The units have been used for commisioning of the focal stations as well as for scientific observations since the end of 2008 with LUCIFER-I, the near-IR images and MOS spectrograph
While the ultimate proof of telescope performance is in the quality and amount of science it is able to produce,
commissioning results give a good and in-depth indication of how well a telescope facility actually performs, both in
terms of sub-system commissioning and on-sky commissioning. Results from LBT commissioning activities are
presented, along with lessons learned and a discussion of the challenges for future commissioning required to prepare the
LBT for true Binocular Operation and ultimately interferometric operations.
The Large Binocular Telescope (LBT) Observatory is a collaboration between institutions in Arizona, Germany,
Italy, Indiana, Minnesota, Ohio and Virginia. The telescope on Mt. Graham in Arizona uses two 8.4-meter
diameter primary mirrors mounted side-by-side to produce a collecting area equivalent to an 11.8-meter circular
aperture. A unique feature of LBT is that the light from the two primary mirrors can be combined to produce
phased-array imaging of an extended field. This cophased imaging along with adaptive optics gives the telescope
the diffraction-limited resolution of a 22.65-meter telescope. Binocular imaging with two co-pointed prime focus
cameras began in Fall 2007, and science observing continues routinely. We will describe the scientific results
and technical challenges of monocular Gregorian focus observations starting in Spring 2008. Commissioning of
the first Gregorian spectrometer (LUCIFER1) has been completed with a rigid secondary mirror, and science
observations have begun in December 2009. The telescope uses two F/15 adaptive secondaries to correct atmospheric
turbulence. The first of these adaptive mirrors has been tested in Italy with the adaptive loop closed, and
arrived at the telescope in February 2010. The first adaptive optics images were achieved on-sky in May 2010.
The Direct Gregorian focus has been prepared for the arrival of the second Gregorian spectrometer (MODS1).
ARGOS is the Laser Guide Star adaptive optics system for the Large Binocular Telescope. Aiming for a wide field
adaptive optics correction, ARGOS will equip both sides of LBT with a multi laser beacon system and corresponding
wavefront sensors, driving LBT's adaptive secondary mirrors. Utilizing high power pulsed green lasers the artificial
beacons are generated via Rayleigh scattering in earth's atmosphere. ARGOS will project a set of three guide stars above
each of LBT's mirrors in a wide constellation. The returning scattered light, sensitive particular to the turbulence close to
ground, is detected in a gated wavefront sensor system. Measuring and correcting the ground layers of the optical
distortions enables ARGOS to achieve a correction over a very wide field of view. Taking advantage of this wide field
correction, the science that can be done with the multi object spectrographs LUCIFER will be boosted by higher spatial
resolution and strongly enhanced flux for spectroscopy. Apart from the wide field correction ARGOS delivers in its
ground layer mode, we foresee a diffraction limited operation with a hybrid Sodium laser Rayleigh beacon combination.
Characterisation, mitigation and correction of telescope vibrations have proven to be crucial for the performance
of astronomical infrared interferometers. The project teams of the interferometers for the LBT, LINC-NIRVANA
and LBTI, and LBT Observatory (LBTO) have embarked on a joint effort to implement an accelerometer-based
vibration measurement system distributed over the optical elements of the LBT. OVMS, the Optical Path
Difference and Vibration Monitoring System will serve to (i) ensure conditions suitable for adaptive optics
(AO) and interferometric (IF) observations and (ii) utilize vibration information, converted into tip-tilt and
optical path difference data, in the control strategies of the LBT adaptive secondary mirrors and the beam
combining interferometers. The system hardware is mainly developed by Steward Observatory's LBTI team and
its installation at the LBT is underway. The OVMS software development and associated computer infrastructure
is the responsibility of the LINC-NIRVANA team at MPIA Heidelberg. Initially, the OVMS will fill a data archive
provided by LBTO that will be used to study vibration data and correlate them with telescope movements and
environmental parameters thereby identifiying sources of vibrations and to eliminate or mitigate them. Data
display tools will help LBTO staff to keep vibrations within predefined thresholds for quiet conditions for AO
and IF observations. Later-on real-time data from the OVMS will be fed into the control loops of the AO systems
and IF instruments in order to permit the correction of vibration signals with frequencies up to 450 Hz.
