Vortex coronagraphs have been shown to be a promising avenue for high-contrast imaging in the close-in environment of stars at thermal infrared (IR) wavelengths. They are included in the baseline design of the mid-infrared extremely large telescope imager and spectrograph. To ensure good performance of these coronagraphs, a precise control of the centering of the star image in real time is needed. We previously developed and validated the quadrant analysis of coronagraphic images for tip-tilt sensing estimator (QACITS) pointing estimator to address this issue. While this approach is not wavelength-dependent in theory, it was never implemented for mid-IR observations, which leads to specific challenges and limitations. Here, we present the design of the mid-IR vortex coronagraph for the “new Earths in the α Cen Region (NEAR) experiment with the Very Large Telescope (VLT)/Very Large Telescope imager and spectrometer for the mid-infrared (VISIR) instrument and assess the performance of the QACITS estimator for the centering control of the star image onto the vortex coronagraph. We use simulated data and on-sky data obtained with VLT/VISIR, which was recently upgraded for observations assisted by adaptive optics in the context of the NEAR experiment. We demonstrate that the QACITS-based correction loop is able to control the centering of the star image onto the NEAR vortex coronagraph with a stability down to 0.015 λ / D rms over 4 h in good conditions. These results show that QACITS is a robust approach for precisely controlling in real time the centering of vortex coronagraphs for mid-IR observations.
The ESO Extremely Large Telescope (ELT) has been in construction since 2014. In parallel with the construction of the telescope, ESO has entered into agreements with consortia in the ESO member states to build the first instruments for that telescope. To meet the telescope science goals, the ambitious instrument plan includes two instruments for first light: an optical to near-infrared integral field spectrograph with a dedicated adaptive optics system (HARMONI) and a near-infrared camera with simple spectrograph (MICADO) behind a multi-conjugate adaptive optics module (MAORY). The next instrument will be a mid-infrared imager and spectrograph (METIS). Plans to follow this first suite of instruments include a high-resolution spectrograph (HIRES) and a multi-object spectrograph (MOSAIC). Technology development is underway to prepare for building the ELT Planetary Camera and Spectrograph. An overview of the telescope and its instruments is given.
The Mid-Infrared ELT Imager and Spectrograph (METIS) is one of three first light instruments on the ELT. It will provide high-contrast imaging and medium resolution, slit-spectroscopy from 3 – 19um, as well as high resolution (R ~ 100,000) integral field spectroscopy from 2.9-5.3µm. All modes observe at the diffraction limit of the ELT, by means of adaptive optics, yielding angular resolutions of a few tens of milliarcseconds. The range of METIS science is broad, from Solar System objects to active galactic nuclei (AGN). We will present an update on the main science drivers for METIS: circum-stellar disks and exoplanets. The METIS project is now in full steam, approaching its preliminary design review (PDR) in 2018. In this paper we will present the current status of its optical, mechanical and thermal design as well as operational aspects. We will also discuss the challenges of building an instrument for the ELT, and the required technologies.
By adding a dedicated coronagraph, ESO in collaboration with the Breakthrough Initiatives, modifies the Very Large Telescope mid-IR imager (VISIR) to further boost the high dynamic range imaging capability this instru- ment has. After the VISIR upgrade in 2012, where coronagraphic masks were first added to VISIR, it became evident that coronagraphy at a ground-based 8m-class telescope critically needs adaptive optics, even at wavelengths as long as 10μm. For VISIR, a work-horse observatory facility instrument in normal operations, this is ”easiest” achieved by bringing VISIR as a visiting instrument to the ESO-VLT-UT4 having an adaptive M2. This “visit” enables a meaningful search for Earth-like planets in the habitable zone around both α-Cen1,2. Meaningful here means, achieving a contrast of ≈ 10-6 within ≈ 0.8arcsec from the star while maintaining basically the normal sensitivity of VISIR. This should allow to detect a planet twice the diameter of Earth. Key components will be a diffractive coronagraphic mask, the annular groove phase mask (AGPM), optimized for the most sensitive spectral band-pass in the N-band, complemented by a sophisticated apodizer at the level of the Lyot stop. For VISIR noise filtering based on fast chopping is required. A novel internal chopper system will be integrated into the cryostat. This chopper is based on the standard technique from early radio astronomy, conceived by the microwave pioneer Robert Dicke in 1946, which was instrumental for the discovery of the 3K radio background.
