For the ELT, a total of 931 M1 Segment Assemblies will be manufactured. These will be of 133 different types, 7 copies each, with different optical and mechanical properties. The manufacturing of the segment support, the glass blank and the polishing will be done by industrial partners. ESO will be responsible for the shipment of the Segment Assemblies to Chile, for the integration of the edge sensors and their electronics, and for the cleaning and coating. After performing several health- and quality-checks, the Segment Assemblies will be temporarily stored in the warehouse, before being installed at the telescope and eventually recoated around every 2 years. The telescopes and instruments for optical astronomy are usually prototypes, while a new approach is required to manage such a series production of crucial components, which differ in small but significant aspects. In this paper, we will present the processes we have developed to manage the series production of M1 Segment Assemblies for the ELT, starting from the reception of the Segment Assemblies in Chile, inspection, installation of sub-components, health-checks, storage, and installation at the telescope.
The construction of the ELT is now in full swing. This is true both for the construction of the Dome and Main Structure (DMS) in Chile, but also for all the other sub-systems manufactured by industrial partners in Europe. While the DMS is entirely managed by the industrial consortium, the shipment to Chile and the installation at the telescope of the other subsystems is mostly under the responsibility of ESO. The shipment of these components from Europe to Chile has started recently and will soon reach a level of ~10'000 components/month. All these components will need to be tracked during their shipment, incoming inspections will need to be performed, health-checks and integration with other components will need to be done. The components will then be stored temporarily at the warehouse, before being installed at the telescope. We will present the approach for the logistics, infrastructure, and the tools set up to manage the status and location of all these components and to keep the link to their associated latest documentation.
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.
In this paper we will give an overview of the status of the three instruments and one adaptive optics module that are currently under construction for the European Southern Observatory (ESO) Extremely Large Telescope (ELT). Currently three of those instruments are in the final design stages and the adaptive optics module, MAORY, is rapidly approaching its Preliminary Design Review (PDR). Funding for the laser tomographic module for HARMONI has been secured and that module is now included as part of that overall instrument project. The PDR phase of the instruments has strongly highlighted the ambitious nature of these and all 30-m class instrument projects. Scientifically, managerially and technically, the step up from the 8-m class is challenging. This paper will provide an introduction to all these instruments and will highlight some of the important developments required to realise them.
Following the arrival of MATISSE, the second-generation of VLTI instrumentation is now complete and was simultaneously enhanced by a major facility upgrade including the NAOMI Adaptive Optics on the Auxiliary Telescopes. On the Unit Telescopes, significant efforts were also made to improve the injection stability into VLTI instruments. On top of GRAVITY's own evolution, its fringe tracker is now being used to allow coherent integrations on MATISSE (the so-called GRA4MAT project). Meanwhile, operations also evolved to be more flexible and make the most of an extended observing parameter space. In this context, we present an overview of the current VLTI performances. Finally, we will report on on-going improvements such as the extension of the longest baselines.
This paper proposes the usage of IBM Rational DOORS for the planning, controlling and supporting the verification of a system. This includes defining the verification methods & stages for technical requirements, defining the verification activities, establishing links between technical requirements and verification activities, defining the scope and success criteria of tests, monitoring the progress of the verification campaigns and finally the generation of the compliance matrix, all within a single tool. We illustrate the usage of this tool over the entire lifecycle of two recent projects (NAOMI, 4MOST) and give an outlook of its application to the verification of the Extremely Large Telescope (ELT).
HARMONI is the adaptive optics assisted, near-infrared and visible light integral field spectrograph for the Extremely Large Telescope (ELT). A first light instrument, it provides the work-horse spectroscopic capability for the ELT. As the project approaches its Final Design Review milestone, the design of the instrument is being finalized, and the plans for assembly, integration and testing are being detailed. We present an overview of the instrument’s capabilities from a user perspective, provide a summary of the instrument’s design, including plans for operations and calibrations, and provide a brief glimpse of the predicted performance for a specific observing scenario. The paper also provides some details of the consortium composition and its evolution since the project commenced in 2015.
The ESO Extremely Large Telescope (ELT) has been in construction since 2014. In parallel with the construction of the telescope, ESO has entered into agreements with consortia in the ESO member states to build the first instruments for that telescope. To meet the telescope science goals, the ambitious instrument plan includes two instruments for first light: an optical to near-infrared integral field spectrograph with a dedicated adaptive optics system (HARMONI) and a near-infrared camera with simple spectrograph (MICADO) behind a multi-conjugate adaptive optics module (MAORY). The next instrument will be a mid-infrared imager and spectrograph (METIS). Plans to follow this first suite of instruments include a high-resolution spectrograph (HIRES) and a multi-object spectrograph (MOSAIC). Technology development is underway to prepare for building the ELT Planetary Camera and Spectrograph. An overview of the telescope and its instruments is given.
The Very Large Telescope Interferometer Auxiliary Telescopes will soon be equipped with an adaptive optics system called NAOMI. The corrective optics deformable mirror is the commercial DM241 from ALPAO. Being part of an interferometer operating from visible to mid-infrared, the DMs of NAOMI face several challenges (high level of reliability, open-loop chopping, piston-free control, WFS/DM pupil rotation, high desired bandwidth and stroke). We here describe our extensive characterization of the DMs through measurements and simulations. We summarize the operational scenario we have defined to handle the specific mirror properties. We conclude that the ALPAO DMs have overall excellent properties that fulfill most of the stringent requirements and that deviations from specifications are easily handled. To our knowledge, NAOMI will be the first astronomical system with a command in true Zernike modes (allowing software rotation), and the first astronomical system in which a chopping is performed with the deformable mirror (5” sky, at 5 Hz).
