This paper presents an update on the construction, testing, and commissioning of the SDSS-V Local Volume Mapper (LVM) telescope system. LVM is one of three surveys that form the fifth generation of the Sloan Digital Sky Survey, and it will employ a coordinated network of four, 16-cm telescopes feeding three fiber spectrographs at the Las Campanas Observatory. The goal is to spectrally map approximately 2500 square degrees of the Galactic plane with 37” spatial resolution and R~4000 spectral resolution over the wavelength range 360-980 nm. LVM will also target the Magellanic Clouds and other Local Group galaxies. Each of the four LVM telescopes consists of a two-mirror siderostat in alt-alt configuration feeding an optical breadboard. This produces a fixed, stable focal plane for the fiber-based Integral Field Unit (IFU). One telescope hosts the science IFU, while two others observe adjacent fields to calibrate geocoronal emission. The fourth telescope makes rapid observations of bright stars to compensate telluric absorption. The entrance slits of the spectrographs intersperse the fibers from all three types of telescope, producing truly simultaneous science and calibration exposures. We summarize the final design of the telescope system and report on its construction, alignment and testing in the laboratory. We also describe our deployment plan for commissioning at LCO, anticipated for late 2022.
The Local Volume Mapper (LVM) project is one of three surveys that form the Sloan Digital Sky Survey V. It will map the interstellar gas emission in a large fraction of the southern sky using wide-field integral field spectroscopy. Four 16-cm telescopes in siderostat configuration feed the integral field units (IFUs). A reliable acquisition and guiding (A&G) strategy will help ensure that we meet our science goals. Each of the telescopes hosts commercial CMOS cameras used for A&G. In this work, we present our validation of the camera performance. Our tests show that the cameras have a readout noise of around 5.6 e- and a dark current of 21 e-/s, when operated at the ideal gain setting and at an ambient temperature of 20 °C. To ensure their performance at a high-altitude observing site, such as the Las Campanas Observatory, we studied the thermal behaviour of the cameras at different ambient pressures and with different passive cooling solutions. Using the measured properties, we calculated the brightness limit for guiding exposures. With a 5 s exposure time, we reach a depth of ∼16.5 Gaia gmag with a signal-to-noise ratio (SNR) < 5. Using Gaia Early Data Release 3, we verified that there are sufficient guide stars for each of the ∼25 000 survey pointings. For accurate acquisition, we also need to know the focal plane geometry. We present an approach that combines on-chip astrometry and using a point source microscope to measure the relative positions of the IFU lenslets and the individual CMOS pixels to around 2 µm accuracy.
MICADO is the Multi-AO Imaging Camera for Deep Observations, a first light instrument for the Extremely Large Telescope (ELT). The instrument will be assisted by a Single-Conjugate Adaptive Optics (SCAO) system and the Multi conjugate Adaptive Optics RelaY (MAORY). MICADO can operate in the so-called stand-alone mode in the absence of MAORY with the SCAO correction alone. Here, we present the opto-mechanical final design of the Relay Optics (RO), the optical system relaying the ELT focal plane to an accessible position of MICADO for that SCAO-only stand-alone observing mode. The RO consists of an optical bench made of carbon fiber reinforced plastic (CFRP), an optical assembly made of three flat, motorized tip-tilt-piston mirrors and three powered mirrors of up to ~500 mm in diameter, the MICADO calibration assembly and a cover to protect all opto-mechanical components on top of the bench. A 9-point whiffletree support, combined with a thermal compensation system is implemented for the critical flat mirror (M6), while a more simple 3- point support is employed for the other two flat mirror M1 and M5. The powered mirrors (M2, M3, M4) comprising the relay's three mirror anastigmat (TMA) are supported by V-shape mounts. The static and the dynamic performance of the MICADO RO are investigated through a detailed Finite Element Analysis (FEA), whose results are combined with a Zernike basis representation of the surface deformations performed in Zemax for assessing the optical performance. The variation of the mirror position due to the operational temperature drift Delta T and other disturbances, is also considered in an end-to-end simulation. The required overall wavefront error of 100 nm rms is fulfilled with the current design proposal. Additionally, the results of a motorized tip-tilt-piston mirror mount prototype are presented as well..
METIS, the Mid-infrared Imager and Spectrograph for the Extremely Large Telescope (ELT), is one of the three first generation science instruments and about to complete its final design phase [1]. The Imager sub-system provides diffraction-limited imaging capabilities and low-resolution grism-spectroscopy in two channels: one covers the atmospheric LM bands with a field of view of 11x11 arcsec, and the second covers the N band, with a field of view of 14x14 arcsec. Both channels have a common collimator and a dichroic beam splitter dividing the light into two dedicated cameras and the corresponding detectors. In addition, the Imager provides a precise pupil re-imaging implementation allowing the positioning of high-contrast imaging masks for coronagraphic applications. The two channels are equipped with a HAWAII-2RG detector for LM-band and a GeoSnap detector for the N-band. We present the final optical design of the Imager in a summary, as well as the cryo-mechanical concept. The mechanical design gives an overview of the general design aspects and the analyses that demonstrate the approach how to deal with demanding stability and alignment requirements for high-contrast imaging. It further focuses on the design of individual units as e.g., on the GeoSnap detector mount and on the pupil re-imager. In addition, we exemplarily outline some of the key alignment and verification tasks, essential to guarantee the performance of the Imager.
The Sloan Digital Sky Survey V (SDSS-V) is an all-sky spectroscopic survey of <6 million objects, designed to decode the history of the Milky Way, reveal the inner working of the stars, investigate the origin of solar systems, and track the growth of supermassive black holes across the Universe. The Local Volume Mapper (LVM) is one of three surveys that form SDSS-V, and it consists of four telescopes optimized for broad visible-wavelength coverage of 360-980 nm feeding three fiber-fed R∼4000 spectrographs. Each telescope comprises a siderostat and an optical table that hosts powered refracting optics in a triplet configuration, hardware for image de-rotation, image acquisition and guiding systems, and a focal plane assembly. The optical design of LVM balances the science requirements for broad wavelength coverage and spaxel size with the focal ratio imposed by the spectrograph fibers and microlenses. Initial design was completed and optimized in Zemax OpticStudio software. The resulting lenses were fabricated by a vendor and assembled at Carnegie Observatories. Final testing will be on-sky at Las Campanas Observatory in Chile during commissioning in 2022. The assembly process includes bonding of the triplet lenses using Dow Corning SYLGARD 184 Silicone Elastomer (“Sylgard 184”) and mounting in a cell that travels on a motorized focusing stage on the optical table. We present details of the Sylgard 184 bonding process, a basic bonding procedure, recovery from a stress feature in two bonds, and removal of Sylgard during imperfect applications.
MICADO is the Multi-AO Imaging Camera for Deep Observations, a first light instrument for the Extremely Large Telescope (ELT). The instrument provides imaging, astrometric, spectroscopic and coronographic observing modes. MICADO will be assisted by a Single-Conjugate Adaptive Optics (SCAO) system and the Multi-conjugate Adaptive Optics RelaY (MAORY). The instrument will provide a narrow (19′′) and a wide (51′′) Field of View. MICADO can operate in the so-called stand-alone mode in the absence of MAORY with the SCAO correction alone. In this mode, the ELT focal plane is reimaged to the MICADO focal plane via the relay optics (RO). This subsystem consists of an optical bench made of carbon fiber reinforced plastic, the MICADO calibration assembly, a cover to protect all opto-mechanical components on top of the bench, and an optical assembly. The optical assembly consists of six mirrors, with diameters that go up to around 500 mm. Three of the mirrors are powered, and make a TMA. The remaining mirrors are flat motorized piston, tip-tilt mirrors for interface alignment. The nominal design provides a WFE below 25.3 nmRMS for the full FoV, and a high quality exit pupil. In this work, we present the optical design of the RO, and a comprehensive tolerance analysis. This includes alignment and manufacturing tolerances, mount-induced aberrations, warping of the RO bench, and the thermal behaviour of the complete subsystem, and looking at its effects on the WFE, and exit pupil quality. We have a compliant subsystem, which has been approved at FDR level.