In this paper we will report on the status of the instrumentation project for the European Southern Observatory's Extremely Large Telescope (ELT). Three instruments are in the construction phase: HARMONI, MICADO and METIS. The multi-conjugate adaptive optics system for MICADO, MAORY, is also under development. Preliminary Design Reviews of all of these systems are planned to be completed by mid-2019. The construction of a laser tomographic module for HARMONI is part of "Phase 2" of the ELT: the design has been advanced to Preliminary Design level in order to define the interface to the HARMONI spectrograph. Preparations for the next instruments have also been proceeding in parallel with the development of these instruments. Conceptual design studies for the multi-object spectrograph MOSAIC, and for the high resolution spectrograph HIRES have been completed and reviewed. We present the current design of each of these instruments and will summarise the work ongoing at ESO related to their development.
A suite of seven instruments and associated AO systems have been planned as the "E-ELT Instrumentation Roadmap". Following the E-ELT project approval in December 2014, rapid progress has been made in organising and signing the agreements for construction with European universities and institutes. Three instruments (HARMONI, MICADO and METIS) and one MCAO module (MAORY) have now been approved for construction. In addition, Phase-A studies have begun for the next two instruments - a multi-object spectrograph and high-resolution spectrograph. Technology development is also ongoing in preparation for the final instrument in the roadmap, the planetary camera and spectrograph. We present a summary of the status and capabilities of this first set of instruments for the E-ELT.
We present an overview of the VISIR instrument after its upgrade and return to science operations. VISIR is the midinfrared imager and spectrograph at ESO’s VLT. The project team is comprised of ESO staff and members of the original VISIR consortium: CEA Saclay and ASTRON. The project plan was based on input from the ESO user community with the goal of enhancing the scientific performance and efficiency of VISIR by a combination of measures: installation of improved hardware, optimization of instrument operations and software support. The cornerstone of the upgrade is the 1k by 1k Si:As AQUARIUS detector array manufactured by Raytheon. In addition, a new prism spectroscopic mode covers the whole N-band in a single observation. Finally, new scientific capabilities for high resolution and high-contrast imaging are offered by sub-aperture mask and coronagraphic modes. In order to make optimal use of favourable atmospheric conditions, a water vapour monitor has been deployed on Paranal, allowing for real-time decisions and the introduction of a user-defined constraint on water vapour. During the commissioning in 2012, it was found that the on-sky sensitivity of the AQUARIUS detector was significantly below expectations. Extensive testing of the detector arrays in the laboratory and on-sky enabled us to diagnose the cause for the shortcoming of the detector as excess low frequency noise. It is inherent to the design chosen for this detector and cannot be remedied by changing the detector set-up. Since this is a form of correlated noise, its impact can be limited by modulating the scene recorded by the detector. After careful analysis, we have implemented fast (up to 4 Hz) chopping with field stabilization using the secondary mirror of the VLT. During commissioning, the upgraded VISIR has been confirmed to be more sensitive than the old instrument, and in particular for low-resolution spectroscopy in the N-band, a gain of a factor 6 is realized in observing efficiency. After overcoming several additional technical problems, VISIR is back in Science Operations since April 2015. In addition an upgrade of the IT infrastructure related to VISIR has been conducted in order to support burst-mode operations. Science Verification of the new modes was performed in Feb 2016. The upgraded VISIR is a powerful instrument providing close to background limited performance for diffraction-limited observations at an 8-m telescope. It offers synergies with facilities such as ALMA, JWST, VLTI and SOFIA, while a wealth of targets is available from survey works like WISE. In addition, it will bring confirmation of the technical readiness and scientific value of several aspects for future mid-IR instrumentation at Extremely Large Telescopes. We also present several lessons learned during the project.
The High Acuity Wide field K-band Imager (HAWK-I) instrument is a cryogenic wide field imager operating in the wavelength range 0.9 to 2.5 microns. It has been in operations since 2007 on the UT4 at the Very Large Telescope Observatory in seeing-limited mode. In 2017-2018, GRound Layer Adaptive optics Assisted by Lasers module (GRAAL) will be in operation and the system GRAAL+HAWK-I will be commissioned. It will allow: deeper exposures for nearly point-source objects, or shorter exposure times for reaching the same magnitude, and/or deeper detection limiting magnitude. With GRAAL, HAWK-I will operate more than 80% of the time with an equivalent K-band seeing of 0.55" (instead of 0.7" without GRAAL). GRAAL is already installed and the operations without adaptive optics were commissioned in 2015. We discuss here the latest updates on performance from HAWK-I without Adaptive Optics (AO) and the preparation for the commissioning of the system GRAAL+HAWK-I.
