Rafael Probst, Gaspare Lo Curto, Gerardo Ávila, Anna Brucalassi, Bruno Canto Martins, Izan de Castro Leão, Massimiliano Esposito, Jonay González Hernández, Frank Grupp, Theodor Hänsch, Ronald Holzwarth, Hanna Kellermann, Florian Kerber, Olaf Mandel, Antonio Manescau , Luca Pasquini, Eszter Pozna, Rafael Rebolo, José Renan de Medeiros, Sebastian Stark, Tilo Steinmetz, Alejandro Suárez Mascareño, Thomas Udem, Josefina Urrutia, Yuanjie Wu
We report on the installation of a laser frequency comb (LFC) at the HARPS spectrograph, which we characterize relative to a second LFC that we had brought to HARPS for testing. This allowed us for the first time to probe the relative stability of two independent astronomical LFCs over an extended wavelength range. Both LFCs covered the spectral range of HARPS at least from 460 to 690 nm. After optimization of the fiber coupling to HARPS to suppress modal noise, a relative stability of the two LFCs in the low cm/s range was obtained. In combination with the results of our four earlier LFC test campaigns on HARPS, the available data now cover a time span of more than six years.
MATISSE is the second-generation mid-infrared spectrograph and imager for the Very Large Telescope Interferometer (VLTI) at Paranal. This new interferometric instrument will allow significant advances by opening new avenues in various fundamental research fields: studying the planet-forming region of disks around young stellar objects, understanding the surface structures and mass loss phenomena affecting evolved stars, and probing the environments of black holes in active galactic nuclei. As a first breakthrough, MATISSE will enlarge the spectral domain of current optical interferometers by offering the L and M bands in addition to the N band. This will open a wide wavelength domain, ranging from 2.8 to 13 μm, exploring angular scales as small as 3 mas (L band) / 10 mas (N band). As a second breakthrough, MATISSE will allow mid-infrared imaging - closure-phase aperture-synthesis imaging - with up to four Unit Telescopes (UT) or Auxiliary Telescopes (AT) of the VLTI. Moreover, MATISSE will offer a spectral resolution range from R ∼ 30 to R ∼ 5000. Here, we present one of the main science objectives, the study of protoplanetary disks, that has driven the instrument design and motivated several VLTI upgrades (GRA4MAT and NAOMI). We introduce the physical concept of MATISSE including a description of the signal on the detectors and an evaluation of the expected performances. We also discuss the current status of the MATISSE instrument, which is entering its testing phase, and the foreseen schedule for the next two years that will lead to the first light at Paranal.
CRIRES at the VLT is one of the few adaptive optics enabled instruments that offer a resolving power of 105 from 1 − 5 μm. An instrument upgrade (CRIRES+) is proposed to implement cross-dispersion capabilities, spectro-polarimetry modes, a new detector mosaic, and a new gas absorption cell. CRIRES+ will boost the simultaneous wavelength coverage of the current instrument (~ γ/70 in a single-order) by a factor of 10 in the cross-dispersed configuration, while still retaining a ~> 10 arcsec slit suitable for long-slit spectroscopy. CRIRES+ dramatically enhances the instrument’s observing efficiency, and opens new scientific opportunities. These include high-precision radial-velocity studies on the 3 m/s level to characterize extra-solar planets and their athmospheres, which demand for specialized, highly accurate wavelength calibration techniques. In this paper, we present a newly developed absorption gas-cell to enable high-precision wavelength calibration for CRIRES+. We also discuss the strategies and developments to cover the full operational spectral range (1 − 5 μµm), employing cathode emission lamps, Fabry-Perot etalons, and absorption gas-cells.
The CRIRES infrared spectrograph at the European Southern Observatory (ESO) Very Large Telescope (VLT)
facility will soon receive an upgrade. This upgrade will include the addition of a module for performing highresolution
spectropolarimetry. The polarimetry module will incorporate a novel infrared beamsplitter based on
polarization gratings (PGs). The beamsplitter produces a pair of infrared output beams, with opposite circular
polarizations, which are then fed into the spectrograph. Visible light passes through the module virtually
unaltered and is then available for use by the CRIRES adaptive optics system. We present the design of the
polarimetry module and measurements of PG behavior in the 1 to 2.7 μm wavelength range.