In this paper we present the laboratory characterization and performance evaluation of the First Light Adaptive
Optics (FLAO) the Natural Guide Star adaptive optics system for the Large Binocular Telescope (LBT). The
system uses an adaptive secondary mirror with 672 actuators and a pyramid wavefront sensor with adjustable
sampling of the telescope pupil from 30×30 down to 4×4 subapertures. The system was fully assembled in the
Arcetri Observatory laboratories, passing the acceptance test in December 2009. The performance measured
during the test were closed to goal specifications for all star magnitudes. In particular FLAO obtained 83%
Strehl Ratio (SR) in the bright end (8.5 magnitudes star in R band) using H band filter and correcting 495
modes with 30×30 subapertures sampling. In the faint end (16.4 magnitude) a 5.0% SR correcting 36 modes
with 7×7 subapertures was measured. The seeing conditions for these tests were 0.8" (r0 = 0.14m @ 550 nm)
and an average wind speed of 15m/s. The results at other seeing conditions up to 1.5" are also presented. The
system has been shipped to the LBT site, and the commissioning is taking place since March to December 2010.
A few on sky results are presented.
The Large Binocular Telescope (LBT) is built around two lightweight borosilicate honeycomb mirrors which, at
8.4 meters in diameter, are the largest operational examples of this technology. Since the mirrors are relatively
stiff, the LBT mirror support system relies on passive position control and active force control. Passive position
control is performed by six extendable hardpoints organized as a truncated hexapod, which may be positioned
as required by the active optics control loop. The hardpoints rely on their axial stiffness to maintain the mirror
position against residual external disturbances. The active force control system minimizes the force exerted by
the hardpoints on the glass. Additionally, the axial component of the nominally uniform active support forces
can be perturbed to distort the mirror as required by the active optics control loop. Because of the relatively
large CTE of borosilicate glass, the differential temperature of the mirror is critical. Thus, the force control
system must support a 16 metric ton mirror using less than 100 Watts of electrical power. The authors present
a description of the primary mirror support system as implemented at the LBT. Initial stability problems made
the mirrors nearly unusable in freezing temperatures. The authors explain the reason for this instability and
describe the solutions implemented. Data demonstrating the current performance of the primary mirror support
system are also presented.
KEYWORDS: Computer programming, Digital signal processing, Telescopes, Calibration, Electronics, Signal processing, Tolerancing, Analog electronics, Control systems, Demodulation
A typical high-resolution encoder interpolator relies on careful mechanical alignment of the encoder read-heads
and tight electrical tolerances of the signal processing electronics to ensure linearity. As the interpolation factor
increases, maintaining these tight mechanical and electrical tolerances becomes impractical. The Large Binocular
Telescope (LBT) is designed to utilize strip-type encoders on the main axes. Because of the very large scale of
the telescope, the accumulative length of the azimuth and elevation encoder strips exceeds 80 meters, making
optical tape prohibitively expensive. Consequently, the designers of the LBT incorporated the far less expensive
Farrand Controls Inductosyn® linear strip encoder to encode the positions of the main axes and the instrument
rotators. Since the cycle pitch of these encoders is very large compared to that of optical strip encoders, the
interpolation factor must also be large in order to achieve the 0.005 arcsecond encoder resolution as specified.
The authors present a description of the innovative DSP-based hardware / software solution that adaptively
characterizes and removes common systematic cycle-to-cycle encoder interpolation errors. These errors can
be caused by mechanical misalignment, encoder manufacturing flaws, variations in electrical gain, signal offset
or cross-coupling of the encoder signals. Simulation data are presented to illustrate the performance of the
interpolation algorithm, and telemetry data are presented to demonstrate the actual performance of the LBT
main-axis encoder system.
By June 2008, The Large Binocular Telescope Observatory will have supported two full semesters of observing with
prime focus imaging. Interspersed were optical alignment and initiation of binocular mode for the prime focus, as well as
installation and initial commissioning of the first bent Gregorian focal station. We examine the lost time statistics and
distribution of issues that reduced on-sky access in the context of the limited technical support provided for observing.