GRAAL is the adaptive optics module feeding the wide-field IR imager HAWK-I at the VLT observatory. As part of the adaptive optics facility, GRAAL is equipped with 4 Laser-guide star wave-front sensors and provides a large field-of-view, ground layer correction system to HAWK-I. After a successful testing in Europe, the module has been re-assembled in Chile and installed at the Nasmyth-A platform of Yepun, the fourth Unit telescope of the observatory. We report on the installation of GRAAL on the mountain and on its first testing in stand-alone and on-sky.
We present an overview of the VISIR upgrade project. VISIR is the mid-infrared imager and spectrograph at ESO’s
VLT. The project team is comprised of ESO staff and members of the original VISIR consortium: CEA Saclay and
ASTRON. The project plan is based on input from the ESO user community with the goal of enhancing the scientific
performance and efficiency of VISIR by a combination of measures: installation of improved hardware, optimization of
instrument operations and software support. The cornerstone of the upgrade is the 1k by 1k Si:As AQUARIUS detector
array (Raytheon) which has been carefully characterized in ESO’s IR detector test facility (modified TIMMI 2
instrument). A prism spectroscopic mode will cover the N-band in a single observation. New scientific capabilities for
high resolution and high-contrast imaging will be offered by sub-aperture mask (SAM) and phase-mask coronagraphic
(4QPM/AGPM) modes. In order to make optimal use of favourable atmospheric conditions a water vapour monitor has
been deployed on Paranal, allowing for real-time decisions and the introduction of a user-defined constraint on water
vapour. During the commissioning in 2012 it was found that the on-sky sensitivity of the AQUARIUS detector was
significantly below expectations and that VISIR was not ready to go back to science operations. Extensive testing of the
detector arrays in the laboratory and on-sky enabled us to diagnose the cause for the shortcoming of the detector as
excess low frequency noise (ELFN). It is inherent to the design chosen for this detector and can’t be remedied by
changing the detector set-up. Since this is a form of correlated noise its impact can be limited by modulating the scene
recorded by the detector. We have studied several mitigation options and found that faster chopping using the secondary
mirror (M2) of the VLT offers the most promising way forward. Faster M2 chopping has been tested and is scheduled
for implementation before the end of 2014 after which we plan to re-commission VISIR. In addition an upgrade of the IT
infrastructure related to VISIR is planned in order to support burst-mode operations. The upgraded VISIR will be a
powerful instrument providing close to background limited performance for diffraction-limited observations at an 8-m
telescope. It will offer synergy with facilities such as ALMA, JWST, VLTI and SOFIA, while a wealth of targets is
available from survey work (e.g. VISTA, WISE). In addition it will bring confirmation of the technical readiness and
scientific value of several aspects of potential mid-IR instrumentation at Extremely Large Telescopes.
Accurate calibration of ground-based, mid-infrared observations is challenging due to the strong and rapidly varying thermal background emission. The classical solution is the chopping/nodding technique where the secondary mirror and the telescope are being moved by several tens of arcseconds on the sky. However, chopping is generally inefficient and limited in accuracy and frequency by the mass and size of the secondary mirror. A more elegant solution is a drift scan where the telescope slowly drifts across or around the region of interest; the source moves on the detector by at least one FWHM of the PSF within the time over which the detector performance and the background emission can be considered stable. The final image of a drift scan is mathematically reconstructed from a series of adjacent short exposures. The drift scan approach has recently received a lot of interest, mainly for two reasons: first, some of the new, large-format mid-IR Si:As detectors (AQUARIUS) suffer from excess low frequency noise (ELFN). To reach the nominal performance limit of the detectors, chopping would have to be performed at a high frequency, faster than what most telescopes can handle; second, the next generation of extremely large telescopes will not offer chopping/nodding, and alternative methods need to be developed and tested. In this paper we present the results from simulated drift scan data. We use drift scanning to simultaneously obtain an accurate detector flat field and the sky background. The results are relevant for the future operation and calibration of VISIR at the VLT as well as for METIS, the thermal infrared instrument for the E-ELT.