MATISSE is the mid-infrared spectrograph and imager for the Very Large Telescope Interferometer (VLTI) at Paranal. This second generation interferometry instrument will open new avenues in the exploration of our Universe. Mid-infrared interferometry with MATISSE will allow significant advances in various fundamental research fields: studies of disks around young stellar objects where planets form and evolve, surface structures and mass loss of stars in late evolutionary stages, and the environments of black holes in active galactic nuclei. MATISSE is a unique instrument. As a first breakthrough it will enlarge the spectral domain used by optical interferometry by offering the L & M bands in addition to the N band, opening a wide wavelength domain, ranging from 2.8 to 13 μm on angular scales of 3 mas (L/M band) / 10 mas (N band). As a second breakthrough, it will allow mid-infrared imaging – closure-phase aperture-synthesis imaging – with up to four Unit Telescopes (UT) or Auxiliary Telescopes (AT) of the VLTI. MATISSE will offer various ranges of spectral resolution between R~30 to ~5000. In this article, we present some of the main science objectives that have driven the instrument design. We introduce the physical concept of MATISSE including a description of the signal on the detectors and an evaluation of the expected performance and discuss the project status. The operations concept will be detailed in a more specific future article, illustrating the observing templates operating the instrument, the data reduction and analysis, and the image reconstruction software.
KEYWORDS: Sensors, Process control, Control systems, Cameras, Telescopes, Signal detection, Data acquisition, Computing systems, Interferometers, Interfaces
GRAVITY is the four-beam, near-infrared, AO-assisted, fringe tracking, astrometric and imaging instrument for the Very Large Telescope Interferometer (VLTI). It is requiring the development of one of the most complex instrument software systems ever built for an ESO instrument. Apart from its many interfaces and interdependencies, one of the most challenging aspects is the overall performance and stability of this complex system. The three infrared detectors and the fast reflective memory network (RMN) recorder contribute a total data rate of up to 20 MiB/s accumulating to a maximum of 250 GiB of data per night. The detectors, the two instrument Local Control Units (LCUs) as well as the five LCUs running applications under TAC (Tools for Advanced Control) architecture, are interconnected with fast Ethernet, RMN fibers and dedicated fiber connections as well as signals for the time synchronization. Here we give a simplified overview of all subsystems of GRAVITY and their interfaces and discuss two examples of high-level applications during observations: the acquisition procedure and the gathering and merging of data to the final FITS file.
CRIRES, the ESO high resolution infrared spectrometer, is a unique instrument which allows astronomers to access a
parameter space which up to now was largely uncharted. In its current setup, it consists of a single-order spectrograph
providing long-slit, single-order spectroscopy with resolving power up to R=100,000 over a quite narrow spectral range.
This has resulted in sub-optimal efficiency and use of telescope time for all the scientific programs requiring broad
spectral coverage of compact objects (e.g. chemical abundances of stars and intergalactic medium, search and
characterization of extra-solar planets). To overcome these limitations, a consortium was set-up for upgrading CRIRES
to a cross-dispersed spectrometer, called CRIRES+. This paper presents the updated optical design of the cross-dispersion
module for CRIRES+. This new module can be mounted in place of the current pre-disperser unit. The new
system yields a factor of >10 increase in simultaneous spectral coverage and maintains a quite long slit (10”), ideal for
observations of extended sources and for precise sky-background subtraction.
We present the latest update of the European Southern Observatory's Very Large Telescope interferometer (VLTI). The operations of VLTI have greatly improved in the past years: reduction of the execution time; better offering of telescopes configurations; improvements on AMBER limiting magnitudes; study of polarization effects and control for single mode fibres; fringe tracking real time data, etc. We present some of these improvements and also quantify the operational improvements using a performance metric. We take the opportunity of the first decade of operations to reflect on the VLTI community which is analyzed quantitatively and qualitatively. Finally, we present briefly the preparatory work for the arrival of the second generation instruments GRAVITY and MATISSE.