METIS, the Mid-infrared E-ELT Imager and Spectrometer, is being designed for the Extremely Large Telescope (ELT) and is currently expected to arrive at the telescope early 2028. As part of the design of the instrument, we are developing the Assembly, Integration and Verification strategy for METIS. Although the sub-systems will be largely qualified at their respective institutes, only once all components come together at system level will it be possible to verify all the interfaces, full system thermal characteristics and full instrument performance. Although one of the smaller instruments for the ELT, the fully integrated METIS will still be more than 7 meters high, with a footprint in excess of 15 square meters and a weight of the order of 10 tons. This paper describes the system level assembly, integration and verification of METIS, both in Europe as well as once delivered to the telescope.
KEYWORDS: Sensors, Observatories, Telescopes, Panoramic photography, Cameras, New and emerging technologies, Temperature sensors, Electronics, Imaging systems
PANIC1 , the PAnoramic Near-Infrared Camera for the Calar Alto Observatory in Spain, was successfully commissioned in late 2014 with a mosaic of four 2K x 2K HAWAII-2RG arrays covering a field of view of approximately 30 arcmin at the 2.2 m telescope. Unfortunately, two of its science detectors suffered from extreme degradation2 along the years of operation making the instrument unsuitable for science observations. In the light of new technologies and constant innovations, it was decided to upgrade the instrument with a monolithic state of the art 4K x 4K HAWAII-4RG array. With as minimum mechanical and optical impact as possible for the instrument, the MPIA is the responsible institute for the challenging upgrade. Besides presenting the results of the initial operation of the HAWAII-4RG array in 64-Channel mode, the newly in-house designed detector mount will also be highlighted. In order to take as much advantage as possible of the new detector readout capabilities, and thanks to the modularity and flexibility of the in-house readout electronics, all 64 channels of the detector are read out in parallel. This allows for shorter integration times, which is very advantageous for a wide field imager with high background conditions.
LINC-NIRVANA at the LBT has a dual MCAO system using solely natural guide stars. A multi pyramid WFS provides the slopes to close two independent loops for ground and high layer correction, as foreseen by the Layer Oriented scheme. The projection of the deformable mirrors actuators pattern on the WFS cameras rotates, since mechanical (ground) and optical (high) derotation provides the field rotation correction needed to keep the WFS on the reference stars. We reported in the previous conferences that we succeed in obtaining valid control matrices through numerical interpolation of a few calibrated interaction matrices registered for different clocking angle. We successfully tested a different approach based on a synthetic WFS and DM model. We proved that control matrices computed by the inversion of the interaction matrices generated from the model were effectively working on the real system closing high-order correction loop on the sky, providing better performance.
The paper reports an overview of the preliminary optical design for the MICADO Relay Optics (RO) to enable early science observations of the instrument at the Extremely Large Telescope (ELT) with single-conjugate adaptive optics (SCAO). MICADO, the Multi-AO Imaging Camera for Deep Observations, is a first light imager, astrometric camera and spectrograph operating between 0.8 µm and 2.4 µm. The RO are based on a six mirror (6M) optical assembly that relays the telescope focal plane to an accessible position for the MICADO cryostat. The system includes three powered mirrors in a three-mirror-anastigmat configuration and three piston and tip- tilt flat mirrors for the alignment and the beam folding at the interfaces with the ELT and MICADO. This design represents an interesting example of optical performance optimization to achieve high performances optics both for the direct imaging channel and the pupil interface towards MICADO and the SCAO. The RO performances are analyzed and verified at a design level showing the compliance with the requirement specifications and the reliability of the design is assessed with an extended tolerance study and a minimization of the vignetting factor at the MICADO cold stop. The manuscript also contains a demonstration of the optical alignability of a 6M system in terms of pupil and focal plane steering that are essential to cope with the interface tolerances of the next generation of instrument at the foci of the extremely large telescopes.
We describe the operation of the infrared wavefront sensing based Adaptive Optics system CIAO. The Coudé Infrared Adaptive Optics (CIAO) system is a central auxiliary component of the Very Large Telescope interferometer (VLTI). It enables in particular Galactic Center observations using the GRAVITY interferometric instrument. CIAO compensates for phase disturbances caused by atmospheric turbulence, which all four 8 m Unit Telescopes (UT) experience during observation. Each of the four CIAO units generates an almost diffraction-limited image quality at its UT, which ensures that maximum flux of the observed stellar object enters the input fibers of GRAVITY. We present CIAO performance data obtained in the first 3 years of operation. We describe how CIAO is configured and used for observations with GRAVITY. We focus on the outstanding features of the infrared sensitive Saphira detector, which is used for the first time on Paranal, and show how it works as a wavefront sensor detector.
The Sloan Digital Sky Survey V (SDSS-V) is an all-sky spectroscopic survey of <6 million objects, designed to decode the history of the Milky Way, reveal the inner workings of stars, investigate the origin of solar systems, and track the growth of supermassive black holes across the Universe. The Local Volume Mapper (LVM) is one of three surveys that form SDSS-V. LVM will employ a coordinated system of four telescopes feeding three fiber spectrographs at Las Campanas Observatory in Chile. The goal is to map approximately 2500 square degrees of the Galactic plane over the wavelength range 360-980 nm with R~4000 spectral resolution. These observations will reveal for the first time how distinct gaseous environments within the Galaxy interact with each other and with the stellar population, producing the large-scale interstellar medium that we observe. Accurately mapping and calibrating a substantial portion of the sky at this spatial resolution requires a unique type of telescope system. Each of the four LVM telescopes has a diameter of 16 cm, making them considerably smaller and lighter than the instruments they feed. One telescope will host the science IFU containing ~1800 fibers arranged in a close-packed hexagon. Two additional Calibration telescopes will observe fields adjacent to the science IFU, in order to calibrate out terrestrial airglow and other geo-coronal emission. The fourth, Spectrophotometric telescope will make rapid observations of bright stars (typically 12 during a single IFU / Calibration exposure) to correct for telluric absorption lines and overall extinction. The fibers from all three types of telescope will be interspersed in the entrance slits of the spectrographs, allowing for simultaneous science and calibration exposures. Although considerably smaller than the next generation of giants, the LVM telescopes must also operate close to the limits of physical optics, and the geometry and scope of the LVM survey present unique challenges. For example, with this type of telescope at the Las Campanas site, the effects of optical aberrations, diffraction, seeing, and (uncorrected) atmospheric dispersion are all of comparable scale. This, coupled with the need for repeated and reliable measurements over years, leads to some unconventional design choices. This paper presents the preliminary design of the LVM telescope system and discusses the requirements and tradeoffs that led to the baseline choices.
MICADO is the Multi-AO Imaging Camera for Deep Observations, a first light instrument for the Extremely Large Telescope (ELT). The instrument provides imaging, astrometric, spectroscopic and coronographic observing modes. MICADO will be assisted by a Single-Conjugate Adaptive Optics (SCAO) system and the Multi-conjugate Adaptive Optics RelaY (MAORY). The instrument will provide a narrow (19′′) and a wide (51”) Field of View. MICADO can operate in the so-called stand-alone mode in the absence of MAORY with the SCAO correction alone. Here, we present the opto-mechanical design of the Relay Optics (RO), the optical system relaying the ELT focal plane to an accessible position for MICADO using the SCAO-only stand-alone observing mode. The RO consists of an optical bench made of carbon fiber reinforced plastic (CFRP), an optical assembly made of three flat mirrors with motorized piston-tip-tilt mounts and three additional powered mirrors of up to ~500 mm in diameter, the MICADO calibration assembly, and a cover to protect all opto-mechanical components on top of the bench. A 9-point whiffletree support, combined with a thermal compensation system is implemented for the critical mirrors. The static and the dynamic performance of the MICADO RO are investigated through a detailed Finite Element Model (FEM), the results are combined with a Zernike basis representation of the mirror surface deformations performed in Zemax for assessing the optical performance.
MICADO will enable the ELT to perform diffraction limited near-infrared observations at first light. The instrument’s capabilities focus on imaging (including astrometric and high contrast) as well as single object spectroscopy. This contribution looks at how requirements from the observing modes have driven the instrument design and functionality. Using examples from specific science cases, and making use of the data simulation tool, an outline is presented of what we can expect the instrument to achieve.