We present an overview of the VISIR upgrade project. VISIR is the mid-infrared imager and spectrograph at ESO’s
VLT. The project team is comprised of ESO staff and members of the original VISIR consortium: CEA Saclay and
ASTRON. The project plan is based on input from the ESO user community with the goal of enhancing the scientific
performance and efficiency of VISIR by a combination of measures: installation of improved hardware, optimization of
instrument operations and software support. The cornerstone of the upgrade is the 1k by 1k Si:As Aquarius detector
array (Raytheon) which has demonstrated very good performance (sensitivity, stability) in the laboratory IR detector test
facility (modified TIMMI 2 instrument). A prism spectroscopic mode will cover the N-band in a single observation. New
scientific capabilities for high resolution and high-contrast imaging will be offered by sub-aperture mask (SAM) and
phase-mask coronagraphic (4QPM/AGPM) modes. In order to make optimal use of favourable atmospheric conditions a
water vapour monitor has been deployed on Paranal, allowing for real-time decisions and the introduction of a userdefined
constraint on water vapour. Improved pipelines based on the ESO Reflex concept will provide better support to
astronomers. The upgraded VISIR will be a powerful instrument providing background limited performance for
diffraction-limited observations at an 8-m telescope. It will offer synergy with facilities such as ALMA, JWST, VLTI
and SOFIA, while a wealth of targets is available from survey work (e.g. VISTA, WISE). In addition it will bring
confirmation of the technical readiness and scientific value of several aspects of potential mid-IR instrumentation at
Extremely Large Telescopes. The intervention on VISIR and installation of hardware has been completed in July and
commissioning will take place during July and August. VISIR is scheduled to be available to the users starting Oct 2012.
We recall the design and present the development status of GRAAL, the Ground-layer adaptive optics assisted by Laser,
which will deliver wide-field (10 arcmin), enhanced images to the HAWK-I instrument on the VLT, with an improved
seeing. GRAAL is an adaptive optics module, part of the Adaptive optics facility (AOF), using four Laser- and one
natural guide-stars to measure the turbulence, and correcting for it by deforming the adaptive secondary mirror of a Unit
telescope in the Paranal observatory.
GRAAL is in the laboratory in Europe and the integration of its laser guide-star optics is completed. The first wave-front
sensor camera will be ready for its integration in the coming weeks, allowing the first system tests to start.
The ESO's VLT Spectrometer and Imager for the Mid-Infrared (VISIR) has been in operation at the Paranal
Observatory since 2005. It is equipped with two DRS (formerly Boeing) 256 × 256 BIB arrays. The project to
replace detectors into new Raytheon, 1k × 1k AQUARIUS devices as well as to modify observing modes, software,
etc. is underway. The VISIR upgrade creates a well defined break point in the instruments' characteristics. For
nearly 7 years of the VISIR operations we have been collecting and processing calibration data, in particular
observations of the imaging and spectroscopic standard stars, within a regular data flow operation scheme. The
derived quality control parameters have been systematically written into a database, which allows the analysis
of their temporal behavior. We present an overview of the long term variations of the VISIR quality control
parameters: sensitivity, conversion factor and mean background level estimations. The results will be later used
to compare performance of VISIR before and after the upgrade.
We describe the design and development status of GRAAL, the
Ground-layer adaptive optics assisted by Laser, which
will deliver enhanced images to the Hawk-I instrument on the VLT. GRAAL is an adaptive optics module, part of AOF,
the Adaptive optics facility, using four Laser- and one natural
guide-stars to measure the turbulence, and correcting for it
by deforming the adaptive secondary mirror of a Unit telescope in the Paranal observatory.
The outstanding feature of GRAAL is the extremely wide field of view correction, over 10 arcmin diameter, with an
image enhancement of about 20% in average in K band. When observing GRAAL will provide FWHM better than 0.3"
40% of the time. Besides the Adaptive optics facility deformable mirror and Laser guide stars, the system uses subelectron
L3-CCD and a real-time computing platform, SPARTA.
GRAAL completed early this year a final design phase shared internally and outsourced for its mechanical part by the
Spanish company NTE. It is now in manufacturing, with a first light in the laboratory planned in 2011.
The European Southern Observatory (ESO) is preparing to upgrade VISIR, the mid-IR imager and spectrograph at the
VLT. The project team is comprised of ESO staff and members of the original consortium that built VISIR: CEA Saclay
and ASTRON. The goal is to enhance the scientific performance of VISIR and to facilitate its use by the ESO
community. In order to capture the needs of the user community, we collected input from the users by means of a webbased
questionnaire. In line with the results of the internal study and the input from the user community, the upgrade
plan calls for a combination measures: installation of improved hardware, optimization of instrument operations and
software support. The limitations of the current detector (sensitivity, cosmetics, artifacts) have been known for some
time and a new 1k x 1k Si:As Aquarius array (Raytheon) will be the cornerstone of the VISIR upgrade project. A
modified spectroscopic mode will allow covering the N-band in a single observation. Several new scientific modes (e.g.,
polarimetry, coronagraphy) will be implemented on a best effort basis. In addition, the VISIR operational scheme will be
enhanced to ensure that optimal use of the observing conditions will be made. Specifically, we plan to provide a means
to monitor precipitable water vapour (PWV) and enable the user to specify it as a constraint set for service mode
observations. In some regions of the mid-IR domain, the amount of PWV has a fundamental effect on the quality of a
given night for mid-IR astronomy. The plan also calls for full support by ESO pipelines that will deliver science-ready
data products. Hence the resulting files will provide physical units and error information and all instrumental signatures
will have been removed. An upgraded VISIR will be a powerful instrument providing diffraction-limited performance at
an 8-m telescope. Its improved performance and efficiency as well as new science capabilities will serve the needs of the
ESO community but will also offer synergy with various other facilities such as ALMA, JWST, VLTI and SOFIA. A
wealth of targets for detailed study will be available from survey work done by VISTA and WISE. Finally, the upgraded
VISIR will also serve as a pathfinder for potential mid-IR instrumentation at the European Extremely Large Telescope
(E-ELT) in terms of technology as well as operations.