CRIRES is one of the few IR (0.92-5.2 μm) high-resolution spectrographs in operation at the VLT since 2006. Despite
good performance it suffers a limitation that significantly hampers its ability: a small spectral coverage per exposure. The
CRIRES upgrade (CRIRES+) proposes to transform CRIRES into a cross-dispersed spectrograph while maintaining the
high resolution (100000) and increasing the wavelength coverage by a factor 10 compared to the current capabilities. A
major part of the upgrade is the exchange of the actual cryogenic pre-disperser module by a new cross disperser unit. In
addition to a completely new optical design, a number of important changes are required on key components and
functions like the slit unit and detectors units. We will outline the design of these new units fitting inside a predefined
and restricted space. The mechanical design of the new functions including a description and analysis will be presented.
Finally we will present the strategy for the implementation of the changes.
The quality of data obtained by VLTI instruments may be refined by analyzing the continuous data supplied by the
Reflective Memory Network (RMN). Based on 5 years experience providing VLTI instruments (PACMAN, AMBER,
MIDI) with RMN data, the procedure has been generalized to make the synchronization with observation trouble-free.
The present software interface saves not only months of efforts for each instrument but also provides the benefits of
software frameworks. Recent applications (GRAVITY, MATISSE) supply feedback for the software to evolve. The
paper highlights the way common features been identified to be able to offer reusable code in due course.
High-resolution infrared spectroscopy plays an important role in astrophysics from the search for exoplanets to
cosmology. Yet, many existing infrared spectrographs are limited by a rather small simultaneous wavelength coverage.
The AO assisted CRIRES instrument, installed at the ESO VLT on Paranal, is one of the few IR (0.92-5.2 μm) highresolution
spectrographs in operation since 2006. However it has a limitation that hampers its efficient use: the
wavelength range covered in a single exposure is limited to ~15 nanometers. The CRIRES Upgrade project (CRIRES+)
will transform CRIRES into a cross-dispersed spectrograph and will also add new capabilities. By introducing crossdispersion
elements the simultaneously covered wavelength range will be increased by at least a factor of 10 with respect
to the present configuration, while the operational wavelength range will be preserved. For advanced wavelength
calibration, new custom made absorption gas cells and etalons will be added. A spectro-polarimetric unit will allow one
for the first time to record circularly polarized spectra at the highest spectral resolution. This will be all supported by a
new data reduction software which will allow the community to take full advantage of the new capabilities of CRIRES+.
The Observation Software (OS) is the top level control software of astronomical instruments which is managing the
actions during exposures and calibrations carried out at ESO (at various sites VLT, VLTI, La Silla, VISTA). The
software framework Base Observation Software Stub (BOSS) provides the foundation of the OS, in use for a decade.
BOSS contains 26000 lines of C++ code and covers the functionalities of a simple OS (configuration, synchronization of
the subsystems, state alignment, exposure and image file handling). The need for ever increasing precision and speed
imposes a consequent increase in complexity on the astronomical instrument control software. Thus makes the OS a
critical component in the instrument design. This is reflected by the size of the BOSS applications varying between 0-12000 lines including additional scheduler mechanism, calculation of optical phenomena, online calibrations etc. This
article focuses on the progress of OS and BOSS, and their functionality over time.
The Phase Referenced Imaging and Micro Arcsecond Astrometry (PRIMA) facility for the Very Large Telescope
Interferometer (VLTI), is being installed and tested in the observatory of Paranal. Since January 2011 the
integration and individual testing of the different subsystem has come to a necessary minimum. At the same
time the astrometric commissioning phase has begun.
In this contribution we give an update on the status of the facility and present some highlights and difficulties
on our way from first dual-feed fringe detection to first astrometric measurements. We focus on technical and
operational aspects. In particular, within the context of the latter we are going to present a modified mode of
operation that scans across the fringes. We will show that this mode, originally only intended for calibration
purposes, facilitates the detection of dual-fringes.