This paper aims to compare various aspects of systems engineering between space and ground-based astronomy projects. After a brief roundup of the development of systems engineering practices in space, we discuss the rapidly progressing adoption of similar methods in complex ground projects. Special attention is given to the analysis of increasing system complexity on ground which leads to a commensurate increase in project effort and cost. The importance of development of enabling technologies and improvement of engineering methodologies are discussed by specific examples.
This paper presents the plan for the system-level requirements verification of the ESO ELT. It describes the process to undertake this already ongoing activity and the tools supporting such process.
Verification methods (design, analysis, inspection and/or test), verification level (whether the concerned requirement is verified at system or subsystem level), milestones (at which stage in the programme the requirement is verified) and constraints, when applicable, are discussed. Particular emphasis is put on addressing how the key system requirements, i.e., the ones with a larger impact on the science return, are planned to be verified. Also, special attention is given to describe the model approach in place to help in the system-level verification activity.
Finally, some conclusions and lessons learned extracted so far from the system requirements verification activity are summarized.
The near-infrared GRAVITY instrument has become a fully operational spectro-imager, while expanding its capability to support astrometry of the key Galactic Centre science. The mid-infrared MATISSE instrument has just arrived on Paranal and is starting its commissioning phase. NAOMI, the new adaptive optics for the Auxiliary Telescopes, is about to leave Europe for an installation in the fall of 2018. Meanwhile, the interferometer infrastructure has continuously improved in performance, in term of transmission and vibrations, when used with both the Unit Telescopes and Auxiliary Telescopes. These are the highlights of the last two years of the VLTI 2nd generation upgrade started in 2015.
The New Adaptive Optics Module for Interferometry (NAOMI) is ready to be installed at the 1.8-metre Auxiliary Telescopes (ATs) at ESO Paranal. NAOMI will make the existing interferometer performance less dependent on the seeing conditions. Fed with higher and more stable Strehl, the fringe tracker will achieve the fringe stability necessary to reach the full performance of the second-generation instruments GRAVITY and MATISSE. All four ATs will be equipped between September and November 2018 with a Deformable mirror (ALPAO DM-241), a 4*4 Shack– Hartmann adaptive optics system operating in the visible and an RTC based on SPARTA Light. During the last 6 months thorough system test has been made in laboratory to demonstrate the Adaptive Optics and chopping capability of NAOMI.
In this paper we will report on the status of the instrumentation project for the European Southern Observatory's Extremely Large Telescope (ELT). Three instruments are in the construction phase: HARMONI, MICADO and METIS. The multi-conjugate adaptive optics system for MICADO, MAORY, is also under development. Preliminary Design Reviews of all of these systems are planned to be completed by mid-2019. The construction of a laser tomographic module for HARMONI is part of "Phase 2" of the ELT: the design has been advanced to Preliminary Design level in order to define the interface to the HARMONI spectrograph. Preparations for the next instruments have also been proceeding in parallel with the development of these instruments. Conceptual design studies for the multi-object spectrograph MOSAIC, and for the high resolution spectrograph HIRES have been completed and reviewed. We present the current design of each of these instruments and will summarise the work ongoing at ESO related to their development.
The Meteosat Third Generation (MTG) Programme will ensure the future continuity and enhancement of meteorological data from geostationary orbit as currently provided by the Meteosat Second Generation (MSG) system. The industrial prime contractor for the space segment is Thales Alenia Space (France), with a core team consortium including OHB System AG (Germany).
ERIS will be the next-generation AO facility on the VLT, combining the heritage of NACO imaging, with the spectroscopic capabilities of an upgraded SINFONI. Here we report on the all-new NIX imager that will deliver diffraction-limited imaging from the J to M band. The instrument will be equipped with both Apodizing Phase Plates and Sparse Aperture Masks to provide high-angular resolution imagery, especially suited for exoplanet imaging and characterization. This paper provides detail on the instrument’s design and how it is suited to address a broad range of science cases, from detailed studies of the galactic centre at the highest resolutions, to studying detailed resolved stellar populations.
A suite of seven instruments and associated AO systems have been planned as the "E-ELT Instrumentation Roadmap". Following the E-ELT project approval in December 2014, rapid progress has been made in organising and signing the agreements for construction with European universities and institutes. Three instruments (HARMONI, MICADO and METIS) and one MCAO module (MAORY) have now been approved for construction. In addition, Phase-A studies have begun for the next two instruments - a multi-object spectrograph and high-resolution spectrograph. Technology development is also ongoing in preparation for the final instrument in the roadmap, the planetary camera and spectrograph. We present a summary of the status and capabilities of this first set of instruments for the E-ELT.
