The construction of a diffraction limitable telescope as large as the ESO’s ELT is enabled by its embedded deformable quaternary mirror. Besides its essential function in the telescope control, M4 also contributes to compensating the free atmosphere aberrations for all post-focal AO applications. The paper presents how the telescope manages M4 to maintain its optical performance while offering to the instruments a clean wavefront interface, supporting the desired AO functionalities. The paper reviews the telescope strategy to derive its wavefront dynamic properties directly from the analysis of the control data collected in science mode, with the goal to minimize the observatory time spent on dedicated wavefront calibration tasks.
We present an optomechanical test bench setup (MELT) for testing and validating key functionalities to be used on the Extremely Large Telescope (ELT) during the periods of system verification, wavefront control commissioning, through the handover to science, up to regular diagnostic, monitoring, and validation tasks during operations. <p> </p>The main objectives of MELT are to deploy and validate the telescope control system, to deploy and validate wavefront control algorithms for commissioning and operations, as well as to produce and validate key requirements for the phasing and diagnostic station (PDS) of the ELT.<p> </p> The purpose of MELT is to deploy optomechanical key components such as a segmented primary mirror, a secondary mirror on a hexapod, an adaptive fourth mirror, and a fast tip/tilt mirror together with their control interfaces that emulate the real telescope optomechanical conditions. The telescope control system, deployed on MELT can test control schemes with the active mounts emulating the real ELT optomechanical control interfaces. <p> </p>The presented optomechanical setup uses the Active Segmented Mirror (ASM) with its piezo-driven 61 segments and a diameter of 15 cm. It was designed, built, and used on sky during the Active Phasing Experiment (APE). <p> </p>Several beam paths after the telescope optical train on MELT are conditioned and guided to wavefront sensors and cameras, sensitive to wavelength bands in the visible and infrared to emulate wavefront commissioning and phasing tasks. This optical path resembles part of the phasing and diagnostics station (PDS) of the ELT, which is used to acquire the first star photons through the ELT and to learn the usage and control of all the ELT optomechanics. The PDS will be developed, designed, and built in-house at ESO. MELT helps its design by providing a detailed test setup for defining and deploying system engineering tasks, such as detailed functional analysis, definition of tasks to be carried out, and technical requirements, as well as operational commissioning aspects. <p> </p>The bench test facility MELT will in the end help us to be as much as possible prepared when the telescope sends the first star light through the optical train to be able to tackle the unforeseeable problems and not be caught up with the foreseeable ones.
Fighting vibrations on large telescopes is an arduous task. At Gemini, vibrations originating from cryogenic coolers have been shown to degrade the optical wavefront, in certain cases by as much as 40%. This paper discusses a general solution to vibration compensation by tracking the real time vibration state of the telescope and using M2 to apply corrections. Two approaches are then presented: an open loop compensation at M2 based on the signal of accelerometers at the M1 glass, and a closed loop compensation at M2 based on optical measurements from the wave front sensor. The paper elaborates on the pros and cons of each approach and the challenges faced during commissioning. A conclusion is presented with the final results of vibration tracking integrated with operations.
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.
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.
We report the results of a multi-year program to measure the vibration characteristics of the two Gemini telescopes. Measurements with fast-guiding wavefront sensors and networks of accelerometers show a correlation between image motion and optical vibrations induced mostly by instrument cryocoolers. We have mitigated the strongest vibrations by fast-guiding compensation and active cancellation of vibration sources.
We study the impact of various telescope effects (like effect of phasing errors, missing segments, etc) on the performance of SCAO systems. This paper is using the E-ELT with 798 primary mirror segments. For example, we will show what kind of AO system (number of sub-apertures, frame-rate) is necessary to compensate for these effects, to get a fully seeing limited performance from the telescope.