MATISSE is a mid-infrared spectro-interferometer combining the beams of up to four Unit Telescopes or Auxiliary
Telescopes of the Very Large Telescope Interferometer (VLTI) of the European Southern Observatory.
MATISSE will constitute an evolution of the two-beam interferometric instrument MIDI. New characteristics present in
MATISSE will give access to the mapping and the distribution of the material, the gas and essentially the dust, in the
circumstellar environments by using the mid-infrared band coverage extended to L, M and N spectral bands. The four
beam combination of MATISSE provides an efficient uv-coverage: 6 visibility points are measured in one set and 4
closure phase relations which can provide aperture synthesis images in the mid-infrared spectral regime.
We give an overview of the instrument including the expected performances and a view of the Science Case. We present
how the instrument would be operated. The project involves the collaborations of several agencies and institutes: the
Observatoire de la Côte d’Azur of Nice and the INSU-CNRS in Paris, the Max Planck Institut für Astronomie of
Heidelberg; the University of Leiden and the NOVA-ASTRON Institute of Dwingeloo, the Max Planck Institut für
Radioastronomie of Bonn, the Institut für Theoretische Physik und Astrophysik of Kiel, the Vienna University and the
Konkoly Observatory.
The Phase Referenced Imaging and Micro Arcsecond Astrometry (PRIMA) facility for the Very Large Telescope
Interferometer (VLTI), is being installed and tested in the observatory of Paranal. Most of the tests have been
concentrated on the characterization of the Fringe Sensor Unit (FSU) and on the automation of the fringe
tracking in preparation of dual-field observations. The status of the facility, an analysis of the FSU performance
and the first attempts towards dual-field observations will be presented in this paper. In the FSU, the phase
information is spatially encoded into four independent combined beams (ABCD) and the group delay comes from
their spectral dispersion over 5 spectral channels covering the K-band. During fringe tracking the state machine
of the optical path difference controller is driven by the Signal to Noise Ratio (SNR) derived from the 4 ABCD
measurements. We will describe the strategy used to define SNR thresholds depending on the star magnitude
for automatically detecting and locking the fringes. Further, the SNR as well as the phase delay measurements
are affected by differential effects occurring between the four beams. We will shortly discuss the contributions
of these effects on the measured phase and SNR noises. We will also assess the sensitivity of the group delay
linearity to various instrumental parameters and discuss the corresponding calibration procedures. Finally we
will describe how these calibrations and detection thresholds are being automated to make PRIMA as much as
possible a user-friendly and efficient facility.
KEYWORDS: Sensors, Calibration, Metrology, Fourier transforms, Phase shifts, Modulation, Signal to noise ratio, Large telescopes, Time metrology, Computer architecture
The dual feed astrometric instrument software of PRIMA (PACMAN) that is currently being integrated at the VLTI will
use two spatially modulated fringe sensor units and a laser metrology system to carry out differential astrometry. Its
software and hardware compromises a distributed system involving many real time computers and workstations
operating in a synchronized manner. Its architecture has been designed to allow the construction of efficient and flexible
calibration and observation procedures. In parallel, a novel scheme of integrating M-code (MATLAB/OCTAVE) with
standard VLT (Very Large Telescope) control software applications had to be devised in order to support numerically
intensive operations and to have the capacity of adapting to fast varying strategies and algorithms. This paper presents
the instrument software, including the current operational sequences for the laboratory calibration and sky calibration.
Finally, a detailed description of the algorithms with their implementation, both under M and C code, are shown together
with a comparative analysis of their performance and maintainability.