The upgrade of the VLTI infrastructure for the 2nd generation instruments is now complete with the transformation of the laboratory, and installation of star separators on both the 1.8-m Auxiliary Telescopes (ATs) and the 8-m Unit Telescopes (UTs). The Gravity fringe tracker has had a full semester of commissioning on the ATs, and a first look at the UTs. The CIAO infrared wavefront sensor is about to demonstrate its performance relative to the visible wavefront sensor MACAO. First astrometric measurements on the ATs and astrometric qualification of the UTs are on-going. Now is a good time to revisit the performance roadmap for VLTI that was initiated in 2014, which aimed at coherently driving the developments of the interferometer, and especially its performance, in support to the new generation of instruments: Gravity and MATISSE.
The New Adaptive Optics Module for Interferometry (NAOMI) will be developed for and installed at the 1.8-metre Auxiliary Telescopes (ATs) at ESO Paranal. The goal of the project is to equip all four ATs with a low-order Shack– Hartmann adaptive optics system operating in the visible. By improving the wavefront quality delivered by the ATs for guide stars brighter than R = 13 mag, NAOMI will make the existing interferometer performance less dependent on the seeing conditions. Fed with higher and more stable Strehl, the fringe tracker(s) will achieve the fringe stability necessary to reach the full performance of the second-generation instruments GRAVITY and MATISSE.
ESO is undertaking a large upgrade of the infrastructure on Cerro Paranal in order to integrate the 2nd generation of interferometric instruments Gravity and MATISSE, and increase its performance. This upgrade started mid 2014 with the construction of a service station for the Auxiliary Telescopes and will end with the implementation of the adaptive optics system for the Auxiliary telescope (NAOMI) in 2018. This upgrade has an impact on the infrastructure of the VLTI, as well as its sub-systems and scientific instruments.
ERIS is the new AO instrument for VLT-UT4 led by a Consortium of Max-Planck Institut fuer Extraterrestrische Physik, UK-ATC, ETH-Zurich, ESO and INAF. The ERIS AO system provides NGS mode to deliver high contrast correction and LGS mode to extend high Strehl performance to large sky coverage. The AO module includes NGS and LGS wavefront sensors and, with VLT-AOF Deformable Secondary Mirror and Laser Facility, will provide AO correction to the high resolution imager NIX (1–5um) and the IFU spectrograph SPIFFIER (1–2.5um). In this paper we present the preliminary design of the ERIS AO system and the estimated correction performance.
Due to the exposed location of the Wendelstein observatory on the steep summit of mount Wendelstein no road exists to
transport telescope components and heavy equipment to the observatory in order to install the new 2m Fraunhofer
Telescope Wendelstein (FTW) in its new dome. A two step installation concept was therefore followed to mitigate any
risks that essential hardware would not work once installed on the mountain.
This paper reports on the telescope factory assembly and tests, including on-sky tests, which were performed in early
summer 2011 at the factory site to make sure, that the telescope and all essential subsystems are working properly before
the telescope would be installed on the mountain. The telescope was disassembled again to be transported to the
mountain in summer. Lifting of all structural subsystems and the optics up to the mountain observatory with the help of a
heavy lift helicopter will be presented in detail, also looking at specific design drivers, logistic aspects and special tools
for installation of the telescope and its mirrors in its new dome. Handling and transport concept for the M1 mirror
installation, which also will have to be used when the mirror is disassembled for recoating, are presented. Up to end of
2011 the telescope installation and pre-alignment could be completed including first on-sky tests. The system will
undergo a detailed performance test campaign in the first halve of 2012. Current performance results of these
commissioning activities will be reported.
Subaru adaptive optics system (AO188) is an 188-elements curvature sensor adaptive optics system that is operated
in both natural and laser guide star modes. AO188 was installed at Nasmyth platform of the Subaru
telescope and it has been successfully operating in the natural guide star mode since October 2008. The performance
of AO188 in the natural guide star mode has been well verified from on-sky data obtained with the infrared
camera and spectrograph (IRCS). Under normal seeing condition, AO188 achieves K-band Strehl ratio between
60% and 70% using R = 9.0 magnitude natural guide stars and it works well with faint guide stars down to
R = 16.5 magnitude. We measured the FWHM and Strehl ratio of stellar images in globular clusters and found
that the isoplanatic angle is approximately 30 arcsec. In this paper, we describe an overview of the operation
procedure for AO188, as well as its performance such as angular resolution, Strehl ration, and sensitivity gain
for detecting faint objects.
We are developing a laser guide star (LGS) system for the
188-elements Adaptive Optics system (AO188) of the
Subaru telescope. In this paper we describe the results of the performance tests of the LGS system. The beam
that excites sodium atoms at 90 km altitude of the LGS is generated by the following sequence. The source
of the beam is a quasi-CW mode locked sum-frequency generating 589 nm laser. This laser beam propagates
through a diagnostics system for measuring the wavelength and the beam quality. Then it couples into a solidcore
photonic crystal fiber cable for transmitting the beam to a telescope for launching the beam (LLT: Laser
Launching Telescope). The output beam from this fiber cable is collimated by the optics mounted on the
LLT. This collimated beam is expanded by the LLT and launched into the sky. We executed several engineering
observations of the LGS system from 2009 for confirming the performance of all the components in this sequence.
We also report the quality of the LGS.
The Subaru laser guide star adaptive optics system (AO188) was installed at the Nasmyth focus of the Subaru
Telescope on October 2006 and it is in operation with the natural guide star (NGS) mode. The operation of
the laser guide star (LGS) mode started on January 2010. A visible low-order wavefront sensor (LOWFS) was
built to measure tip-tilt and defocus terms of wavefront by using a single NGS within a 2.7 arcmin diameter field
when an LGS is used for high-order wavefront sensing with the 188-element curvature based wavefront sensor.