GRAVITY is a near-infrared interferometric instrument that allows astronomers to combine the light of the four unit or four auxiliary telescopes of the ESO Very Large Telescope in Paranal, Chile. GRAVITY will deliver extremely precise relative astrometry and spatially resolved spectra. In order to study objects in regions of high extinction (e.g. the Galactic Center, or star forming regions), GRAVITY will use infrared wavefront sensors. The suite of four wavefront sensors located in the Coudé room of each of the unit telescopes are known as the Coudé Integrated Adaptive Optics (CIAO). The CIAO wavefront sensors are being constructed by the Max Planck Institute for Astronomy (MPIA) and are being installed and commissioned at Paranal between February and September of 2016. This presentation will focus on system tests performed in the MPIA adaptive optics laboratory in Heidelberg, Germany in preparation for shipment to Paranal, as well as on-sky data from the commissioning of the first instrument. We will discuss the CIAO instruments, control strategy, optimizations, and performance at the telescope.
GRAVITY is a second generation near-infrared VLTI instrument that will combine the light of the four unit or four auxiliary telescopes of the ESO Paranal observatory in Chile. The major science goals are the observation of objects in close orbit around, or spiraling into the black hole in the Galactic center with unrivaled sensitivity and angular resolution as well as studies of young stellar objects and evolved stars. In order to cancel out the effect of atmospheric turbulence and to be able to see beyond dusty layers, it needs infrared wave-front sensors when operating with the unit telescopes. Therefore GRAVITY consists of the Beam Combiner Instrument (BCI) located in the VLTI laboratory and a wave-front sensor in each unit telescope Coudé room, thus aptly named Coudé Infrared Adaptive Optics (CIAO). This paper describes the CIAO design, assembly, integration and verification at the Paranal observatory.
In this paper, we present an algorithm and supporting simulations results showing how a single conjugated AO system
can be used to detect a scalloping error occurring in the telescope. We show that when the scalloping error modes are
entered in the reconstruction modal basis, the Deformable Mirror shape can be used to estimate the scalloping error
through a simple matrix vector multiply. Temporal averaging allows to get rid of the atmospheric noise on the scalloping
measurement assuming a perfect “scalloping actuator” and to get a measurement accuracy of about 20nm rms.
In the summer of 2011, the first on-sky astrometric commissioning of PRIMA-Astrometry delivered a performance of 3 m″ for a 10 ″ separation on bright objects, orders of magnitude away from its exoplanet requirement of 50 μ″ ~ 20 μ″ on objects as faint as 11 mag ~ 13 mag in K band. This contribution focuses on upgrades and characterizations carried out since then. The astrometric metrology was extended from the Coudé focus of the Auxillary Telescopes to their secondary mirror, in order to reduce the baseline instabilities and improve the astrometric performance. While carrying out this extension, it was realized that the polarization retardance of the star separator derotator had a major impact on both the astrometric metrology and the fringe sensors. A local compensation of this retardance and the operation on a symmetric baseline allowed a new astrometric commissioning. In October 2013, an improved astrometric performance of 160 μ″ was demonstrated, still short of the requirements. Instabilities in the astrometric baseline still appear to be the dominating factor. In preparation to a review held in January 2014, a plan was developed to further improve the astrometric and faint target performance of PRIMA Astrometry. On the astrometric aspect, it involved the extension of the internal longitudinal metrology to primary space, the design and implementation of an external baseline metrology, and the development of an astrometric internal fringes mode. On the faint target aspect, investigations of the performance of the fringe sensor units and the development of an AO system (NAOMI) were in the plan. Following this review, ESO decided to take a proposal to the April 2014 STC that PRIMA be cancelled, and that ESO resources be concentrated on ensuring that Gravity and Matisse are a success. This proposal was recommended by the STC in May 2014, and endorsed by ESO.
GRAVITY is a new generation beam combination instrument for the VLTI. Its goal is to achieve microarsecond astrometric accuracy between objects separated by a few arcsec. This 10<sup>6</sup> accuracy on astrometric measurements is the most important challenge of the instrument, and careful error budget have been paramount during the technical design of the instrument. In this poster, we will focus on baselines induced errors, which is part of a larger error budget.
The E-ELT is an active and adaptive 39-m telescope, with an anastigmat optical solution (5 mirrors including two flats), currently being developed by the European Southern Observatory (ESO). The convex 4-metre-class secondary mirror (M2) is a thin Zerodur meniscus passively supported by an 18 point axial whiffletree. A warping harness system allows to correct low order deformations of the M2 Mirror. Laterally the mirror is supported on 12 points along the periphery by pneumatic jacks. Due to its high optical sensitivity and the telescope gravity deflections, the M2 unit needs to allow repositioning the mirror during observation. Considering its exposed position 30m above the primary, the M2 unit has to provide good wind rejection. The M2 concept is described and major performance characteristics are presented.