The Observation Software (OS) of astronomical instruments, which lie directly beneath the instructions of astronomers,
carrying out exposures and calibrations is the supervisor of the multi-process and multi-layer instrument software
package. The main responsibility of the OS is the synchronization of the subsystems (detectors and groups of mechanical
devices) and the telescope during exposures. At ESO a software framework Base Observation Software Stub (BOSS)
takes care of the common functionalities of all OS of various instruments at the various sites VLT, VLTI, La Silla and
Vista. This paper discusses the latest applications and how their new generic requirements contributes to the BOSS
framework. The paper discusses the resolution of problems of event queues, interdependent functionalities, parallel
commands and asynchronous messages in the OS using OO technologies.
The VLTI control architecture is based on a real time distributed system involving dozens of specialized computers.
Several control loops are required to run the VLTI, e.g. for fringe tracking, angle tracking, injection optimization and
vibration cancellation. These control systems rely on a low latency, deterministic shared memory mechanism. It
communicates in the form of a close ring, which includes all devices involved in those loops. Through this ring, sensor
data, intermediate filtered signals, final actuator set-points and feedbacks flow at rates up to 8 kHz. Data in this ring can
be consumed by any node asynchronously. In many cases, those signals are also the astronomical observable (e.g. the
beam combiner fluxes for astrometry) or are used offline, in order to improve the quality of the scientific data reduction
and to debug the system. With the purpose of relieving the control applications of the simultaneous need to record their
signals, a centralized generic recording device has been designed and implemented at the VLTI. In this paper, we
describe its architecture and show that by over-sampling, streaming and posterior filtering on a separate computer it is
possible to overcome the asynchronous nature of the system. We demonstrate that it is feasible to capture data in real
time, verify time reference consistency and store on disk at rates up to ~50 Mbit/s, fulfilling the current VLTI
requirements.
CRIRES is a cryogenic, pre-dispersed, infrared Echelle spectrograph designed to provide a nominal resolving
power ν/Δν of 105 between 1000 and 5000 nm for a nominal slit width of 0.2". The CRIRES installation at
the Nasmyth focus A of the 8-m VLT UT1 (Antu) marks the completion of the original instrumentation plan
for the VLT. A curvature sensing adaptive optics system feed is used to minimize slit losses and to provide 0.2"
spatial resolution along the slit. A mosaic of four Aladdin InSb-arrays packaged on custom-fabricated ceramic
boards has been developed. It provides for an effective 4096 × 512 pixel focal plane array to maximize the free
spectral range covered in each exposure. Insertion of gas cells is possible in order to measure radial velocities with
high precision. Measurement of circular and linear polarization in Zeeman sensitive lines for magnetic Doppler
imaging is foreseen but not yet fully implemented. A cryogenic Wollaston prism on a kinematic mount is already
incorporated. The retarder devices will be located close to the Unit Telescope focal plane. Here we briefly recall
the major design features of CRIRES and describe the commissioning of the instrument including a report of
extensive testing and a preview of astronomical results.
The Observation Software (OS) is the supervisory software which manages all the exposures and calibrations made by an
ESO/VLT instrument. It forms part of the multi-process and multi-layer ESO/VLT instrument software package,
receiving astronomer instructions either from a template script or directly from the instrument's graphical user interface.
In order to speed up development, ease maintenance and hence decrease the costs of the Observation Software of
different instruments (at various sites VLT, VLTI, La Silla, VISTA), a software framework "Base Observation Software
Stub" (BOSS) is supplied by ESO. This article introduces the objectives of the tool collecting the general features of all
instrument OS, such as configuration and synchronization of the subsystems, state alignment, exposure and image file
handling. The basic structure of the implementation is explained (using design patterns), showing the way the
framework copes with a challenge of being constantly adjusted to new generic requirements imposed by the complexity
of new instruments, performance requirements, increasing image file size and file numbers, and at the same time
remaining backward compatible. The instrument-specific features are illustrated via three of many applications:
FLAMES is an example of a complex instrument using a "super OS" controlling three instruments as subsystems;
AMBER is a VLTI instrument; and VISTA has high performance requirements on image file handling.