This LOWFS is a 2 × 2 sub-aperture Shack-Hartmann sensor with 16 photon-counting avalanche photodiode
(APD) modules. A 4×4-element lenslet array is located after the 2 × 2 sub-aperture Shack-Hartmann lenslet
array and it is coupled with the APD modules through optical fibers. The field of view of the LOWFS is 4 arcsec
in diameter. It has own guide star acquisition unit, acquisition and pupil cameras, and atmospheric dispersion
corrector. We describe the design, construction, and integration of this low-order wavefront sensor.
We report recent development in real time control system of Subaru adaptive optics system. The main topic is
modification of the real time control system for laser guide star operation. The primary change is appending lower order
wave-front sensor. And also, an auxiliary tip-tilt and focus control are appended before higher order waver-front sensor
to absorb the perturbation of the laser beam and height of sodium layer. Our implementations using the control gain
matrix are introduced thoroughly from the basis of the system design and down to the details. Also, other new function
and prospects in the near future will be presented for the cascaded average monitor and the time domain over sampling.
KEYWORDS: Telescopes, Mirrors, Adaptive optics, Telecommunications, Secondary tip-tilt mirrors, Infrared telescopes, Digital signal processing, Control systems, Infrared radiation, Data conversion
A tip/tilt off-load function from AO188 deformable mirror mount to Subaru telescope infrared secondary mirror
has been implemented and tested. The function is effective to reduce the influence of strong background pattern
at thermal infrared wavelengths. We describe the function and report the test results in this paper.
In this paper, we present the science path ADC unit (atmospheric dispersion corrector) for the AO188 Adaptive
Optics System of the Subaru Telescope. The AO188 instrument is a curvature-based Adaptive Optics system with
188 subapertures and achieves good correction down to shorter wavelengths like J-band. At these wavelengths, the
atmospheric dispersion within the band becomes significant and thus a correction of the atmospheric dispersion
is essential to reach diffraction-limited image quality. We give an overview of the requirements, the final optical
and mechanical design of the ADC unit, as well as the structure of its control software.
The current status of commissioning and recent results in performance of Subaru laser guide star adaptive optics
system is presented. After the first light using natural guide stars with limited configuration of the system in
October 2006, we concentrated to complete a final configuration for a natural guide star to serve AO188 to an
open use observation. On sky test with full configurations using natural guide star started in August 2008, and
opened to a public one month later. We continuously achieved around 0.6 to 0.7 of Strehl ratio at K band using
a bright guide star around 9th to 10th magnitude in R band. We found an unexpectedly large wavefront error
in our laser launching telescope. The modification to fix this large wavefront error was made and we resumed
the characterization of a laser guide star in February 2009. Finally we obtained a round-shaped laser guide star,
whose image size is about 1.2 to 1.6 arcsec under the typical seeing condition. We are in the final phase of
commissioning. A diffraction limited image by our AO system using a laser guide star will be obtained in the
end of 2010. An open use observation with laser guide star system will start in the middle of 2011.
The image derotator is an integral part of the AO188 System at Subaru Telescope. In this article software control,
characterization and integration issues of the image derotator for AO188 System presented. Physical limitations of the
current hardware reviewed. Image derotator synchronization, tracking accuracy, and problem solving strategies to
achieve requirements presented. It's use in different observation modes for various instruments and interaction with the
telescope control system provides status and control functionality. We describe available observation modes along with
integration issues. Technical solutions with results of the image derotator performance presented. Further improvements
and control software for on-sky observations discussed based on the results obtained during engineering observations.
An overview of the requirements, the final control method, and the structure of its control software is shown. Control
limitations and accepted solutions that might be useful for development of other instrument's image derotators presented.
Laboratory and on-sky experience suggests that the integration of big astronomical instruments, specially of a
complex interferometric system, is a challenging process. LINC-NIRVANA is the Fizeau interferometric imager
for the Large Binocular Telescope (LBT). Simulating the final operating environment of every system component
has shown how critical is the presence of flexures, vibrations and thermal expansion. Assembling and aligning
the opto-mechanical sub-systems will require an absolute reference which is not affected by static displacements
or positioning errors.
A multi-purpose calibration unit has been designed to ensure the quality of the alignment of optics and
detectors and the reliability of the mechanical setup. This new compact and light-weighted unit is characterized
by sophisticated kinematics, simple mechanical design and composite materials. In addition, the reduced number
of motorized axis improves the stiffness and lowers the angular displacements due to moving parts. The modular
concept integrates several light sources to provide the proper calibration reference for the different sub-systems
of LINC-NIRVANA. For the standard alignment of the optics an absolute reference fiber will be used. For flatfielding
of the detectors the unit provides an integrating sphere, and a special rotating multi-fiber plate (infrared
and visible) is used to calibrate the advanced adaptive optics and the fringe-tracking systems. A module to
control non-common path aberrations (Flattening of Deformable Mirrors) is also provided.