For highly segmented primary mirrors, as that of the European Extremely Large Telescope (E-ELT) with its 798 segments, the capability to update regularly the optical phasing solution is essential for robust operations. The duration of standard phasing procedures is driven by the difficulty of maintaining the registration of the image of the primary on the phasing sensor with tolerances of ~0.02% of the mirror diameter. The paper describes a re-phasing procedure with a dynamic range of about ±1.5 microns. This is based on a standard Shack-Hartmann phasing sensor operated at 2 narrow bands filters with wavelength separation of 30%. Controlled registration offsets are applied during the acquisitions, allowing the registration parameters to be estimated from the phasing data. The procedure has been successfully validated at the Gran Telescopio de Canarias (GTC).
In order to evaluate the telescope performance and to derive error budget and stroke allocations a ray-tracing and performance analysis toolkit was developed at the European Southern Observatory (ESO) during project Phase B. Performance estimates and individual error and stroke budget allocations are derived by analyzing the impact of a defined set of perturbations at sub - system level after propagation through a model of the wavefront control. The ray-tracing and performance analysis toolkit is used in parallel to other modeling activities such as structural, control and detailed adaptive optics modeling and provides interfaces to any of those.
The ray-tracing and performance analysis toolkit consists of a set of models each suitable for analyzing sub-systems at a specific temporal and spatial frequency. The impact of quasi - static and dynamic loads is computed by implementing finite element model (FEM) and control model analysis results in optical models which either use linear optical sensitivities or ray - tracing at different levels of resolution.
To predict the performance of the E-ELT three sets of toolkits are developed at ESO: i) The main structure and associated optical unit dynamical and feedback control toolkit, ii) Active optics and phasing toolkit, and iii) adaptive optics simulation toolkit. There was a deliberate policy not to integrate all of the systems into a massive model and tool. The dynamical and control time scale differences are used to separate the simulation environments and tools. Therefore, each toolkit contains an appropriate detail of the problem and holds sufficient overlap with the others to ensure the consistency of the results. In this paper, these toolkits together with some examples are presented.
The image motion (tip/tilt) of the telescope is dominated by two types of perturbations: a) atmospheric b)
wind load. The wind load effect on E-ELT can be an order of magnitude higher than the atmospheric effect.
Part of the image motion due to the wind load on the telescope structure is corrected by the main axis control
system (mainly large amplitude, low frequency errors). The residual tip/tilt is reduced by M5 and M4 mirror
units. M5 with its large stroke and relative low bandwidth (higher than main axes) corrects for large amplitude
and low frequency part of the image motion and M4 unit takes the higher frequency parts with smaller stroke
availability. In this paper the two stage control strategy of the E-ELT field stabilization is introduced. The
performance of the telescope due to the wind load and in the presence of the major imperfections in the control
system is presented.
Control of primary segmented mirror of an extremely large telescope with large number of actuators and sensors
and multiple control loops is a complex problem. The designer of the M1 unit is confronted to the dilemma of
trade-off between the relatively though performance requirements and the robust stability of the control loops.
Another difficulty arises from the contradictory requirements of the stiffness of the segment support system and
position actuators for wind rejection on one hand and vibration mitigation on other hand. The presence of low
frequency mechanical modes of the back structure and possible interaction of the large number of control loops
through such structure could be a limiting factor for achieving the required control bandwidths. To address these
issues a better understanding of dynamical behavior of segmented mirror is necessary. This paper addresses the
trade-offs on dynamical aspects of the M1 segmented mirror and the robust stability conditions of various control
The ESO Very Large Telescope Interferometer (VLTI) offers access to the four 8 m Unit Telescopes (UT) and the four
1.8 m Auxiliary Telescopes (AT) of the Paranal Observatory located in the Atacama Desert in northern Chile. The fourth
AT has been delivered to operation in December 2006, increasing the flexibility and simultaneous baselines access of the
VLTI. Regular science operations are now carried on with the two VLTI instruments, AMBER and MIDI. The FINITO
fringe tracker is now used for both visitor and service observations with ATs and will be offered on UTs in October
2008, bringing thus the fringe tracking facility to VLTI instruments. In parallel to science observations, technical periods
are also dedicated to the characterization of the VLTI environment, upgrades of the existing systems, and development
of new facilities. We will describe the current status of the VLTI and prospects on future evolution.