METIS is a mid-infrared instrument proposed for the European Extremely Large Telescope. It is designed to provide imaging and spectroscopic capabilities in the 3 - 14 micron region up to a spectral resolution of 100000. One of the novel concepts of METIS is that of a high-resolution integral field spectrograph for a diffraction-limited mid-IR instrument. While this concept has many scientific and operational advantages over a long-slit spectrograph, one drawback is that the spectral resolution changes over the field of view. This has an impact on the procedures to correct for telluric absorption lines imprinted on the science spectra. They are a major obstacle in the quest to maximize spectral fidelity, the ability to distinguish a weak spectral feature from the continuum. The classical technique of division by a standard star spectrum, observed in a single IFS spaxel, cannot simply be applied to all spaxels, because the spectral resolution changes from spaxel to spaxel. Here we present and discuss possible techniques of telluric line correction of METIS IFS spectra, including the application of synthetic model spectra of telluric transmission, to maximize spectral fidelity.
METIS is a mid-infrared instrument proposed for the European Extremely Large Telescope (E-ELT). It is designed to
provide imaging and spectroscopic capabilities in the 3μm to 14μm region up to a spectral resolution of 100.000. Here
the technical concept of METIS is described which has been developed based on an elaborated science case which is
presented elsewhere in this conference.
There are five main opto-mechanical modules all integrated into a common cryostat: The fore-optics is re-imaging the
telescope focal plane into the cryostat, including a chopper, an optical de-rotator and an un-dispersed pupil stop. The
imager module provides diffraction limited direct imaging, low-resolution grism spectroscopy, polarimetry and
coronagraphy. The high resolution IFU spectrograph offers a spectral resolution of 100.000 for L- and M-band and
optional 50.000 for the N-band. In addition to the WFS integrated into the E-ELT, there is a METIS internal on-axis
WFS operating at visual wavelengths. Finally, a cold (and an external warm) calibration unit is providing all kinds of
spatial and spectral calibrations capabilities. METIS is planned to be used at one of the direct Nasmyth foci available at
This recently finished Phase-A study carried out within the framework of the ESO sponsored E-ELT instrumentation
studies has been performed by an international consortium with institutes from Germany, Netherlands, France, United
Kingdom and Belgium.
We present results of performance modelling for METIS, the Mid-infrared European Extremely Large Telescope
Imager and Spectrograph. Designed by a consortium of NOVA (Netherlands), UK Astronomy Technology Centre
(UK), MPIA Heidelberg (Germany), CEA Saclay (France) and KU Leuven (Belgium), METIS will cover the
atmospheric windows in L, M and N-band and will offer imaging, medium-resolution slit spectroscopy (R~1000-
3000) and high-resolution integral field spectroscopy (R~100,000). Our model uses a detailed set of input
parameters for site characteristics and atmospheric profiles, optical design, thermal background and the most
up-to-date IR detector specifications. We show that METIS will bring an orders-of-magnitude level improvement
in sensitivity and resolution over current ground-based IR facilities, bringing mid-IR sensitivities to the micro-
Jansky regime. As the only proposed E-ELT instrument to cover this entire spectral region, and the only mid-IR
high-resolution integral field unit planned on the ground or in space, METIS will open up a huge discovery space
in IR astronomy in the next decade.
METIS is the 'Mid-infrared ELT Imager and Spectrograph', the only planned thermal/mid-IR instrument for the E-ELT.