HiCIAO is a near-infrared, high contrast instrument which is specifically designed for searches and studies for
extrasolar planets and proto-planetary/debris disks on the Subaru 8.2 m telescope. A coronagraph technique
and three differential observing modes, i.e., a dual-beam simultaneous polarimetric differential imaging mode,
quad-beam simultaneous spectral differential imaging mode, and angular differential imaging mode, are used
to extract faint objects from the sea of speckle around bright stars. We describe the instrument performances
verified in the laboratory and during the commissioning period. Readout noise with a correlated double sampling
method is 15 e- using the Sidecar ASIC controller with the HAWAII-2RG detector array, and it is as low as 5 e-
with a multiple sampling method. Strehl ratio obtained by HiCIAO on the sky combined with the 188-actuator
adaptive optics system (AO188) is 0.4 and 0.7 in the H and K-band, respectively, with natural guide stars that
have R ~ 5 and under median seeing conditions. Image distortion is correctable to 7 milli-arcsec level using
the ACS data as a reference image. Examples of contrast performances in the observing modes are presented
from data obtained during the commissioning period. An observation for HR 8799 in the angular differential
imaging mode shows a clear detection of three known planets, demonstrating the high contrast capability of
AO188+HiCIAO.
We present in this paper the status of the calibration unit for the interferometric infrared imager LINC-NIRVANA
that will be installed on the Large Binocular Telescope, Arizona. LINC-NIRVANA will combine high angular
resolution (~10 mas in J), and wide field-of-view (up to 2'×2') thanks to the conjunct use of interferometry
and MCAO. The goal of the calibration unit is to provide calibration tools for the different sub-systems of the
instrument. We give an overview of the different tasks that are foreseen as well as of the preliminary detailed
design. We show some interferometric results obtained with specific fiber splitters optimized for LINC-NIRVANA.
The different components of the calibration unit will be used either during the integration phase on site, or during
the science exploitation phase of the instrument.
KEYWORDS: Point spread functions, Modulation transfer functions, Telescopes, Wavefront aberrations, Fizeau interferometers, Sensors, Atmospheric optics, Spatial resolution, Mirrors, K band
A Fizeau interferometer combines the light of several telescopes to obtain panoramic images with an angular
resolution equivalent to the longest edge-to-edge separation in the system. The overall performance of a Fizeau
interferometer depends critically on the performance of the (MC)AO system and the efficiency of atmospheric
piston correction, but also on other effects like alignment accuracies, filter bandwidths, tracking errors, atmospheric
dispersion and field rotation. Due to the mutual dependence, Strehl ratio or fringe contrast like in
conventional Adaptive Optics systems or pupil plane interferometers are not sufficient for a consice assessment
of the performance of such an instrument. As a measure for the actual performance, we propose to use the ratio
R23, which is the actual high-spatial frequency information in the images, divided by what could be measured
in principal with a 23m telescope (as the LBT). We present the theoretical concept of this method and show
the results of various simulations of the abovementioned effects as an application to LINC-NIRVANA, a Fizeau
interferometer currently being built for the LBT.
LINC-NIRVANA is the near-infrared homothetic imaging camera for the Large Binocular Telescope. Once
operational, it will provide an unprecedented combination of angular resolution, sensitivity and field of view. Its
Fringe and Flexure Tracking System (FFTS) is mandatory for an efficient interferometric operation of LINC-NIRVANA.
It is tailored to compensate low-order phase perturbations in real-time to allow for a time-stable
interference pattern in the focal plane of the science camera during the integration. Two independent control
loops are realized within FFTS: A cophasing loop continuously monitors and corrects for atmospheric and
instrumental differential piston between the two arms of the interferometer. A second loop controls common
and differential image motion resulting from changing orientations of the two optical axes of the interferometer.
Such changes are caused by flexure but also by atmospheric dispersion.
Both loops obtain their input signals from different quadrants of a NIR focal plane array. A piezo-driven
piston mirror in front of the beam combining optics serves as actuator in the cophasing loop. Differential piston
is determined by fitting a parameterized analytical model to the observed point spread function of a reference
target. Tip-tilt corrections in the flexure loop are applied via the secondary mirrors. Image motion is sensed for
each optical axis individually in out-of-focus images of the same reference target.
In this contribution we present the principles of operation, the latest changes in the opto-mechanical design,
the current status of the hardware development.
Since November 2004 we measured the optical turbulence (C2N
profiles) with a Generalized Scidar (GS) placed at
the focus of the Vatican Advanced Technology Telescope at Mt.Graham, Arizona. The present statistic consists
in measurements related to 43 nights covering different periods of the solar year. In this paper we calculate the
statistics of the astroclimatic parameters
(C2N, seeing ε , isoplanatic angle θ0, wavefront coherence time τ0) and
we compare these values with those measured above other top level astronomic sites. All profiles are reduced
into a form suitable to be used as inputs for adaptive optics point spread function simulations for the conceptual
design of the Laser Guide Star Facility supported by a GLAO system of the Large Binocular Telescope. With
GS measurements done observing wide binaries (30-35 arcsec), the turbulence in the first kilometer above the
ground is characterized with the vertical resolution (200-250 m) required for the optimization of a 4 arcmin
field of view AO system. It is the first time that are published measurements of the optical turbulence vertical
distribution above a mid-latitude site with such a high vertical resolution and such a high statistical reliability.