FINITO (the VLTI three beam fringe-tracker) has been offered in September 2007 to the astronomical community
for observations with the scientific instruments AMBER and MIDI. In this paper, we describe the last
improvements of the fringe-tracking loop and its actual performance when operating with the 1.8m Auxiliary
Telescopes. We demonstrate the gain provided to the scientific observations. Finally, we discuss how FINITO
real-time data could be used in post-processing to enhance the scientific return of the facility.
During the past year the control of the 42m segmented primary mirror of the E-ELT has been studied.
This paper presents the progress in the areas of M1 figure control and control hardware implementation. The critical
issue of coupling through the supporting structure has been considered in the controller design. Different control
strategies have been investigated and from a tradeoff analysis modal control is proposed as a solution addressing the
topics of wind rejection as well as sensor noise in the presence of cross-coupling through the supporting structure.
Various implementations of the M1 Control System have been studied and a centralized architecture has been selected as
baseline. This approach offers maximum flexibility for further iterations. The controller design and main parts of the
control system are described.
The ESO Very Large Telescope Interferometer (VLTI) is the first general-user interferometer that offers near- and mid-infrared long-baseline interferometric observations in service and visitor mode to the whole astronomical community. Over the last two years, the VLTI has moved into its regular science operation mode with the two science instruments, MIDI and AMBER, both on all four 8m Unit Telescopes and the first three 1.8m Auxiliary Telescopes. We are currently devoting up to half of the available time for science, the rest is used for characterization and improvement of the existing system, plus additional installations. Since the first fringes with the VLTI on a star were obtained on March 17, 2001, there have been five years of scientific observations, with the different instruments, different telescopes and baselines. These observations have led so far to more than 40 refereed publications. We describe the current status of the VLTI and give an outlook for its near future.
SINFONI is an Adaptive Optics assisted near infrared Integral Field Spectrometer, currently in the process of installation and commissioning at the Cassegrain focus of VLT Unit Telescope 4 (YEPUN) in Paranal (Chile). The focal plane instrument (SPIFFI) provides simultaneous spectra of 2048 contiguous spatial pixels covering a two dimensional field of view with almost 100% spatial fill factor and with a spectral resolution of ~3500 in the J, H and K bands. It is fed by the Adaptive Optics Module, a 60 elements bimorph deformable mirror technology / curvature sensing system, derived from MACAO and upgraded to Laser Guide Star operations. This papers reports on the Adaptive Optics Module first light (May 31st 2004). Performances in Natural Guide Star mode were validated during the first commissioning and tests were carried out in preparation to the Laser Guide Star mode. Combined operations of the AO-Module with SPIFFI will start during the second commissioning in July. SINFONI is scheduled to be offered to the community in Natural Guide Star mode in April 2005. The commissioning of the instrument in Laser Guide Star mode will take place in the course of 2005 after successful completion of the Laser Guide Star Facility commissioning.
SPIFFI (SPectrometer for Infrared Faint Field Imaging) is a fully cryogenic, near-infrared imaging spectrograph built at the Max-Planck-Institute for Extraterrestrial Physics (MPE) and upgraded with a new detector and spectrograph camera by ASTRON/NOVA, ESO and MPE. The upgraded instrument will become a facility instrument for the ESO VLT in summer 2004 as part of the SINFONI (SINgle Faint Object Near-IR Investigation) project, which is the combination of SPIFFI and ESOs adaptive optics module MACAO (Multiple Application Curvature Adaptive Optics), at the Cassegrain focus of Yepun (UT4). In spring 2003 we had the opportunity to observe with SPIFFI as a guest instrument without the AO-module at the Cassegrain focus of UT2 of the VLT. In this paper we discuss the performance of SPIFFI during the guest-instrument phase. First we summarize the technical performance of SPIFFI like the spatial and spectral resolution, the detector performance and the instruments throughput. Afterwards we illustrate the power of integral field spectroscopy by presenting data and results of the Galactic Center.