The paper describes the preliminary design of the MICADO calibration assembly. MICADO, the Multi-AO Imaging CAmera for Deep Observations, is targeted to be one of the first light instruments of the Extremely Large Telescope (ELT) and it will embrace imaging, spectroscopic and astrometric capabilities including their calibration. The astrometric requirements are particularly ambitious aiming for ~ 50 μas differential precision within and between single epochs. The MICADO Calibration Assembly (MCA) shall deliver flat-field, wavelength and astrometric calibration and it will support the instrument alignment to the Single-Conjugate Adaptive Optics wavefront sensor. After a complete overview of the MCA subsystems, their functionalities, design and status, we will concentrate on the ongoing prototype testing of the most challenging components. Particular emphasis is put on the development and test of the Warm Astrometric Mask (WAM) for the calibration of the optical distortions within MICADO and MAORY, the multiconjugate AO module.
We present the preliminary optical design of METIS, the Mid-infrared E-ELT Imager and Spectrograph, and study the end-to-end performance regarding wavefront errors and non-common path aberrations. We discuss the results of the Monte Carlo simulations that contain the manufacturing and alignment errors of the opto-mechanical system. We elaborate on the wavefront error budget of the instrument detailing all contributors. We investigate the mid and high spatial frequency errors of the optical surfaces, which we model using simulated surface height errors maps of one dimensional Power Spectral Density (PSD) functions.
This paper reports on early commissioning of LINC-NIRVANA (LN), an innovative Multi-Conjugate Adaptive Optics (MCAO) system for the Large Binocular Telescope (LBT). LN uses two, parallel MCAO systems, each of which corrects turbulence at two atmospheric layers, to deliver near diffraction-limited imagery over a two-arcminute field of view. We summarize LN’s approach to MCAO and give an update on commissioning, including the achievement of First Light in April 2018. This is followed by a discussion of challenges that arise from our particular type of MCAO and the solutions implemented. We conclude with a brief look forward to the remainder of commissioning and future upgrades.
METIS is the Mid-infrared Extremely large Telescope Imager and Spectrograph, one of the first generation instruments of ESO’s 39m ELT. All scientific observing modes of METIS require adaptive optics (AO) correction close to the diffraction limit. Demanding constraints are introduced by the foreseen coronagraphy modes, which require highest angular resolution and PSF stability. Further design drivers for METIS and its AO system are imposed by the wavelength regime: observations in the thermal infrared require an elaborate thermal, baffling and masking concept. METIS will be equipped with a Single-Conjugate Adaptive Optics (SCAO) system. An integral part of the instrument is the SCAO module. It will host a pyramid type wavefront sensor, operating in the near-IR and located inside the cryogenic environment of the METIS instrument. The wavefront control loop as well as secondary control tasks will be realized within the AO Control System, as part of the instrument. Its main actuators will be the adaptive quaternary mirror and the field stabilization mirror of the ELT. In this paper we report on the phase B design work for the METIS SCAO system; the opto-mechanical design of the SCAO module as well as the control loop concepts and analyses. Simulations were carried out to address a number of important aspects, such as the impact of the fragmented pupil of the ELT on wavefront reconstruction. The trade-off that led to the decision for a pyramid wavefront sensor will be explained, as well as the additional control tasks such as pupil stabilization and compensation of non-common path aberrations.
This paper reports on the installation and initial commissioning of LINC-NIRVANA (LN), an innovative high resolution, near-infrared imager for the Large Binocular Telescope (LBT). We present the delicate and difficult installation procedure, the culmination of a re-integration campaign that was in full swing at the last SPIE meeting. We also provide an update on the ongoing commissioning campaigns, including our recent achievement of First Light. Finally, we discuss lessons learned from the shipment and installation of a large complex instrument.
LINC-NIRVANA is an innovative, high-resolution, near-infrared imager for the Large Binocular Telescope. Its Multi-Conjugate Adaptive Optics system uses natural guide-stars and the layer-oriented, multiple-field of view approach for high sky coverage and eventual interferometric beam combination. We describe LINC-NIRVANA’s particular flavour of MCAO and its associated challenges, and report on final lab integration and system level testing. LINC-NIRVANA is currently at the telescope undergoing final alignment and tests before First Light late this fall.
LINC-NIRVANA is an innovative, high-resolution near-infrared imager for the Large Binocular Telescope. Its Multi- Conjugate Adaptive Optics system uses natural guide-stars and provides high sky coverage for single-eye, binocular, and eventually, interferometric observations. We report on final lab integration and system level testing, as well as technical and logistical challenges of shipping and installing a large, delicate, complex instrument. LINC-NIRVANA is currently at LBT undergoing final alignment and tests before First Light late this fall. Managing the transition to operations involves the interactions between telescope alignment and calibration, commissioning of the instrument, and executing the Early Science plan.
MICADO will equip the E-ELT with a first light capability for diffraction limited imaging at near-infrared wavelengths. The instrument’s observing modes focus on various flavours of imaging, including astrometric, high contrast, and time resolved. There is also a single object spectroscopic mode optimised for wavelength coverage at moderately high resolution. This contribution provides an overview of the key functionality of the instrument, outlining the scientific rationale for its observing modes. The interface between MICADO and the adaptive optics system MAORY that feeds it is summarised. The design of the instrument is discussed, focusing on the optics and mechanisms inside the cryostat, together with a brief overview of the other key sub-systems.
The LBT (Large Binocular Telescope), located at about 3200m on Mount Graham (Tucson, Arizona) is an innovative project undertaken by institutions from Europe and USA. LINC-NIRVANA is an instrument which provides MCAO (Multi-Conjugate Adaptive Optics) and interferometry, combining the light from the two 8.4m telescopes coherently. This configuration offers 23m-baseline optical resolution and the sensitivity of a 12m mirror, with a 2 arc-minute diffraction limited field of view. The integration, alignment and testing of such a big instrument requires a well-organized choreography and AIV planning which has been developed in a hierarchical way. The instrument is divided in largely independent systems, and all of them consist of various subsystems. Every subsystem integration ends with a verification test and an acceptance procedure. When a certain number of systems are finished and accepted, the instrument AIV phase starts. This hierarchical approach allows testing at early stages with simple setups. The philosophy is to have internally aligned subsystems to be integrated in the instrument optical path, and extrapolate to finally align the instrument to the Gregorian bent foci of the telescope. The alignment plan was successfully executed in Heidelberg at MPIA facilities, and now the instrument is being re-integrated at the LBT over a series of 11 campaigns along the year 2016. After its commissioning, the instrument will offer MCAO sensing with the LBT telescope. The interferometric mode will be implemented in a future update of the instrument. This paper focuses on the alignment done in the clean room at the LBT facilities for the collimator, camera, and High-layer Wavefront Sensor (HWS) during March and April 2016. It also summarizes the previous work done in preparation for shipping and arrival of the instrument to the telescope. Results are presented for every step, and a final section outlines the future work to be done in next runs until its final commissioning.
The paper describes the developments towards an end-to-end optical model based on a commercial ray tracing software for studying the effects of the telescope and instrumental instabilities on the Multi-AO Imaging Camera for Deep Observations (MICADO). The primary goal and observing mode of MICADO is imaging, with a focus on relative astrometry with an accuracy of about 50 μas. To achieve this ambitious goal a careful examination of the possible random and systematic effects that can influence the astrometric accuracy is required. Here we concentrate on the perturbations coming from the different telescope and instrumental instabilities, mainly related to the static and dynamical perturbations of the European-Extremely Large Telescope (E-ELT) optics, the cold optics tolerances of the instrument and the intrinsic geometric distortions of both the systems. ESO developed an extended dataset of the E-ELT perturbations that are integrated inside the optical model of the telescope and the instrument relay optics for gathering the aberrated wavefronts. The wavefront error residuals are then propagated inside the system to check the distortions and their effects on the astrometric measurement at the instrument focal plane. From our analysis the dominating instrumental errors are: (i) the telescope induced distortions, in the order of => 100μas, that originate from the optics misalignments and presumably vary over <= 1hr time-scales, and must be calibrated against sky measurements; (ii) the instrument optics induced distortions that can reach ∼ 1 arcsec levels, but are more stable than the telescope perturbations. They will be calibrated with the use of an astrometric calibration mask. We derived the order of magnitude of the astrometric distortions of E-ELT and MICADO. The results of our study will help to define an efficient instrumental calibration strategy against the astrometric error of the instrument.