METIS will provide diffraction limited imaging in the atmospheric L/M and N-band from 3 - 14 μm over an 18"×18"
field of view (FOV). The imager also includes high contrast coronagraphy and low-resolution (900 ≤ R ≤ 5000) long slit
spectroscopy and polarimetry. In addition, an IFU fed, high resolution spectrograph at L/M band will provide a spectral
resolution of R ~ 100,000 over a 0.4"×1.5" FOV. The adaptive optics (AO) system is relatively simple, and METIS can
reach its full performance with the adaptive correction provided by the telescope - and occasionally even under seeing
limited conditions. On a 42m ELT, METIS will provide state-of-the-art mid-IR performance from the ground. The
science case for METIS is based on proto-planetary disks, characterization of exoplanets, formation of our Solar System,
growth of supermassive black holes, and the dynamics of high-z galaxies. With the focus on highest angular resolution
and highest spectral resolution, METIS is highly complementary to JWST and ALMA. This paper summarizes the
science case for METIS, and describes the instrument concept, performance and operational aspects.
In this paper we present a brief status report on the conceptual designs of the instruments and adaptive optics modules
that have been studied for the European Extremely Large Telescope (E-ELT). In parallel with the design study for the
42-m telescope, ESO launched 8 studies devoted to the proposed instruments and 2 for post-focal adaptive optics
systems. The studies were carried out in consortia of ESO member state institutes or, in two cases, by ESO in
collaboration with external institutes. All studies have now been successfully completed. The result is a powerful set of
facility instruments which promise to deliver the scientific goals of the telescope.
The aims of the individual studies were broad: to explore the scientific capabilities required to meet the E-ELT science
goals, to examine the technical feasibility of the instrument, to understand the requirements placed on the telescope
design and to develop a delivery plan. From the perspective of the observatory, these are key inputs to the development
of the proposal for the first generation E-ELT instrument suite along with the highest priority science goals and
budgetary and technical constraints. We discuss the lessons learned and some of the key results of the process.
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 European Southern Observatory (ESO) is conducting a phase B study of a European Extremely Large Telescope (E-ELT).
The baseline concept foresees a 42m primary, 5 mirror adaptive telescope with two of the mirrors giving the
possibility of very fast correction of the atmospheric turbulence. In parallel to the telescope study, ESO is coordinating
8 studies of instruments and 2 of post-focus Adaptive Optics systems, carried out in collaboration with Institutes in the
member states. Scope of the studies, to be completed by 1Q 2010, is to demonstrate that the high priority scientific goals of
the E-ELT project can be achieved with feasible and affordable instruments. The main observing modes being considered
are: NIR wide field imaging and spectroscopy to the diffraction limit or with partial correction of the atmospheric seeing;
high spectral resolution, high stability visible spectroscopy; high contrast, diffraction limited imaging and spectroscopy; DL
mid-infrared imaging and spectroscopy. The status of the 8 current studies is presented.
The ESO's VISIR instrument at Paranal is dedicated to observations in two mid-infrared (MIR) atmospheric
windows: N-band (8-13 micron) and Q-band (16.5-24.5 micron). It is equipped with two DRS (formerly Boeing)
256 × 256 BIB detectors operating at temperatures of about 5 K. As in case of other Paranal instruments
VISIR data are regularly transferred to ESO Garching within the standard data flow operation. There, they are
classified and pipeline-processed. The products of VISIR technical data are analyzed in order to trend instrument
performance, while calibrations and science data are checked for quality and later distributed to the users. Over
the three years of VISIR operations we have been constantly gaining more experience in methods of assessing
health of the instrument. In particular, we found that dark frames are particularly useful for monitoring the
VISIR detectors. We also discuss performance of the "OCLI" silicate filters recently mounted in the instrument.
The phase A study of a mid infrared imager and spectrograph for the European Extremely Large Telescope (E-ELT), called METIS, was endorsed in May 2008. Two key science drivers of METIS are: a) direct thermal imaging of exo-planets and b) characterization of circumstellar discs from the early proto-planetary to the late
debris phase. Observations in the 10μm atmospheric window (N band) require a contrast ratio between stellar light and emitted photons from the exo-planet or the disc of ~ 105. At shorter wavelengths the contrast between star and reflected light from the planet-disc system exceeds ≳ 107 posing technical challenges. By means of end-to-end detailed simulations we demonstrate that the superb spatial resolution of a 42m telescope in combination with stellar light rejection methods such as coronagraphic or differential imaging will allow detections at 10μm for a solar type system down to a star-planet separation of 0.1" and a mass limit for irradiated planets of 1 Jupiter (MJ) mass. In case of self-luminous planets observations are possible further out e.g. at the separation limit of JWST of ~ 0.7", METIS will detect planets ≳5MJ. This allows to derive a census of all such exo-planets by means of thermal imaging in a volume limited sample of up to 6pc. In addition, METIS will provide the possibility to study the chemical composition of atmospheres of exo-planets using spectroscopy at moderate spectral resolution (λ/Δλ ~ 100) for the brightest targets. Based on detailed performance and sensitivity estimates, we demonstrate that a mid-infrared instrument on an ELT is perfectly suited to observe gravitationally created structures such
as gaps in proto- and post- planetary discs, in a complementary way to space missions (e.g. JWST, SOFIA) and ALMA which can only probe the cold dust emission further out.