On 8 of those nights, employing cross-correlation scintillation maps of wide binaries and the method described
in Ref.[1] we characterize the distribution of the optical turbulence in the first kilometer at the extremely high
vertical resolution of 20-30 meters.
LINC-NIRVANA is an infrared camera that will work in Fizeau interferometric way at the Large Binocular Telescope
(LBT). It will take advantage of a field corrected from two MCAO systems, one for each arm, based on the Layer
Oriented Technique and using solely Natural Guide Stars. For each arm, there will be two wavefront sensors, one
conjugated to the Ground and one conjugated to a selectable altitude, ranging from 4 to 15 Km. They will explore
different fields of view for the wavefront sensing operations, accordingly to the Multiple Field of View concept, and
particularly the inner 2 arcminutes FoV will be used to select the references for the high layer wavefront sensor while the
ground one will explore a wider anular field, going from 2 to 6 arcminutes in diameter. The wavefront sensors are under
INAF responsibility, and their construction is ongoing in different italian observatories. Here we report on progress, and
particularly on the test ongoing in Padova observatory on the Ground Layer Wavefront Sensor.
LINC-NIRVANA (LN) is a German-Italian Fizeau (imaging) interferometer for the Large Binocular Telescope
(LBT). The Instrument Control Software (ICS) of this instrument is a hierarchical, distributed software package,
which runs on several computers. In this paper we present the bottom layer of the hierarchy - the Basic
Device Application (BASDA) layer. This layer simplifies the development of the ICS through a general driver
architecture, which supports different types of hardware. This generic device architecture provides a high level
interface to encapsulate the hardware dependent driver. The benefit of such a device architecture is to keep the
basic device-driver layer flexible and independent from the hardware, and to keep the hardware transparent to
the ICS. Additionally, the basic device-driver layer supports interfaces to IDL based applications for calibration
and laboratory testing of astronomical instruments, and interfaces to engineering GUIs that allow to maintain
the software components easily.
LINC-NIRVANA is an infrared camera working in Fizeau interferometric mode. The beams coming from the two
primary mirrors of the LBT are corrected for the effects of the atmospheric turbulence by two Multi-Conjugate Adaptive
Optics (MCAO) systems, working in a scientific field of view of 2 arcminutes. One single arm MCAO system includes
two wave-front sensors, driving two deformable mirrors, one for the ground layer correction (LBT secondary mirror)
and one for the correction of a mid-high layer (up to a maximum distance of 15 km). The first of the two Mid-High
Wavefront Sensors (MHWS) was integrated and tested as a stand-alone unit in the laboratory at INAF-Osservatorio
Astronomico di Bologna, where the telescope was simulated by means of a simple afocal system illuminated by a set of
optical fibers. Then the module was delivered to the MPIA laboratories in Heidelberg, where is going to be integrated
and aligned to the post-focal optical relay of one LINC-NIRVANA arm, including the deformable mirror. A number of
tests are in progress at the moment of this writing, in order to characterize and optimize the system functionalities and
performance. A report is presented about the status of this work.
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.).
Adaptive optics (AO) allows one to derive the point spread function (PSF) simultaneously to the science image,
which is a major advantage in post-processing tasks such as astrometry/photometry or deconvolution. Based on
the algorithm of Veran et al. (1997), PSF reconstruction has been developed for four different AO systems so far:
PUEO, ALFA, Lick-AO and Altair. A similar effort is undertaken for NAOS/VLT in a collaboration between
the group PHASE (Onera and Observatoire de Paris/LESIA) and ESO. In this paper, we first introduce two
new algorithms that prevent the use of the so-called "Uij functions" to: (1) avoid the storage of a large amount
of data (for both new algorithms), (2) shorten the PSF reconstruction computation time (for one of the two)
and (3) provide an estimation of the PSF variability (for the other one). We then identify and explain issues in
the exploitation of real-time Shack-Hartmann (SH) data for PSF reconstruction, emphasising the large impact
of thresholding in the accuracy of the phase residual estimation. Finally, we present the data provided by the
NAOS real-time computer (RTC) to reconstruct PSF ((1) the data presently available, (2) two NAOS software
modifications that would provide new data to increase the accuracy of the PSF reconstruction and (3) the tests
of these modifications) and the PSF reconstruction algorithms we are developing for NAOS on that basis.
The Mid-High Wavefront Sensors (MHWS) are components of the adaptive optics system of LINC-NIRVANA, the Fizeau interferometer that will be mounted at the LBT. These sensors, one for each telescope arm, will measure the atmospheric turbulence in the high altitude layers, using up to 8 reference stars in a 2 arcmin Field of View, and they will be coupled with two Ground Layer WFSs that will measure the lower part of the atmospheric turbulence using up to 12 stars over an annular Field of View from 2 to 6 arcmin in diameter. We will describe the opto-mechanical layout of the MHWS and the Assembly, Integration and Test (AIT) phase of the first sensor in the laboratory of the Bologna Observatory.