The delivered image quality of ground-based telescopes depends greatly on atmospheric turbulence. At every observatory, the majority of the turbulence (up to 60-80% of the total) occurs in the ground layer of the atmosphere, that is, the first few hundred meters above the telescope pupil. Correction of these perturbations can, therefore, greatly increase the quality of the image. We use Ground-layer Wavefront Sensors (GWSs) to sense the ground layer turbulence for the LINC-NIRVANA (LN) instrument, which is in its final integration phase before shipment to the Large Binocular Telescope (LBT) on Mt. Graham in Arizona.19 LN is an infrared Fizeau interferometer, equipped with an advanced Multi-Conjugate Adaptive Optics (MCAO) module, capable of delivering images with a spatial resolution equivalent to that of a ~23m diameter telescope. It exploits the Layer-Oriented, Multiple Field of View, MCAO approach3 and uses only natural guide stars for the correction. The GWS has more than 100 degrees of freedom. There are opto-mechanical complexities at the level of sub- systems, the GWS as a whole, and at the interface with the telescope. Also, there is a very stringent requirement on the superposition of the pupils on the detector. All these conditions make the alignment of the GWS very demanding and crucial. In this paper, we discuss the alignment and integration of the left-eye GWS of LN and detail the various tests done in the lab at INAF-Padova to verify proper system operation and performance.
LINC-NIRVANA is an instrument combining the two 8.4 m telescopes of the Large Binocular Telescope (LBT)
coherently, in order to achieve the optical resolution of the 23 meter baseline. For this interferometric instrument
concept, the common beam combination requires diffraction limited optical performance. The optics, realized as a
Cassegrain telescope design, consists of aluminum mirrors, designed and manufactured to fulfill the challenging
specifications required for interferometric imaging. Due to the science wavelength range from 1 μm to 2.4 μm, covering
the J, H and K band of the atmosphere, the complete beam combiner including the optics is operated in cryogenic
environment at 60 Kelvin. Here, we demonstrate the verification of the optical performance at this temperature for
classical in-coherent and coherent illumination. We outline the test setup and present the achieved results of wavefront
error for the individual beams and fringe contrast for the interferometric point spread function.
This paper continues the already presented integration of the interferometric camera with the focus on the performance
of the cryogenic optics.
PANIC is the new PAnoramic Near-Infrared camera for Calar Alto, a joint project by the MPIA in Heidelberg, Germany,
and the IAA in Granada, Spain. It can be operated at the 2.2m or 3.5m CAHA telescopes to observe a field of view of
30'x30' or 15'x15' respectively, with a sampling of 4096x4096 pixels. It is designed for the spectral bands from Z to K,
and can be equipped with additional narrow-band filters.
The instrument is close to completion and will be delivered to the observatory in Spain in fall 2014. It is currently in the
last stage of assembly, where the optical elements are being aligned, which will be followed by final laboratory tests of
the instrument. This paper contains an update of the recent progress and shows results from the optical alignment and
detector performance tests.
The LBT (Large Binocular Telescope) located in Mount Graham near Tucson/Arizona at an altitude of about
3200m, is an innovative project being undertaken by institutions from Europe and USA. The structure of the
telescope incorporates two 8.4-meter telescopes on a 14.4 center-to-center common mount. This configuration
provides the equivalent collecting area of a 12m single-dish telescope.
LINC-NIRVANA is an instrument to combine the light from both LBT primary mirrors in an imaging Fizeau
interferometer. Many requirements must be fulfilled in order to get a good interferometric combination of the
beams, being among the most important plane wavefronts, parallel input beams, homotheticity and zero optical path
difference (OPD) required for interferometry. The philosophy is to have an internally aligned instrument first, and
then align the telescope to match the instrument.
The sum of different subsystems leads to a quite ambitious system, which requires a well-defined strategy for
alignment and testing. In this paper I introduce and describe the followed strategy, as well as the different solutions,
procedures and tools used during integration. Results are presented at every step.
LINC-NIRVANA (LN) is the near-infrared, Fizeau-type imaging interferometer for the large binocular telescope (LBT) on Mt. Graham, Arizona (elevation of 3267 m). The instrument is currently being built by a consortium of German and Italian institutes under the leadership of the Max Planck Institute for Astronomy in Heidelberg, Germany. It will combine the radiation from both 8.4 m primary mirrors of LBT in such a way that the sensitivity of a 11.9 m telescope and the spatial resolution of a 22.8 m telescope will be obtained within a 10.5×10.5 arcsec 2 scientific field of view. Interferometric fringes of the combined beams are tracked in an oval field with diameters of 1 and 1.5 arcmin. In addition, both incoming beams are individually corrected by LN’s multiconjugate adaptive optics system to reduce atmospheric image distortion over a circular field of up to 6 arcmin in diameter. A comprehensive technical overview of the instrument is presented, comprising the detailed design of LN’s four major systems for interferometric imaging and fringe tracking, both in the near infrared range of 1 to 2.4 μm, as well as atmospheric turbulence correction at two altitudes, both in the visible range of 0.6 to 0.9 μm. The resulting performance capabilities and a short outlook of some of the major science goals will be presented. In addition, the roadmap for the related assembly, integration, and verification process are discussed. To avoid late interface-related risks, strategies for early hardware as well as software interactions with the telescope have been elaborated. The goal is to ship LN to the LBT in 2014.
LINC-NIRVANA (LN) is the near-infrared, Fizeau-type imaging interferometer for the Large Binocular Telescope
(LBT) on Mt. Graham, Arizona, USA (3267m of elevation). The instrument is currently being built by a consortium of
German and Italian institutes under the leadership of the Max Planck Institute for Astronomy (MPIA) in Heidelberg,
Germany. It will combine the radiation from both 8.4m primary mirrors of LBT in such a way that the sensitivity of a
11.9m telescope and the spatial resolution of a 22.8m telescope will be obtained within a 10.5arcsec x 10.5arcsec
scientific field of view. Interferometric fringes of the combined beams are tracked in an oval field with diameters of 1
and 1.5arcmin. In addition, both incoming beams are individually corrected by LN’s multi-conjugate adaptive optics
(MCAO) system to reduce atmospheric image distortion over a circular field of up to 6arcmin in diameter.
This paper gives a comprehensive technical overview of the instrument comprising the detailed design of LN’s four
major systems for interferometric imaging and fringe tracking, both in the NIR range of 1 - 2.4μm, as well as
atmospheric turbulence correction at two altitudes, both in the visible range of 0.6 - 0.9μm. The resulting performance
capabilities and a short outlook of some of the major science goals will be presented. In addition, the roadmap for the
related assembly, integration and verification (AIV) process will be discussed. To avoid late interface-related risks,
strategies for early hardware as well as software interactions with the telescope have been elaborated. The goal is to ship
LN to the LBT in 2014.
In order to achieve high sky coverage with natural guide star adaptive optics systems, the reference stars need to be
chosen over a large field of view. But the size of the optical beam can become unmanageably large in current and
planned future giant telescopes. This can render the optics unaffordable. To solve this issue, we have adopted two
approaches - multiple fields of view and star-enlargers - for the LINC-NIRVANA layer-oriented, multiple-conjugated
adaptive optics system. In this paper, we compare and contrast the advantages and disadvantages of various optical
configurations for wide-field, natural guide star acquisition on current 8-meter and future 25-40 meter extremely large
telescopes.
LINC-NIRVANA is an interferometric imaging camera, which combines the two 8.4 m telescopes of the Large
Binocular Telescope (LBT). The instrument operates in the wavelength range from 1.1 μm to 2.4 μm, covering the J, H
and K-band, respectively. The beam combining camera (NIRCS) offers the possibility to achieve diffraction limited
images with the special resolution of a 23 m telescope. The optics are designed to deliver a 10 arcsec × 10 arcsec field of
view with 5 mas resolution. In this paper we describe the evolution of the cryogenic optics, from design and
manufacturing to verification. Including the argumentation for decisions we made in order to present a sort of guideline
for large cryo-optics. We also present the alignment and testing strategies at a detailed level.