Imaging- and spectropolarimetry in the thermal infrared (~ 5-30 μm) can inform us about two important open
questions in modern astrophysics - namely the role of magnetism in the formation of stars, and the life-cycle
of cosmic dust. These are key questions outlined in the document "A Science Vision for European Astronomy"
by de Zeeuw & Molster (2007). Thermal IR polarimetry is the only technique that can peer into the heart of
star forming cores, where an infant star heats its immediate surroundings to temperatures of several hundred
Kelvin. The polarization itself is induced by a preferential alignment of the spin axis of cosmic dust grains, a
process ultimately controlled by the ambient magnetic field. The spectrum is sensitively dependent on the grain
optical properties, structure and shape, thus providing information not otherwise obtainable by conventional
spectroscopy. The MIRI instrument on the JWST will not have a polarimetry mode, thus leaving open the
possibility of an ELT mid-IR instrument being able to make substantial progress on these fundamental issues.
Before describing the advantages of a mid-IR spectropolarimeter on an ELT, we first present some preliminary
results from our polarization observations with the TIMMI2 mid-IR instrument between 2004 and 2006. The
experience gained with TIMMI2 - in terms of technical issues and observing strategy - will inform the design of
any future instrument. Following this we will describe the science that could be done with an ELT instrument,
and some of the basic design parameters. For instance, with a resolution of ~ 70 milli-arcseconds (FWHM at
10 μm) it will become possible to resolve the magnetic field configuration in the circumstellar disks and bipolar
outflows of young stars at a spatial scale of less than 10 AU in the nearest star formation regions. This will
strongly constrain hydromagnetic models - the favoured means of extracting angular momentum and allowing
accretion to proceed - for bipolar jets emanating from a range of compact astrophysical objects. Further, with
a resolving power of order 200, and sensitivity of 100σ in 1 hour integration on a 0.5 mJy point source, the
evolution of cosmic dust - and the governing physical and chemical processes - from its formation in old stellar
outflows to its deposition in planet-forming disks, will become amenable to detailed polarization studies.
VISIR is the VLT mid-infrared (mid-IR) Imager and Spectrometer. Since 2004, it provides data at high spatial
and spectral resolutions in the N (8-13 μm) and Q (16-24 μm) atmospheric windows. VISIR observations have
provided unique constraints on targets such as central regions of nearby galaxies, or protoplanetary disks. We
review here VISIR Imager and Spectrometer characteristics, emphasizing on some current limitations because
of various undesirable effects. Its successor on an ELT will provide data with a unique sharpness (0.05") and
sensitivity (35 μJy source detectable in 1 hour at 10 σ level), thus allowing a characterization of exoplanetary
disks and inner exoplanets with an unprecedent precision. At the light of VISIR experience, we discuss how
the lessons learned from VISIR can be turned to good account for designing and operating the future mid-IR
instrument on the European ELT.
METIS, the Mid-infrared ELT Imager and Spectrograph (formerly called MIDIR), is a proposed instrument for the
European Extremely Large Telescope (E-ELT), currently undergoing a phase-A study. The study is carried out within
the framework of the ESO-sponsored E-ELT instrumentation studies. METIS will be designed to cover the E-ELT
science needs at wavelengths longward of 3μm, where the thermal background requires different operating schemes. In
this paper we discuss the main science drivers from which the instrument baseline has been derived. Specific emphasis
has been given to observations that require very high spatial and spectral resolution, which can only be achieved with a
ground-based ELT. We also discuss the challenging aspects of background suppression techniques, adaptive optics in
the mid-IR, and telescope site considerations. The METIS instrument baseline includes imaging and spectroscopy at the
atmospheric L, M, and N bands with a possible extension to Q band imaging. Both coronagraphy and polarimetry are
also being considered. However, we note that the concept is still not yet fully consolidated. The METIS studies are
being performed by an international consortium with institutes from the Netherlands, Germany, France, United
Kingdom, and Belgium.