We also note some of the restrictions imposed by the alternation of engineering and commissioning activities with
scheduled observing time. The goal is to apply the lessons learned to the continuing period of observation plus
commissioning anticipated as new spectroscopic, adaptive optics, and interferometric capabilities are added through
2010.
The Large Binocular Telescope (LBT) Observatory is a collaboration between institutions in Arizona, Germany,
Italy, Indiana, Minnesota, Ohio and Virginia. The telescope on Mt. Graham in Southeastern Arizona uses two
8.4-meter diameter primary mirrors mounted side-by-side to produce a collecting area equivalent to an 11.8-meter
circular aperture. A unique feature of LBT is that the light from the two primary mirrors can be combined to
produce phased array imaging of an extended field. This coherent imaging along with adaptive optics gives
the telescope the diffraction-limited resolution of a 22.65-meter telescope. We will describe the scientific results
and technical challenges of monocular prime focus imaging starting in Fall 2006. Binocular imaging with two
co-pointed prime focus cameras began in Fall 2007. Installation of a rigid (non-adaptive) secondary mirror
occurred in Spring 2008 in time for the arrival of the first Gregorian spectrometer. The telescope will use two
F/15 adaptive secondaries to correct atmospheric turbulence. The first of these adaptive mirrors is now being
tested in Italy, and is planned to be at the telescope by Summer 2009.
The Large Binocular Telescope (LBT) is an international collaboration, with partners from the United States, Italy, and
Germany. The telescope uses two 8.4-meter diameter primary mirrors to produce coherent images with the combined
light along with adaptive optics.
The correct functioning and optimum performance of the LBT is only achieved through a complex interplay of various
optical elements. Each of these elements has its individual vibration behaviour, and therefore it is necessary to
characterize the LBT as a distributed vibration system.
LINC-NIRVANA is a near-infrared image-plane beam combiner with advanced, multi-conjugated adaptive optics, and
one of the interferometric instruments for the Large Binocular Telescope (LBT). Its spectral range goes from 1.0 μm to
2.45 μm, therefore the requirements for the maximum optical path difference (OPD) are very tight (λ/10 ~ 100 nm). 1
During two dedicated campaigns, the vibrations introduced by various actuators were measured using different kinds of
sensors. The evaluation of the obtained data allows an estimation of the frequency and amplitude contributions of the
individual vibration sources.
Until the final state of the LBT is reached, further measurements are necessary to optimize and adapt the equipment and
also the investigated elements and configurations (measurement points and directions, number of sensors, etc.).
Laser guide star adaptive optics and interferometry are currently revolutionizing ground-based near-IR astronomy, as
demonstrated at various large telescopes. The Large Binocular Telescope from the beginning included adaptive optics in
the telescope design. With the deformable secondary mirrors and a suite of instruments taking advantage of the AO
capabilities, the LBT will play an important role in addressing major scientific questions. Extending from a natural guide
star based system, towards a laser guide stars will multiply the number of targets that can be observed. In this paper we
present the laser guide star and wavefront sensor program as currently being planned for the LBT. This program will
provide a multi Rayleigh guide star constellation for wide field ground layer correction taking advantage of the multi
object spectrograph and imager LUCIFER in a first step. The already foreseen upgrade path will deliver an on axis
diffraction limited mode with LGS AO based on tomography or additional sodium guide stars to even further enhance
the scientific use of the LBT including the interferometric capabilities.
The Large Binocular Telescope Observatory is expecting to support its first routine observing runs for partner astronomers by early 2007. When fully operational, the variety of observing modes will require a combination of skilled staff and prepared observers for full scientific productivity. The pair of 8.4-meter primaries can be operated as parallel channels to feed permanently mounted, paired wide-field direct imaging cameras, and optical and near-IR spectrographs. The two pairs of spectrographs support custom-drilled multi-object masks, with particular care required for the vacuum exchange in the near-IR system. Instruments with initially restricted user groups include a high-dispersion, stable fiber-fed echelle spectrograph and two beam-combining interferometers. The near-IR spectrograph and beam-combining instruments will depend on routine and reliable high performance from the adaptive optics system, based on the two 0.9-m adaptive secondary mirrors. We present preliminary plans for specialist staffing and scheduling modes for support of the science and deployment of instrumental modes by the partners.