LINC-NIRVANA (LN) is a near-infrared image-plane beam combiner with advanced, multi-conjugated adaptive optics
for the Large Binocular Telescope. Non-common path aberrations (NCPAs) between the near-infrared science camera
and the wave-front sensor (WFS) are unseen by the WFS and therefore are not corrected in closed loop. This would
prevent LN from achieving its ultimate performance. We use a modified phase diversity technique to measure the
internal optical static aberrations and hence the NCPAs. Phase diversity is a methodology for estimating wave-front
aberrations by solving an unconstrained optimization problem from multiple images whose pupil phases differ from one another by a known amount. We conduct computer simulations of the reconstruction of aberrations of an optical system with the phase diversity method. In the reconstruction, we fit the wave-front to Zernike polynomials to reduce the number of variables. The limited-memory Broyden-Fletcher-Goldfarb-Shanno (L-BFGS) algorithm is very well suited to phase diversity (PD) due to its good performance in solving large scale optimization problems. The main constraint for the implementation of PD for LN is that we cannot add extra components to the internal interferometric camera imaging system to obtain infocus and defocus images. In this paper, we introduce a new method, namely shifting the focal plane source, not the detector, to overcome this constraint. Some experiments were done to test and verify this method and the results are presented and discussed. The study shows that the method is very flexible and the paper gives practical guidelines for the application of phase diversity methods to characterize adaptive optics systems.
Even though the last instruments built with the previous generation of MPIA-ROE are offering in the meantime most of
the standard readout modes, the current generation ROE is based on the experience of the last years, and besides other
properties like small volume, more channels, less power consumption, etc., it will also allow extended readout modes in
the near future by using the detector engineering and data interfaces of GEIRS.
The Hawaii-2-RG detector has a large amount of operational flexibilities to support extended readout modes. With
special properties in the pattern generator of the ROE and in GEIRS, new extended readout modes can be implemented
identically for the Hawaii-2 and the Hawaii-2RG in multichannel mode.
This paper presents an overview of the standard readout schemes and describes additional selectable options, offered
idle-modes, and some new extended modes available with this generation of MPIA-ROE for the next instruments and
instrument updates using HgCdTe-detectors.
During the last 15 years MPIA has built 8 sets of previous readout electronics (ROE) for 8 astronomical infrared
instruments1-8. The generic infrared camera software GEIRS (spoken like 'cheers') is used in these instruments either as a
pure readout software layer or as an overall control software for IR-instruments, the last case in particular with
instruments for the Calar-Alto observatory in Spain.
PANIC is developed at MPIA, Heidelberg, Germany and IAA, Granada, Spain. This instrument will cover a field of
view of 0.5x0.5 degrees at the 2.2m telescope in the spectral bands Z to K. All hardware has been manufactured, the
instrument is currently assembled and tested. In this contribution we describe results of some tests.
One possible key reference element in optical alignment is represented by the rotational stage, a mechanical bearing, or
any similar suitable device having enough accuracy and precision so that optical tolerances are reasonably relaxed wrt
imperfections in the rotational movement. This allows a safe, reliable, easy to reproduce, determination of both rays
parallel to the axis or to their centering within almost any plane. An image derotator, that in its simplest form is made up
by three flat mirrors arranged in a so called K-mirror layout, moving together on a precision rotating stage, seems to be
the most safe, strong, and self built-in alignment tool. Moreover you can use the mechanical part as well as the optical
one. Care has to be given when internally and externally aligning has to be accomplished within a certain degree of
precision. To further make the situation more complex, the technical overall requirements can be tight enough that the
distribution of the error budget among the various components (imperfect mechanical rotation, imperfect internal
alignment, flexures during rotations) is not due to a single item. In this case, in fact, a number of tips and tricks can be
useful to find out which is the best approach to follow. The specific case of the two K-mirrors on board LINCNIRVANA
is here illustrated in a few lessons.
LINC-NIRVANA is an instrument to combine the light from both LBT primary mirrors in an imaging Fizeau interferometer. The goals in terms of resolution and field of view are quite ambitious, which leads to a complex instrument consisting of a bunch of subsystems. The layer oriented MCAO system alone is already quite complicated and to get everything working together properly is not a small challenge. As we are reaching the completion of LINC-NIRVANA's subsystems, it becomes more and more important to define a strategy to align all these various subsystems. The specific layout of LINC-NIRVANA imposes some restrictions and difficulties on the sequence and the method of this alignment. The main problem for example is that we have to get two perfectly symmetrical focal planes to be able to properly combine them interferometrically. This is the major step on which all further alignment is based on, since all the subsystems (collimator and camera optics, wavefront sensors, cold IR optics, etc.) rely on these focal planes as a reference. I will give a small introduction on the optics of the instrument and line out the resulting difficulties as well as the strategy that we want to apply in order to overcome these.
LINC-NIRVANA is an interferometric imaging camera, which combines the two 8.4 m telescopes of the Large
Binocular Telescope (LBT). The instrument operates in the wavelength range from 1.1 μm to 2.4 μm, covering the J, H and K-bands. The beam combining camera (NIRCS) offers the possibility to achieve diffraction limited images with the
spatial resolution of a 23 m telescope.
This camera, which combines the AO corrected beams of both telescopes, is designed to deliver a 10 arcsec x 10 arcsec
diffraction limited field of view. The optics and cryo-mechanics are designed for operation at 60 Kelvin. Equipped with a
HAWAII-2 detector mounted on a rotation stage in order to compensate for the sky rotation, a filter wheel and a dichroic
wheel to split the light into the science channel and the fringe tracking channel, the camera is fairly large and complex
and requires certain features to be considered and tested.
The verification of all these components follows a challenging AIV plan. We describe this AIV phase from initial
integration of individual units to the final verification tests of the complete system. We report the performance of the
cryogenic opto-mechanics and of the science detector. We also demonstrate the functionality of the cryo-mechanics and
the cryo-cooling at sub-system level, which represents the current state of integration. Finally, we discuss key elements
of our design and potential pros and cons.
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.
LINC-NIRVANA is a near infrared interferometric imager with a pair of layer-oriented multi-conjugate adaptive
optics systems (ground layer and high layer) for the Large Binocular Telescope. To prepare for the commissioning
of LINC-NIRVANA, we have integrated the high layer wavefront sensor and its associated deformable mirror (a
Xinetics-349) in a laboratory, located at Max Planck Institute for Astronomy, in Heidelberg, Germany. Together
with a telescope simulator, which includes a rotating field and phase screens that introduce the effects of the
atmosphere, we tested the acquisition of multiple guide stars, calibrating the system with the push-pull method,
and characterizing the wavefront sensor together with the deformable mirror. We have closed the AO loop with
up to 200 Zernike modes and with multiple guide stars. The AO correction demonstrated that uniform correction
can be achieved in a large field of view. We report the current status and results of the experiment.
LINC-NIRVANA is the Fizeau beam combiner for the LBT, with the aim to retrieve the sensitivity of a 12m telescope
and the spatial resolution of a 22.8m one. Despite being only one of the four wavefront sensors of a layer-oriented
MCAO system, the GWS, which is retrieving the deformation introduced by the lower atmosphere, known to be the main
aberration source, reveals a noticeable internal opto-mechanical complexity.
The presence of 12 small devices used to select up to the same number of NGSs, with 3 optical components each,
moving in a wide annular 2'-6' arcmin Field of View and sending the light to a common pupil re-imager, and the need to
obtain and keep a very good super-imposition of the pupil images on the CCD camera, led to an overall alignment
procedure in which more than a hundred of degrees of freedom have to be contemporary adjusted.
The rotation of the entire WFS to compensate for the sky movement, moreover, introduces a further difficulty both in the
alignment and in ensuring the required pupil superposition stability.
A detailed description of the alignment procedure is presented here, together with the lessons learned managing the
complexity of such a WFS, which led to considerations regarding future instruments, like a possible review of numerical
versus optical co-add approach, above all if close to zero read-out noise detectors will be soon available.
Nevertheless, the GWS AIV has been carried out and the system will be soon mounted at LBT to perform what is called
the Pathfinder experiment, which consists in ground-layer correction, taking advantage of the Adaptive Secondary
deformable Mirror.
We present two designs of a filter mounting structure for the Near-Infrared Imaging Photometer (NIP) planned
for the Euclid dark energy space mission. The three large near-infrared filters - with a 127 mm diameter, 12 mm
thickness and a 330 g mass per element - are challenging to mount. We present the design considerations,
finite element analysis and results from the first prototyping campaign of these structures. The rationale behind
the down-selection between the two designs is detailed and we conclude with recommendations on future
developments of mounts of this type. The results presented here are based on work performed during the Euclid
Assessment Study.
The Euclid dark energy mission is currently competing in ESA's Cosmic Vision program. Its imaging instrument,
which has one visible and one infrared channel, will survey the entire extragalactic sky during the 5 year mission.