The accurate calibration of an AO system is fundamental in order to reach the top performance expected from design. To improve this aspect, we propose procedures for calibrating a curvature AO system in view of optimizing performances and robustness, based on the experience accumulated by the ESO AO team through the development of MACAO systems for VLTI and SINFONI. The approach maximizes the quality of the Interaction Matrix (IM) while maintaining the system in its linear regime and minimizing noise and bias on the measurement.
SINFONI is an adaptive optics assisted near-infrared integral field spectrometer for the ESO VLT. The Adaptive OPtics Module (built by the ESO Adaptive Optics Group) is a 60-elements curvature-sensor based system, designed for operations with natural or sodium laser guide stars. The near-infrared integral field spectrometer SPIFFI (built by the Infrared Group of MPE) provides simultaneous spectroscopy of 32 x 32 spatial pixels, and a spectral resolving power of up to 3300. The adaptive optics module is in the phase of integration; the spectrometer is presented tested in the laboratory. We provide an overview of the project, with particular emphasis on the problems encountered in designing and building an adaptive optics assisted spectrometer.
The European Southern Observatory (ESO) and the Max Planck Institut fur extraterrestrische Physik (MPE) are jointly developing SINFONI, an Adaptive Optics (AO) assisted Near Infrared Integral Field Spectrometer, which will be installed in the first quarter of 2004 at the Cassegrain focus of YEPUN (VLT UT4). The Adaptive Optics Module, a clone of MACAO, designed and built by ESO, is based on a 60 elements curvature system. It feeds the 3D spectrograph, SPIFFI, designed and built by MPE, with higher than 50% K band Strehl for bright (V<12) on-axis Natural Guide Stars (NGS) and less than 35 mas/hour image motion. The AO-Module will be the first curvature AO system operated in Laser Guide Star (LGS) mode, using a STRAP system for the tip/tilt sensing. The Strehl performance in the LGS mode is expected to be better than 30% in K band.
Over the past two years ESO has reinforced its efforts in the field of Adaptive Optics. The AO team has currently the challenging objectives to provide 8 Adaptive Optics systems for the VLT in the coming years and has now a world-leading role in that field. This paper will review all AO projects and plans. We will present an overview of the Nasmyth Adaptive Optics System (NAOS) with its infrared imager CONICA installed successfully at the VLT last year. Sodium Laser Guide Star plans will be introduced. The status of the 4 curvature AO systems (MACAO) developed for the VLT interferometer will be discussed. The status of the SINFONI AO module developed to feed the infrared integral field spectrograph (SPIFFI) will be presented. A short description of the Multi-conjugate Adaptive optics Demonstrator MAD and its instrumentation will be introduced. Finally, we will present the plans for the VLT second-generation AO systems and the researches performed in the frame of OWL.
MACAO stands for Multi Application Curvature Adaptive Optics. A similar concept is applied to fulfill the need for wavefront correction for several VLT instruments. MACAO-VLTI is one of these built in 4 copies in order to equip the Coude focii of the ESO VLT's. The optical beams will then be corrected before interferometric recombination in the VLTI (Very Large Telescope Interferometer) laboratory. MACAO-VLTI uses a 60 elements bimorph mirror and curvature wavefront sensor. A custom made board processes the signals provided by the wavefront detectors, 60 Avalanche Photo-diodes, and transfer them to a commercial Power PC CPU board for Real Time Calculation. Mirrors Commands are sent to a High Voltage amplifier unit through an optical fiber link. The tip-tilt correction is done by a dedicated Tip-tilt mount holding the deformable mirror. The whole wavefront is located at the Coude focus. Software is developed in house and is ESO compatible. Expected performance is a Strehl ratio sligthly under 60% at 2.2 micron for bright reference sources (star V<10) and a limiting magnitude of 17.5 (Strehl ~0.1). The four systems will be installed in Paranal successively, the first one being planned for June 2003 and the last one for June 2004.