KEYWORDS: Computer programming, Control systems, Digital signal processing, Telescopes, Mirrors, Field programmable gate arrays, Clocks, Photonic integrated circuits, Local area networks, Head
The Large Binocular Telescope (LBT) features dual 8.4 m diameter mirrors in a common elevation-over-azimuth mount. The LBT moves in elevation on two large crescent-shaped C-rings that are supported by radial hydrostatic bearing pads located near the four corners of the rectangular azimuth frame. The azimuth frame, in turn, is supported by four hydrostatic bearing pads and uses hydrodynamic roller bearings for centering. Each axis is gear driven by four large electric motors. In addition to precision optical motor encoders, each axis is equipped with Farrand Inductosyn strip encoders which yield 0.005 arcsecond resolution. The telescope weighs 580 metric tons and is designed to track with 0.03 arcsecond or better servo precision under wind speeds as high as 24 km/hr. Though the telescope is still under construction, the Mount Control System (MCS) has been routinely exercised to achieve First Light. The authors present a description of the unique, DSP-based synchronous architecture of the MCS and its capabilities.
The Large Binocular Telescope Observatory (LBT) encoded their elevation and azimuth axis with Farrand Inductosyn tape encoders. The authors present the unique design requirements to achieve high precision tracking and pointing. This paper describes the mechanical hardware used to meet these goals. The telescope elevation axis uses two tapes to encode 14m diameter tracks machined into the optical support structure. Each elevation tape is encoded with two custom read heads machined to fit the surfaces. The read heads are mounted on spring loaded flexures with rollers to insure consistent alignment of the heads to the tapes and to allow for radial run out. The azimuth is encoded with two tapes set end to end. Four custom read heads have been installed on similar flexures. The tape mounting hardware has been designed to maintain uniform and constant tension over the lifetime of the tape. We also describe the equipment and procedures used during installation to insure uniform tension of the tape in the track.
Layer Oriented represented in the last few years a new and promising aproach to solve the problems related to the limited field of view achieved by classical Adaptive Optics systems. It is basically a different approach to multi conjugate adaptive optics, in which pupil plane wavefront sensors (like the pyramid one) are conjugated to the same altitudes as the deformable mirrors. Each wavefront sensor is independently driving its conjugated deformable mirror thus simplifying strongly the complexity of the wavefront computers used to reconstruct the deformations and drive the mirror themselves, fact that can become very important in the case of extremely large telescopes where the complexity is a serious issue. The fact of using pupil plane wavefront sensors allow for optical co-addition of the light at the level of the detector thus increasing the SNR of the system and permitting the usage of faint stars, improving the efficiency of the wavefront sensor. Furthermore if coupled to the Pyramid wavefront sensor (because of its high sensitivity), this technique is actually peforming a very efficient usage of the light leading to the expectation that, even by using only natural guide stars, a good sky coverage can be achieved, above all in the case of giant telescopes. These are the main reasons for which in the last two years several projects decided to make MCAO systems based on the Layer Oriented technique. This is the case of MAD (an MCAO demonstrator that ESO is building with one wavefront sensing channel based on the Layer Oriented concept) and NIRVANA (an instrument for LBT). Few months ago we built and successfully tested a first prototype of a layer oriented wavefront sensor and experiments and demonstrations on the sky are foreseen even before the effective first light of the above mentioned instruments. The current situation of all these projects is presented, including the extensive laboratory testing and the on-going experiments on the sky.
SINFONI is an adaptive optics assisted near-infrared integral field spectrometer for the ESO VLT. The Adaptive OPtics Module (built by the ESO Adaptive Optics Group) is a 60-elements curvature-sensor based system, designed for operations with natural or sodium laser guide stars. The near-infrared integral field spectrometer SPIFFI (built by the Infrared Group of MPE) provides simultaneous spectroscopy of 32 x 32 spatial pixels, and a spectral resolving power of up to 3300. The adaptive optics module is in the phase of integration; the spectrometer is presented tested in the laboratory. We provide an overview of the project, with particular emphasis on the problems encountered in designing and building an adaptive optics assisted spectrometer.