The near-infrared imaging photometer (NIP) channel, operating in the ~0.92 - 2.0 μm spectral range, will be
used in conjunction with the visible imaging channel (VIS) to constrain the nature of dark energy and dark
matter. To meet the stringent overall photometric requirement, the NIP channel requires a dedicated on-board
flat-field source to calibrate the large, 18 detector focal plane.
In the baseline concept a 170 mm Spectralon diffuser plate, mounted to a pre-existing shutter mechanism
outside the channel, is used as a flat-field calibration target, negating the need for an additional single-point-failure
mechanism. The 117 × 230 mm focal plane will therefore be illuminated through all of the channel's
optical elements and will allow flat-field measurements to be taken in all wavelength bands. A ring of low power
tungsten lamps, with custom reflecting elements optimized for optical performance, will be used to illuminate
the diffuser plate.
This paper details the end-to-end optical simulations of this concept, a potential mechanical implementation
and the initial tests of the proposed key components.
LINC-NIRVANA[1] (LN) is an instrument for the Large Binocular Telescope[2] (LBT). Its purpose is to combine the light
coming from the two primary mirrors in a Fizeau-type interferometer. In order to compensate turbulence-induced
dynamic aberrations, the layer oriented adaptive optics system of LN[3] consists of two major subsystems for each side:
the Ground-Layer-Wavefront sensor (GLWS) and the Mid- and High-Layer Wavefront sensor (MHLWS). The MHLWS
is currently set up in a laboratory at the Max-Planck-Institute for Astronomy in Heidelberg. To test the multi-conjugate
AO with multiple simulated stars in the laboratory and to develop the necessary control software, a dedicated light
source is needed. For this reason, we designed an optical system, operating in visible as well as in infrared light, which
imitates the telescope's optical train (f-ratio, pupil position and size, field curvature). By inserting rotating surface etched
glass phase screens, artificial aberrations corresponding to the atmospheric turbulence are introduced. In addition,
different turbulence altitudes can be simulated depending on the position of these screens along the optical axis. In this
way, it is possible to comprehensively test the complete system, including electronics and software, in the laboratory
before integration into the final LINC-NIRVANA setup. Combined with an atmospheric piston simulator, also this effect
can be taken into account. Since we are building two identical sets, it is possible to feed the complete instrument with
light for the interferometric combination during the assembly phase in the integration laboratory.
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
layer-oriented MCAO systems (one for each arm of the interferometer) are conjugated to the ground layer and
an additional layer in the upper atmosphere. In this contribution MCAO wavefront control is discussed in the
context of the overall control scheme for LINC-NIRVANA. Special attention is paid to a set of auxiliary control
tasks which are mandatory for MCAO operation: The Fields of View of each wavefront sensor in the instrument
have to be derotated independent from each other and independently from the science field. Any wavefront
information obtained by the sensors has to be matched to the time invariant modes of the deformable mirrors
in the system. The tip/tilt control scheme is outlined, in which atmospheric, but also instrumental tip/tilt
corrections are sensed with the high layer wavefront sensor and corrected by the adaptive secondary mirror of
the LBT. Slow image motion effects on the science detector have to be considered, which are caused by flexure
in the non-common path between AO and the science camera, atmospheric differential refraction, and alignment
tolerances of the derotators. Last but not least: The sensor optics (pyramids) have to be accurately positioned
at the images of natural reference stars.
The LINC-NIRVANA wavefront sensors are in their AIT phase. The first Ground-layerWavefront Sensor (GWS)
is shaping in the Adaptive Optics laboratory of the Astronomical Observatory of Padova, while both the Mid-
High Wavefront Sensors (MHWSs) have been aligned and tested as stand-alone units in the Observatory of
Bologna (MHWS#1 aligned to LINC-NIRVANA post focal relay optics).
LINC-NIRVANA is a Fizeau infrared interferometer equipped with advanced, MultiConjugated Adaptive
Optics (MCAO) for the Large Binocular Telescope. The aim of the instrument is to allow true interferometric
imagery over a 10" square Field of View (FoV), getting the sensitivity of a 12m telescope and the spatial resolution
of a 22.8m one. Thanks to the MCAO concept, LINC-NIRVANA will use up to 20 Natural Guide Stars (NGS)
which are divided, according to Layer-Oriented Multiple Field of View technique, between the GWSs and the
MHWSs. To find such a large number of references, the AO systems will use a wide FoV of 6' in diameter and
the light coming from the references used by each WFS will optically sum on its CCD camera.
The MHWSs will detect the deformations due to the high layers and will select up to 8 NGSs in the inner 2'
FoV.
The GWSs, instead, will reconstruct the deformations introduced by the lower atmosphere, which was found
out to be the main source of seeing. Their peculiarity is the highest number of references (up to 12) ever used
in a single instrument, selected in an annular 2'-6' FoV.
The atmospheric piston simulator is an integral part of the calibration unit of LINC-NIRVANA, the Fizeau
interferometric imager for the Large Binocular Telescope. The calibration unit will be necessary to align and set
up the different opto - mechanical subsystems of the instrument. It will assist in (1) the alignment of the optics
via reference fibers; (2) establishing zero optical path difference using a balanced fiber splitter; (3) flat fielding of
the detectors with an integrating sphere; (4) correction of the non-common path aberrations using a fiber-based
phase diversity source; and (5) calibration of the adaptive optics with a rotating reference fiber plate. Substantial
testing and verification of the fringe tracker under as realistic as possible conditions in the lab is desirable, since
the performance of the fringe tracker will ultimately determine the high angular resolution imaging capability
of LINC-NIRVANA as a whole. We are therefore also constructing an atmospheric piston simulator working in
the J and H photometric bands. As with many of the other calibration unit sub-systems, our design concept
is mainly fiber based. Opto - electronic phase modulators will be used to introduce the piston sequences. The
control system of the piston modulators will allow for easy implementation of different vibration power spectra.
This will enable us to test and demonstrate the capabilities of the fringe tracker under realistic conditions.
PANIC, the PAnoramic Near-Infrared Camera for Calar Alto, is one of the next generation instruments for this
observatory. In order to cover a field of view of approximately 30 arcmin, PANIC uses a mosaic of four 2k x 2k
HAWAII-2RG arrays from Teledyne. This document presents the preliminary results of the basic characterization of the
mosaic. The performance of the system as a whole, as well as the in-house readout electronics and software capabilities
will also be briefly discussed.
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.
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.
PRIMA, the instrument for Phase-Referenced Imaging and Micro-arcsecond Astrometry at the VLTI, is currently being
developed at ESO. PRIMA will implement the dual-feed capability, at first for two UTs or ATs, to enable simultaneous
interferometric observations of two objects that are separated by up to 1 arcmin. PRIMA is designed to perform narrow-angle
astrometry in K-band with two ATs as well as phase-referenced aperture synthesis imaging with instruments like
Amber and Midi. In order to speed up the full implementation of the 10 microarcsec astrometric capability of the VLTI
and to carry out a large astrometric planet search program, a consortium lead by the Observatoire de Genève, Max
Planck Institute for Astronomy, and Landessternwarte Heidelberg, has built Differential Delay Lines for PRIMA and is
developing the astrometric observation preparation and data reduction software. When the facility becomes fully
operational in 2009, we will use PRIMA to carry out a systematic astrometric Exoplanet Search program, called ESPRI.
In this paper, we describe the narrow-angle astrometry measurement principle, give an overview of the ongoing hardand
software developments, and outline our anticipated astrometric exoplanet search program.
ESPRI is a project which aims at searching for and characterizing extra-solar planets by dual-beam astrometry with
PRIMA@VLTI. Differential Delay Lines (DDL) are fundamental for achieving the micro-arcseconds accuracy required
by the scientific objective. Our Consortium, consisting of the Geneva Observatory, the Max-Planck Institut for
Astronomy Heidelberg, and the Landessternwarte Heidelberg, in collaboration with ESO, has built and tested these
DDLs successfully and will install them in summer 2008 at the VLTI. These DDLs consist of high quality cat's eyes
displaced on a parallel beam-mechanics and by means of a two-stage actuation with a precision of 5 nm over a stroke
length of 70 mm. Over the full range, a bandwidth of about 400 Hz is achieved. The DDLs are operated in vacuum. We
shall present, in this paper, their design and their exceptional performances.
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.
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.