CRIRES, a first generation VLT instrument, is a cryogenic high-resolution (R~100,000) IR spectrograph operating in the range 1-5 μm. Here we present a model based wavelength calibration for CRIRES. The procedure uses a streamlined model of the CRIRES optical path that enables calculation of the location of the illumination
in the detector focal plane at sub-pixel accuracy for a given wavelength and instrumental configuration. The instrumental configuration is described in terms of the tips and tilts of optical surfaces, their optical properties and environmental conditions. These parameters are derived through the application of a minimisation algorithm that is capable of using multiple realisations of the model to find the configuration which results in the optimal match between simulated wavelength data and dedicated calibration exposures. Once the configuration is accurately determined the model can be used to provide the dispersion solution for science exposures or to produce two dimensional simulated data for a given spectral source. In addition we describe comparisons to early laboratory data and the optimisation strategy adopted.
VISIR is the new ESO VLT instrument mounted at the Cassegrain focus of Melipal (UT3) telescope. At Paranal it is the very first instrument capable of high sensitivity imaging in the N band and Q band mid infrared atmospheric windows. In addition, it features a long-slit spectrometer with a range of spectral resolutions between 150 and 30000. VISIR had been included in the standard VLT data flow operation even before regular observing started in March/April 2005. Data products are pipeline-processed and quality checked by the Data Flow Operations Group in Garching. The calibration data are processed to create calibration products and to extract Quality
Control parameters. These parameters provide health checks and monitor instrument's performance. They are stored in a database, compared to earlier data, trended over time and made available on the VISIR Quality Control web pages that are updated daily. We present the parameters that were designed to assess quality of the data and to monitor performance of the MIR instrument. We also discuss the general process of data flow and data inspection.
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.
CRIRES is a cryogenic, pre-dispersed, infrared echelle spectrograph designed to provide a resolving power of 105 between 1 and 5 μm at a Nasmyth focus of one of the 8m VLT telescopes. A curvature sensing adaptive optics sytem feed is used to minimize slit losses and a 4096x512 pixel mosaic of Aladdin arrays is being developed to maximixe the free spectral range covered in each order. Insertion of gas cells to measure high precision radial velocities is foreseen and the possibility of combining a Fresnel rhomb with a Wollaston prism for magnetic Doppler imaging is under study. Installation at the VLT is scheduled during the second half of 2004. Here we briefly recall the major design features of CRIRES and describe its current development status.
TIMMI2 ESO's 2nd generation Thermal Infrared Multimode Instrument had astronomical first light in October 2000 at the 3.6 m telescope on La Silla, Chile. Since February 2001 it is in regular use, both by visiting astronomers and in service mode, typically one third of the total telescope time. Using a Raytheon 240 x 320 pixel As:Si-BIB detector allows imaging and grism spectroscopy between 5 and 24 μm. TIMMI2 has also a linear polarimetry mode. We will give a description of the instrument from technical to operational aspects. Because of the substantial gain in sensitivity as compared to previous generation instruments a new set of infrared calibration standards has been constructed. The instrument and telescope are subject of an ongoing sensitivity monitoring program enabling to improve the sensitivity while allowing to spot the development of problems immediately. For stellar objects the sensitivity 10 σ in 1 hour of telescope time is in the range of 15 - 30 mJy. TIMMI2 at the telescope shows negligible flexure (≤ 0.2") while having basically diffraction limited performance for λ ≥ 8 μm.
ESO's Thermal Infrared Multimode Instrument, TIMMI2,in regular operation at the 3.6m telescope on La Silla, Chile,since January 2001 is equipped with a linear polarization mode which can be used in conjunction with all scientific observing modes available. A description of the polarimeter, working between 5 and 24mu m in imaging and low-resolution grism spectroscopy is given. Calibration issues and other operational aspects are described. We report first results from the final astronomical commissioning.
In the so-called parallel mode, ISOCAM, the mid-infrared camera on board ESA's Infrared Space Observatory (ISO), continued to observe while other instruments were prime, thus providing a widespread high-sensitivity survey of the sky. The currently exploitable data set was taken during 7000 hours of observations and consists of over 37000 pointings. The source extraction from these images is a challenging task due to the following difficulties: * the small number of pixels per image (32*32), resulting into a highly under-sampled Point Spread Function * the varying sky area --- from flat background to highly structured or confused * the varying and a priori unknown instrumental noise and the highly varying duration of each pointing * the high number of spurious sources due to restricted glitch-rejection for observations with few readouts * the lack of redundant pointings for the majority of cases The algorithm developed to solve these problems consists of a combination of three detection methods: * sextractor, using various thresholds and convolution files * multi-resolution detection * flux- and position determination of detected sources via modified point-source fitting * heuristic criteria to classify the sources into point- and extended sources