HAWK-I is a new wide-field infrared camera under development at ESO. With four Hawaii-2RG detectors, a 7.5 arcminute square field of view and 0.1 arcsecond pixels, it will be an optimum imager for the VLT, and a major enhancement to existing and future infrared capabilities at ESO. HAWK-I will eventually make use of ground-layer AO achieved through a deformable secondary mirror/laser guide star facility planned for the VLT.
The adaptive optics MACAO has been implemented in 6 focii of the VLT observatory, in three different flavors. We present in this paper the results obtained during the commissioning of the last of these units, MACAO-CRIRES. CRIRES is a high-resolution spectrograph, which efficiency will be improved by a factor two at least for point-sources observations with a NGS brighter than R=15. During the commissioning, Strehl exceeding 60% have been observed with fair seeing conditions, and a general description of the performance of this curvature adaptive optics system is done.
High resolution spectroscopy made an important step ahead 10 years ago, leading for example to the discovery of numerous exoplanets. But the IR did not benefit from this improvement until very recently. CRIRES will provide a dramatic improvement in the 1-5 micron region in this field. Adaptive optics will allow us increasing both flux and angular resolution on its spectra. This paper describes the adaptive optics of CRIRES, its main limitations, its main components, the principle of its calibration with an overview of the methods used and the very first results obtained since it is installed in the laboratory.
HAWK-I (High Acuity, Wide field K-band Imaging) is a 0.9 μm - 2.5 μm wide field near infrared imager designed to sample the best images delivered over a large field of 7.5 arcmin x 7.5 arcmin. HAWK-I is a cryogenic instrument to be installed on one of the Very Large Telescope Nasmyth foci. It employs a catadioptric design and the focal plane is equipped with a mosaic of four HAWAII 2 RG arrays. Two filter wheels allow to insert broad band and narrow band filters. The instrument is designed to remain compatible with an adaptive secondary system under study for the VLT.
CRIRES is a cryogenic, pre-dispersed, infrared echelle spectrograph designed to provide a resolving power lambda/(Delta lambda) of 105 between 1 and 5mu m at the Nasmyth focus B of the 8m VLT unit telescope #1 (Antu). A curvature sensing adaptive optics system feed is used to minimize slit losses and to provide diffraction limited spatial resolution along the slit. A mosaic of 4 Aladdin~III InSb-arrays packaged on custom-fabricated ceramics boards has been developed. This provides for an effective 4096x512 pixel focal plane array, to maximize the free spectral range covered in each exposure. Insertion of gas cells to measure high precision radial velocities is foreseen. For measurement of circular polarization a Fresnel rhomb in combination with a Wollaston prism for magnetic Doppler imaging is foreseen. The implementation of full spectropolarimetry is under study. This is one result of a scientific workshop held at ESO in late 2003 to refine the science-case of CRIRES. Installation at the VLT is scheduled during the first half of 2005. Here we briefly recall the major design features of CRIRES and describe its current development status including a report of laboratory testing.
KEYWORDS: Control systems, Spectrographs, Telescopes, Computer architecture, Calibration, Observatories, Sensors, Camera shutters, Process control, Software development
FLAMES is a complex observational facility for multi-object spectrography installed at ESO VLT UT2 telescope at Paranal. It consists of a Fibre Positioner that feeds GIRAFFE, a medium-high resolution spectrograph, and UVES, a high resolution stand-alone spectrograph operational in slit mode since 1999. The Positioner is the core component of FLAMES. It is a rather large and complex system comprising two spherical focal plates of approx. 90 cm in diameter, an exchanger mechanism, R-θ robot motions and a pneumatic gripper mechanism with a built in miniature CCD camera. The main task of the Positioner is to place a fibre (button) at a given focal plate position with accuracy better than 40 microns. The fibre positioning process is performed on the plate attached to the robot while an observation is being performed on the plate attached to the telescope rotator. The whole instrument is driven by software designed in accordance with the VLT Common Software standards, allowing the complete integration of the instrument in the VLT environment. The paper mainly focuses on two areas: the low level control and the performance of the Fibre Positioner; and the high level coordinating software architecture that provides facility for parallel operations of multiple instruments.
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