The last step in designing and building instruments are the verification and acceptance tests of the assembled units and of
the final instrument. For instruments, which are engineered to work at the limit of feasibility, these tests must be accurate
and stable at a level much better than the expected performance of the instrument. Particularly for interferometric
instruments, this requires special care for the test planning and implementation in order to achieve the necessary
performance. This paper describes the verification and acceptance tests of the PRIMA DDL optics in terms of wavefront
error and tilt requirements as well as the assembling and aligning accuracy. We demonstrate the conformity of the optics
and point out the limitations of the test methods.
In this paper we present an overview of the construction and implementation of the unmodulated infrared pyramid wavefront sensor PYRAMIR at the Calar Alto 3.5 m telescope. PYRAMIR is an extension of the existing visible Shack-Hartmann adaptive optics system ALFA, which allows wavefront sensing in the near-infrared wavefront regime. We describe the optical setup and the calibration procedure of the pyramid wavefront sensor. We discuss possible drawbacks of the calibration and show the results gained on Calar Alto.
The MPIA is leading an international consortium of institutes building an instrument called LINC-NIRVANA. The instrument will combine the light from the two 8.4 m primary mirrors of the LBT. The beam combiner will operate at wavelengths between 1.1 and 2.4 microns, using a Hawaii2 detector. A volume of about 1.6 m high with a diameter of about 0.65 m is required for the cold optics. The size of the instrument and the high requirements on vibrations brought us to a new approach for the cooling of the cryostat, which has never been tried in astronomy. The cryostat will be cooled by a flow of Helium gas. The cooler which cools the gas will be placed far away on a different level in the telescope building. The cold helium will be fed through long vacuum isolated transfer lines to the instrument cryostat. Inside the cryostat a tube will be wrapped around the mounting structure of the cold optics. The first hardware arrived at the MPIA in 2005 and the system will soon be tested in our labs.
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.
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.
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.
This paper describes the whole process of designing, manufacturing and assembling the optics for an infrared pyramid wavefront sensor, called PYRAMIR. This sensor is built to work with the adaptive optical system at the 3.5 m telescope of the Calar Alto Observatory, Spain, which controls a 97 actuator deformable mirror. PYRAMIR is working in combination with an infrared science camera, which is used for observations. Since the wavefront sensor works in the near infrared (1.0 μm to 2.4 μm), the detector, the optics and all the mechanics are cooled to liquid nitrogen temperature. For this cryogenic condition, special care has to be taken for the optical design and the mounting of the lenses. We describe in detail the process from infrared optical design and cryo-mechanical engineering, to the final assembly of the opto-mechanical units and testing in the lab. Technical solutions are illustrated and the final performance is demonstrated.
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.
A new wavefront sensor based on the pyramid principle is being built at MPIA, with the objective of integration in the Calar Alto adaptive optics system ALFA. This sensor will work in the near-infrared wavelength range (J, H and K bands). We present here an update of this project, named PYRAMIR, which will have its first light in some months. Along with the description of the optical design, we discuss issues like the image quality and chromatic effects due to band sensing. We will show the characterization of the tested pyramidal components as well as refer to the difficulties found in the manufacturing process to meet our requirements. Most of the PYRAMIR instrument parts are kept inside a liquid nitrogen cooled vacuum dewar to reduce thermic radiation. The mechanical design of the cold parts is described here. To gain experience, a laboratory pyramid wavefront sensor was set up, with its optical design adapted to PYRAMIR. Different tests were already performed. The electronic and control systems were designed to integrate in the existing ALFA system. We give a description of the new components. An update on the future work is presented.
The PRIMA facility will implement dual-star astrometry at the VLTI. We have formed a consortium that will build the PRIMA differential delay lines, develop an astrometric operation and calibration plan, and deliver astrometric data reduction software. This will enable astrometric planet surveys with a target precision of 10μas. Our scientific goals include determining orbital inclinations and masses for planets already known from radial-velocity surveys, searches for planets around stars that are not amenable to high-precision radial-velocity observations, and a search for large rocky planets around
nearby low-mass 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.
The LINC-NIRVANA instrument is a 1-2.5 micron Fizeau interferometric imager, which combines the light of the two 8.4 m mirrors of the Large Binocular Telescope on Mt. Graham in Arizona. The cryogenic camera forms the heart of the science channel of this instrument, delivering a 1 arcmin diameter field of view with 5 mas spatial resolution. The center 10x10 arcseconds, initially limited by the size of the 2048x2048 Hawaii-2 detector, are used for science observations. For simplicity, the camera has a fixed, F/32 optical path of the combined beams, leading to wavelength-dependent sampling. We describe the main components of the camera, as well as present the calculations of interferometric performance and the required opto-mechanical tolerances. We demonstrate that specially designed components can reach these specifications.
LUCIFER (LBT NIR Spectrograph Utility with Camera and Integral-Field
Unit for Extragalactic Research) is a NIR spectrograph and imager for
the LBT (Large Binocular Telescope) working in the wavelength range from 0.9 to 2.5 microns. The instrument is to be built by a consortium of five german institutes (Landessternwarte Heidelberg (LSW), Max Planck Institut for Astronomy (MPIA), Max Planck Institut for Extraterrestric Physics (MPE), Astronomical Institut of the Ruhr-University Bochum (AIRUB) and Fachhochschule for Technics and Design Mannheim (FHTG)). LUCIFER will be one of the first light instruments of the LBT and will be available to the community at the end of 2005. A copy of the instrument for the second LBT mirror follows about one year later.
The paper presents a brief status report of the procured and built
hardware, of the workpackages already carried out and summarizes the ongoing work in progress.
The MPIA in Heidelberg has built many instruments for IR observation over the years. While the previous instruments were moderate in size and could easily be enclosed in a liquid nitrogen dewar, future instruments will require different cooling concepts. The use of Gifford McMahon coolers was chosen for some instruments, but has the disadvantage of low frequency vibrations. The recently-developed pulse tube coolers have lower vibrations but other disadvantages. For the LINC-NIRVANA cryostat, we plan to build a cooling system with a constant flow of Helium through a heat exchanger inside the cryostat. This cooling concept could also be expanded to future instrumentation for the next generation of telescopes.
Omega2000 is the first near infrared (NIR) wide field camera installed on the 3.5 m telescope at Calar Alto which operates with a 2kx2k HAWAII-2 FPA. Each component of the camera system must suit high requirements to exploit the facilities provided by the imaging sensor. To meet these requirements was a great challenge in design and realization of the optics, the mechanical part and the electronics. The cryogenic optical system with a warm mirror baffle can produce excellent optical quality and high sensitivity over the whole 15.4x15.4 arcmin field of view. The readout electronics together with the camera control software provide multi functional data acquisition and the camera control software can perform the readout and on-line data reduction simultaneously at a high data rate. Different operational and readout modes of the data acquisition of the detector both for engineering and scientific purpose were implemented, tested and optimized and the characteristics of three HAWAII-2 detectors were also determined
in their hardware and software environment. Initial astronomical
observations were carried out successfully in autumn 2003.
LINC-NIRVANA is a Fizeau interferometer which will be built for the Large Binocular Telescope (LBT). The LBT exists of two 8.4m mirrors on one mounting with a distance of 22.8m between the outer edges of the two mirrors. The interferometric technique used in LINC-NIRVANA provides direct imaging with the resolution of a 23m telescope in one direction and 8.4m in the other. The instrument uses multi-conjugated adaptive optics (MCAO) to increase the sky coverage and achieve the diffraction limit in J, H, K over a moderate Field of View (2 arcmin in diameter). During the preliminary design phase the team faced several problems similar to those for an instrument at a 23m telescope. We will give an overview of the current design, explain problems related to 20m class telescopes and present solutions.
LUCIFER (LBT NIR-Spectroscopic Utility with Camera and Integral-Field Unit for Extragalactic Research) is a NIR spectrograph and imager for the Large Binocular Telescope (LBT) on Mt. Graham, Arizona. It is built by a consortium of five German institutes and will be one of the first light instruments for the LBT. Later, a second copy for the second mirror of the telescope will follow.
Both instruments will be mounted at the bent Gregorian foci of the two individual telescope mirrors. The final design of the instrument is presently in progress.