CRIRES is a cryogenic, pre-dispersed, infrared echelle spectrograph designed to provide a resolving power of 105 between 1 and 5 μm at a Nasmyth focus of one of the 8m VLT telescopes. A curvature sensing adaptive optics sytem feed is used to minimize slit losses and a 4096x512 pixel mosaic of Aladdin arrays is being developed to maximixe the free spectral range covered in each order. Insertion of gas cells to measure high precision radial velocities is foreseen and the possibility of combining a Fresnel rhomb with a Wollaston prism for magnetic Doppler imaging is under study. Installation at the VLT is scheduled during the second half of 2004. Here we briefly recall the major design features of CRIRES and describe its current development status.
MACAO stands for Multi Application Curvature Adaptive Optics. A similar concept is applied to fulfill the need for wavefront correction for several VLT instruments. MACAO-VLTI is one of these built in 4 copies in order to equip the Coude focii of the ESO VLT's. The optical beams will then be corrected before interferometric recombination in the VLTI (Very Large Telescope Interferometer) laboratory. MACAO-VLTI uses a 60 elements bimorph mirror and curvature wavefront sensor. A custom made board processes the signals provided by the wavefront detectors, 60 Avalanche Photo-diodes, and transfer them to a commercial Power PC CPU board for Real Time Calculation. Mirrors Commands are sent to a High Voltage amplifier unit through an optical fiber link. The tip-tilt correction is done by a dedicated Tip-tilt mount holding the deformable mirror. The whole wavefront is located at the Coude focus. Software is developed in house and is ESO compatible. Expected performance is a Strehl ratio sligthly under 60% at 2.2 micron for bright reference sources (star V<10) and a limiting magnitude of 17.5 (Strehl ~0.1). The four systems will be installed in Paranal successively, the first one being planned for June 2003 and the last one for June 2004.
The European Southern Observatory (ESO) and the Max Planck Institut fur extraterrestrische Physik (MPE) are jointly developing SINFONI, an Adaptive Optics (AO) assisted Near Infrared Integral Field Spectrometer, which will be installed in the first quarter of 2004 at the Cassegrain focus of YEPUN (VLT UT4). The Adaptive Optics Module, a clone of MACAO, designed and built by ESO, is based on a 60 elements curvature system. It feeds the 3D spectrograph, SPIFFI, designed and built by MPE, with higher than 50% K band Strehl for bright (V<12) on-axis Natural Guide Stars (NGS) and less than 35 mas/hour image motion. The AO-Module will be the first curvature AO system operated in Laser Guide Star (LGS) mode, using a STRAP system for the tip/tilt sensing. The Strehl performance in the LGS mode is expected to be better than 30% in K band.
Multi-Conjugate Adaptive Optics (MCAO) is working on the principle to perform wide field of view atmospheric turbulence correction using many Guide Stars located in and/or surrounding the observed target. The vertical distribution of the atmospheric turbulence is reconstructed by observing several guide stars and the correction is applied by some deformable mirrors optically conjugated at different altitudes above the telescope.
The European Southern Observatory together with external research institutions is going to build a Multi-Conjugate Adaptive Optics Demonstrator (MAD) to perform wide field of view adaptive optics correction. The aim of MAD is to demonstrate on the sky the feasibility of the MCAO technique and to evaluate all the critical aspects in building such kind of instrument in the framework of both the 2nd generation VLT instrumentation and the 100-m telescope OWL.
In this paper we present the conceptual design of the MAD module that will be installed at one of the VLT unit telescope in Paranal to perform on-sky observations. MAD is based on a two deformable mirrors correction system and on two multi-reference wavefront sensors capable to observe simultaneously some pre-selected configurations of Natural Guide Stars. MAD is expected to correct up to 2 arcmin field of view in K band.
The European Southern Observatory is developing a medium order curvature adaptive optics system designed to be operable with minimal modification at any focus of the Very Large telescope (VLT). The first application of this AO system (MACAO) is to equip all four VLT Unit Telescope (UT) Coude foci with 60 element AO systems capable of delivering to the VLT Interferometer (VLTI) > 50% K band Strehl. The AO system being used by an interferometer is constrained to introduce minimal piston and operating as a sub-system of a large and complex instrument to have a robust architecture and simple operation. Installation of the first AO system is scheduled to begin first Quarter 2002 with completion of all four UTs by early 2004. Other applications of the MACAO system will be for use by the CRIRES and SPIFFI spectrographs.
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