ELTs depend on Adaptive Optics (AO) to reach the diffraction limit. To achieve sufficient sky coverage with AO, several Laser Guide Stars (LGS) will be needed, but the finite distance of the LGSs introduces optical problems which can not be solved easily, especially at telescopes with a diameter larger than 30m. PIGS (Pseudo Infinite Guide Star) is a novel sensing technique proposed to overcome some of these problems by using a slit mask and a reflective rod measuring in radial and azimuthal direction the wavefront abberations. The sensor was already demonstrated with a single LGS in laboratory and on sky. Currently we investigate the PIGS concept in a MCAO (Multi Conjugated Adaptive Optics) fashion by building a test setup in the laboratory. MCAO will solve the cone effect, one of the remaining problems with PIGS. The PIGS MCAO experiment goals on engineering problems and demonstration of the layer orientated concept with the PIGS technique. The PIGS concept and its extension to MCAO will be described and preliminary results presented.
We present a laboratory setup of a Ground-Layer Adaptive Optics system. This system is a scaled-down version of the MCAO system of MAD (a MCAO system for the VLT) / LINC-NIRVANA (a Fizeau Imager for the LBT) and measures the wavefront aberrations with 4 pyramids in a layer-oriented fashion with optical co-addition. The laboratory setup contains besides the wavefront-sensing unit a telescope-simulator, a dynamic turbulence generator and a Deformable Mirror for the wavefront correction. We describe the overall system and its single components, open- and closed-loop measurements of the characteristics of a system working in GLAO mode and first results when using a Kalman filter for the control of the wavefront reconstruction process.
LINC-NIRVANA is an infrared camera that will work in Fizeau interferometric way at the Large Binocular Telescope (LBT). The two beams that will be combined in the camera are corrected by an MCAO system, aiming to cancel the turbulence in a scientific field of view of 2 arcminutes. The MCAO wavefront sensors will be two for each arm, with the task to sense the atmosphere at two different altitudes (the ground one and a second height variable between a few kilometers and a maximum of 15 kilometers). The first wavefront sensor, namely the Ground layer Wavefront sensor (GWS), will drive the secondary adaptive mirror of LBT, while the second wavefront sensor, namely the Mid High layer Wavefront Sensor (MHWS) will drive a commercial deformable mirror which will also have the possibility to be conjugated to the same altitude of the correspondent wavefront sensor. The entire system is of course duplicated for the two telescopes, and is based on the Multiple Field of View (MFoV) Layer Oriented (LO) technique, having thus different FoV to select the suitable references for the two wavefront sensor: the GWS will use the light of an annular field of view from 2 to 6 arcminutes, while the MHWS will use the central 2 arcminutes part of the FoV. After LINC-NIRVANA has accomplished the final design review, we describe the MFoV wavefront sensing system together with its current status.
The 8 m SUBARU telescope atop Mauna Kea on Hawaii will shortly be equipped with a 188 actuator adaptive optics system (AO 188). Additionally it will be equipped with a Laser guide star (LGS) system to increase the sky coverage of that system. One of the additional tip-tilt sensor which is required to operate AO 188 in LGS mode will be working in the infrared to further enhance the coverage in highly obscured regions of the sky. Currently, various options for this sensor are under study, however the baseline design is a pyramid wavefront sensor. It is currently planned to have this sensor be able to provide also information on higher modes in order to feed AO 188 alone, i.e. without the LGS when NIR-bright guide stars are available. In this paper, we will present the results of the basic design tradeoffs, the performance analysis, and the project plan. Choices to be made concern the number of subapertures available across the primary mirror, the number of corrected modes, control of the AO system in combination with and without LGS, the detector of the wavefront sensor, the operation wavelength range and so forth. We will also present initial simulation results on the expected performance of the device, and the overall timeline and project structure.
By using the SCIDAR instrument at the VATT on the top of Mt. Graham and a very wide binary star with a separtion of 35", the vertical structure of the turbulence in the first few hundred meters above the telescope was measured. When using such a binary and analysing the cross-correlation images, a vertical resolution for the turbulence profile of a few tens of meters can be achieved near the ground. This permits to determine the inner structure and the wind sheer of the single turbulent layers inside the ground-layer. We present the principles and the data-reduction process of this method and show first results obtained with this method at Mt. Graham. As an application, we estimate the fraction of the turbulence between the dome of the VATT and the primary mirror of the LBT.
Combining the two 8.4 m telescopes of the Large Binocular Telescope 1(LBT) offers the unique possibility to achieve diffraction limited images with 23 m spatial resolution. This requires an interferometric superposition of the two telescope beams in a Fizeau-type interferometer. LINC-NIRVANA delivers a 10 arcsec x 10 arcsec panoramic field of view with 5 mas pixel size. In addition to delivering diffraction limited, single-telescope images, the optics have several additional constraints imposed by interferometric operation. In this paper, we describe the evolution of the optical design and how the individual optical subsystems were developed in parallel to provide optimal combined performance. We also present an alignment strategy to setup the optics and to achieve zero optical path difference.
We present recent results of the atmospheric turbulence measured with a Generalized SCIDAR at Mt. Graham, running for 16 nights in 2004 and 2005 at the focus of the VATT Telescope. The principle of the data reduction process is shown, as well as the validation of the obtained results. From the reduced C2N and wind-speed profiles, together with an estimate for the dome-seeing, the astroclimatic parameters such as seeing ε, isoplanatic angle υ0 and wavefront coherence time τ0 are calculated. We obtained median values for ε (0.67"±0.17"), υ0 (2.71"±1.11") and τ0 (3.63msec ± 1.66msec), which indicate that Mt. Graham is as an astronomical site comparable to the best ones in the world. As an application, the calculated C2N profiles were used together with layer-transfer functions for a MCAO system to estimate the optimal conjugated heights of the DMs for the MCAO system of LINC-NIRVANA.