LUCIFER will work at cryogenic temperature in the wavelength range from 0.9 μm to 2.5 μm. It is equipped with three exchangeable cameras for imaging and spectroscopy: two of them are optimized for seeing-limited conditions, the third camera for the diffraction-limited
case with the LBT adaptive secondary mirror working. The spectral resolution will allow for OH suppression. Up to 33 exchangeable masks will be available for longslit and multi-object spectroscopy (MOS) over the full field of view (FOV). The detector will be a Rockwell HAWAII-2 HgCdTe-array.
Omega2000 is a prime focus near infrared (NIR) wide-field camera for the 3.5 meter telescope at Calar Alto/Spain. Having a large field of view and an excellent optical quality, the instrument is particularly designed for survey observations. A cryogenic four lens focal reducer delivers a 15.4 x 15.4 arcminute field of view (FOV) with a pixel scale of 0.45"/pixel. The lenses are made of various optical materials, including CaF2 and BaF2 with diameters of up to 150 mm. They must be specially mounted to survive cooling and to follow the tight tolerances (± 0.05 mm for lens centricity and ± 30 arcsec for lens tilt) required by the optical design. For a wide range of observing applications, a filter mechanism can hold up to 17 filters of 3 inch diameter in 3 filter wheels. For exact and reproducible filter positions, a mechanical locking mechanism has been developed which also improves the cool-down performance of the filter wheels and filters. This mechanism allows a minimum distance of about 3 mm between the filter wheels. A Rockwell HAWAII-2 FPA is used to cover the wavelength range from 0.85 μm to 2.4 μm. Special care has been taken with regard to the thermal coupling of the detector. The thermal connection is made by gold layers on the fanout board and an additional spring-loaded mechanism. A warm mirror baffle system has been developed, in order to minimize the thermal background for K band observations. The camera is a focal reducer only and has no cold pupil stop.
Detection of faint companions near bright stars requires the usage of high dynamic range instrumentation. The four quadrant phase mask is a quite efficient nulling device for the light of on-axis stars as shown by simulations. We conducted a test of the true performance of this concept starting with the manufacturing of the optical element, continuing with the installation in the telescope and the usage of the Adaptive Optics system. A four quadrant phase mask was installed in the 3.5m telescope on Calar Alto and several tests with both an artificial source and natural stars were conducted. Tests in order to detect faint companions around HD 140913, TRN 1 and HD 161797 were successful for the last target and also, although almost serendipitously, in the case of HD144004. The main limitations found for the phase mask cancelling effect at relatively low Strehl ratios (16%-63%) were the residual tip-tilt of our system and the control of placement of the mask in the optical train.
Fizeau interferometry at the Large Binocular Telescope (LBT) offers significant advantages over other facilities in terms of spatial resolution, field of view, and sensitivity. We provide an update of the LINC-NIRVANA project, which aims to bring a near-infrared and visible wavelength Fizeau beam combiner to the LBT by late 2005. As with any complex instrument, a number of detailed requirements drive the final design adopted.
In order to achieve moderate Field of View (2 arcmin in diameter) and nearly diffraction limited capabilities, at the reddest portion of the visible spectrum in the interferometric mode of LBT, two sophisticated MCAO channels are required. These are being designed to perform a detailed correction of the atmospheric turbulence through three deformable mirrors per telescope arm: the secondary adaptive mirror and two commercial piezostack mirrors, leading to an overall number of degree of freedom totaling ~ 3000. A combination of numerical and optical coaddition of light collected from natural reference stars located inside the scientific Field of View and in an annular region, partially vignetted, and extending up to ≈ 6 arcmin in diameter, allows for such a performance with individual loops characterized by a much smaller number of degree of freedom, making the real-time computation, although still challenging, to more reasonable levels. We implement in the MCAO channel the dual Field of View layer-oriented approach using natural guide stars, only allowing for limited, but significant, sky coverage.
The objective of the PYRAMIR project is to complement the Calar Alto Adaptive Optics System - ALFA - with a new pyramid wavefront sensor working in the near IR, replacing the previous tip-tilt tracker arm. Here we describe the Science as well as the Technical motivation for such a system. The optical design will be presented, discussing the particular requirements posed by sensing the wavefronts in the infrared like a cooling system for the opto-mechanical components, etc. We will also talk about the components, like the IR detector we plan to use - PICNIC, as one option, the sucessor of NICMOS3 from Rockwell, together with the AO-Multiplexer. It is described how we expect to integrate the system into the optical, machanical, electronical and control architecture of ALFA.
The ongoing development of large IR array detectors has enabled wide field, deep surveys to be undertaken. There are, however, a number of challenges in building an IR instrument which has both excellent optical quality and high sensitivity over a wide field. We discuss these problems in the context of building a wide field imaging camera for the 3.5m telescope at Calar Alto with the new 2K by 2K HgCdTe HAWAII-2 focal plane array. Our final design is a prime focus camera with a 15 feet field-of-view, called Omega 2000. To achieve excellent optical quality over the whole field, we have had to dispense with the reimaging optics and cold Lyot stop. We show that creative baffling schemes, including the use of undersized baffles, can compensate for the lost K band sensitivity. A moving baffle will be employed in Ogema 2000 to allow full transmission in the non-thermal J and H bands.
First laboratory test result of CONICA are presented for the variety of observation modes: using the final ALADDIN- Detector, IR images in direct, spectroscopic and polarimetric modes are compared to theoretically expected diffraction limited point spread functions. In long slit spectroscopy, wavelength calibration and spectral resolution is demonstrated for the different grism, slit and camera combinations.
In this paper, we briefly review the status of interferometry on the Large Binocular Telescope (LBT) and introduce LINC, a near-infrared beam combiner we have proposed for the LBT. We present some key science programs, and we conclude with a discussion of how we are approaching LINC's optical design.
Omega Prime is a wide-field near-IR camera for the prime focus of the Calar Alto 3.5 m telescope in Spain. The detector is a 1024 X 1024 pixel HAWAII array made by Rockwell. The image scale is 0.4 arcsec/pixel, giving a field of view of 6.8 by 6.8 arcmin. In order to maximize the throughput, the optics were designed as a prime focus corrector with only three lenses. This simple design without a cold pupil provides an excellent image quality over the entire field of view. To reduce thermal background at wavelengths longer than 2.2 micrometers , Omega Prime has a series of cold internal baffles and an additional torodial mirror outside the dewar. This annular reflector causes detector pixels to 'see' mostly the cold interior of the camera. The camera has been in operation since May 1996 and has been used for a variety of scientific programs. Including a very deep K survey covering 1000 square arcmin to a 5 (sigma) limit for point-sources of 20.5 magnitude.
A high resolution near IR camera (CONICA) for the firs VLT unit is under development, which will provide diffraction limited spatial resolution being combined with the adaptive optics system NAOS. CONICA serves as a multi-mode instrument for the wavelength region between 1.0 and 5.0 micrometers , offering broad band, narrow band or Fabry Perot direct imaging capabilities, polarimetric modes using Wollaston prism or wire grid analyzers and long slit spectroscopy up to a spectral resolution of about 1000 per two pixel. We presented a first concept of CONICA in 1995. In the mean time, large parts of the instrument have been manufactured, the cryostat and the adapter have been finished and first cryogenic test have been performed. This paper describes the actual design and status of development of CONICA focusing on those aspects which have not been described in detail before or the design of which have been changed in the mean time.
Omega Cass is the new MPIA multi-mode camera for imaging and spectroscopy at near IR wavelengths between 1.0 and 2.5 micrometers . The Camera is equipped with an 1024 X 1024 HAWAII HgCdTe focal plane array from Rockwell. The cryogenic re- imaging optics are designed to cover a wide variety of observing conditions. The imaging scales can be changed during observations, allowing the observer to react to changing conditions. Three different lens sets provide scales of 0.3, 0.2 and 0.1 arcsec/pixel at the f/10 Cassegrain focus of the 3.5m telescope. In combination with a laser based adaptive optics system, available at the same telescope, these imaging scale correspond to 0.12, 0.08 and 0.04 arcsec/pixel, which double samples the diffraction limit at the shortest operation wavelength. A set of grisms allow low to medium resolution long slit spectroscopy up to R equals 1000. In addition, sensitive polarimetry can be done with Wollaston prisms and wire grid analyzers. Omega-Cass is mainly designed for the 3.5m telescope on Calar Alto, although it may be used at any other telescopes with a focal ratio slower than f/8, including the MPIA's 2.2m telescopes on Calar Alto and La Silla.
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