We built an optical system that emulates the optical characteristics of an 8m-class telescope like the VLT and that
contains rotating glass plates phase screens to generate realistic atmosphere-like optical turbulence. Together
with an array of single mode fibers fed from white light sources to simulate various stellar configurations, we can
investigate the behavior of different single or multi-conjugate adaptive optics setups. In this paper we present
the characteristics of phase screens etched on glass plates surfaces obtained from Silios Technologies.
Deformable mirrors with more than 1000 actuators are currently being
developed for eXtreme AO applications, either for ELTs, high order
Adaptive Optics correction in the visible light, or combination of
both. The large number of actuators, the high frequency at which
these DMs are to be used and further advancement in schemes for AO
control, requiring a growing degree of knowledge of the AO system
for efficient correction, sets special requirements on the
characterization of the static and dynamic behavior of the DM. In
the light of CHEOPS, an extreme-AO Planet Finder project, we have
characterized a Xinetics deformable mirrors with 349 actuators.
This mirror serves as a proxy for the characterization of a >1200
actuator DM of a similar type, which will be implemented in CHEOPS.
In this paper we present the results of this characterization.
Special attention was paid to mirror properties like hysteresis,
non-linearity, temperature dependence and influence function.
LINC-NIRVANA is an imaging interferometer for the Large Binocular Telescope (LBT) and will make use of multi-conjugated adaptive optics (MCAO) with two 349 actuators deformable mirrors (DM), two 672 actuator deformable secondary mirrors and a total of 4 wavefront sensors (WFS) by using 8 or 12 natural guide stars each. The goal of the MCAO is to increase sky coverage and achieve a medium Strehl-ratio over the 2 arcmin field of view. To test the concepts and prototypes, a laboratory setup of one MCAO arm is being built. We present the layout of the MCAO prototype, planned and accomplished tests, especially for the used Xinetics DMs, and a possible setup for a test on sky with an existing 8m class telescope.
On the way to the Extremely Large Telescopes (ELT) the Large Binocular
Telescope (LBT) is an intermediate step. The two 8.4m mirrors create a masked aperture of 23m. LINC-NIRVANA is an instrument taking advantage of this opportunity. It will get, by means of Multi-Conjugated Adaptive Optics (MCAO), a moderate Strehl Ratio over a 2 arcmin field of view, which is used for Fizeau (imaging) interferometry in J,H and K. Several MCAO concepts, which are
proposed for ELTs, will be proven with this instrument. Studies of sub-systems are done in the laboratory and the option to test them on sky are kept open. We will show the implementation of the MCAO concepts and control aspects of the instrument and present the road map to the final installation at LBT. Major milestones of LINC-NIRVANA, like preliminary design review or final design review are already done or in preparation. LINC-NIRVANA is one of the
few MCAO instruments in the world which will see first light and go into operation within the next years.
The first complete seasonal variation study extended over 1 year
(~80 nights uniformly distributed along twelve months) of all
the principal astroclimatic parameters (CN2, seeing ε, wavefront coherence time τO, isoplanatic angle θ0, scintillation rate σI2, isoplanatic angle for the MCAO θM - where M is the number of the deformable mirrors DMs - M=1,2,3,...) simulated with an atmospherical model (Meso-Nh) above the San Pedro Martir Observatory is presented. The atmospherical model run in an autonomous way to simulate CN2 and wind speed vertical profiles (over ~20 km) related to the 80 nights after it has been calibrated with the support of a few CN2 measurements. All the integrated parameters are calculated using these two basic
elements and general seasonal trends are put in evidence.
The impact of our results on the adaptive optics techniques (AO)
is discussed as well as the potentialities of the numerical simulations as a new tool for the climatologic analysis of the optical turbulence above astronomical sites.
Several multi-conjugate adaptive optics (MCAO) systems using the layer-oriented approach are under construction and will soon be tested at different facilities in several instruments. One of these instruments is LINC-NIRVANA, a Fizeau interferometer for the Large Binocular Telescope (LBT). This instrument uses a ground layer wavefront sensor (GWS) and a combined mid-high layer wavefront sensor (MHWS) with different fields of view (concept of multiple field of view), a 2-6 arcmin annular ring for the GWS and a 2 arcmin diameter central field of view for the MHWS. Both sensors are Pyramid wavefront sensors which optically co-add light from multiple natural guide stars.
The opto-mechanical problems concerning these sensors are related to the fast focal ratio of the beam on the pyramids coupled with the available pixelscale of detectors. This leads to very tight requirements on the moving systems (linear stages) for the star enlargers (SE) used to pick off the light of individual stars.
As there are 40 star enlargers in the overall system, additional efforts were put into the alignment system of the optics of the star enlargers and the reduction in size of the star enlargers to minimize the distance between available guide stars.
We present a 1:3 scale model of the LINC-NIRVANA interferometer. This
laboratory Fizeau, or image plane, interferometer allows us to test many aspects of LINC-NIRVANA before the final instrument is integrated. We have used this testbed interferometer to practice alignment procedures, verify the optical design, show that point spread functions with low (10\%) Strehl ratio can maintain high fringe contrast, and test the fringe tracking algorithm by running the interferometer in a closed piston loop.
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