MIRI (the Mid InfraRed Instrument) is one of the focal plane instruments of the James Webb Space Telescope. The instrument comprises a camera and a spectrometer module. The instrument plays the following key roles in the JWST science program. - Discovery of the “first light”. - Assembly of galaxies: history of star formation, growth of black holes, production of heavy elements. - Formation of stars and planetary systems. - Evolution of planetary systems and conditions for life. The MIRI spectrometer covers the spectral range from 5 – 28.3 μm with a spectral resolution better than 2000. The spectral module is an imaging spectrometer with a field of view ≥ 3 arcsec. The spectrometer consists of 4 spectral channels that share 2 detectors of 1024 × 1024 pixels each. In a single measurement one third of the wavelength range of the channels is imaged onto the detectors. By changing gratings the whole spectral range is covered in 3 measurements. In this paper the optical design of the MIRI spectrometer is described.
MIRI ('Mid Infrared Instrument') is the combined imager and integral field spectrometer for the 5-29 micron wavelength
range under development for the JWST. The Spectrometer Main Optics (SMO) system has been designed on the basis of
a 'no adjustments' philosophy. This means that the optical alignment precision depends strongly on the design, tolerance
analysis and detailed knowledge of the manufacturing process. Because in principle no corrections are possible after
assembly, continuous tracking of the alignment performance during the design and manufacturing phases is important.
This is done by controlling the "alignment budget" which allows a detailed comparison of the required and achieved
alignment from component to system level. This paper will describe the development of the SMO alignment budget, and
how it is used to bring the alignment performance under control. In addition, we will discuss the results of the actual
alignment measurements on the SMO hardware and the feedback of these results into the alignment budget.
The MIRI Medium Resolution Spectrometer (MIRI-MRS) will increase the sensitivity of astronomical spectroscopy at thermal infrared wavelengths (from 5 to 28 microns), by a factor of 1000 over the best that can be achieved by existing ground-based instruments. This leap in performance is further enhanced by the first use at these wavelengths of all reflective Integral Field Units (image slicers) to provide the spectrometer with a rectangular field of view with a shortest dimension of 3.5 arcseconds.
We describe the optical design of the MRS and present predictions for its delivered image quality.
VISIR is the mid-infrared instrument installed in 2004 at the Cassegrain focus of MELIPAL, one of the four 8-meter telescopes of the European Very Large Telescope program. This cryogenic instrument, optimized for diffraction-limited performances in both mid-infrared atmospheric windows (N and Q bands), combines imaging capabilities and long-slit grating spectroscopy with spectral resolutions up to R=25000 at 10 μm and 12500 at 20 μm. The contract to design and build VISIR was signed in November 1996 between the European Southern Observatory (ESO) and a French-Dutch consortium of institutes led by Service d'Astrophysique of Commissariat a l'Energie Atomique (CEA). After extensive tests in the laboratory, VISIR was shipped to Paranal in March 2004. After successful commissioning between May and August 2004 and science verification between September 2004 and January 2005, routine science operations started in April 2005. The status of VISIR after 2 years of operation at the telescope is reviewed. This complex instrument, which features 14 cryogenic actuators to set the various observing possibilities, has been working without technical failure. The on-sky sensitivities are close to expectations. The median seeing conditions at Paranal (about 0.8-0.9 arcsec in the visible) are an issue to get routinely diffraction-limited images. Simple tip tilt adaptative corrections would be needed. For bright enough sources (a few Jansky), the so-called "burst mode", which allows to store up to 1500 individual frames (10-50 ms each) can be used to retrieve, off-line, diffraction-limited angular resolution (0.3 arcsec at 10 microns).
In December 2004 the European Consortium that develops the optical bench assembly for MIRI successfully passed the Preliminary Design Review. MIRI is the combined imager and integral field spectrometer for the 5-28 micron wavelength range under development for the JWST. After this PDR milestone the optical design of the MIRI spectrometer is now implemented in a compact, modular mechanical design that puts all optical elements in place within the required tolerances. Many aspects of this design are based on the heritage of previous instruments developed at ASTRON, in particular the cryogenic optics for the mid-IR VLT instruments VISIR and MIDI, but several adjustments
to this design philosophy were made to develop the necessary space-qualified light-weighted components. Prototyping of these components has now started. This paper describes trade-offs and solutions for the opto-mechanical design of the optics (gratings, mirrors and their mountings) and of the main structure of the spectrometer, taking into account optical performance, manufacturability, cost and lead times. It also addresses the complex interface management in a large international consortium and reports first prototype results.
In this paper, we present the status of VISIR, the mid-infrared instrument to be installed in 2003 at the Cassegrain focus of MELIPAL, one of the four 8-meter telescopes of the European Very Large Telescope. This cryogenic instrument, optimized for diffraction-limited performance in both mid-infrared atmospheric windows (N and Q band), combines imaging capabilities over a field up to about 1x1 arcmin<sup>2</sup>, and long-slit (0.5 arcmin) grating spectroscopy with various spectral resolutions up to R=25000 at 10 μm and 12500 at 20 μm. The contract to design and build VISIR was signed in November 1996 between the European Southern Observatory (ESO) and a French-Dutch consortium of institutes led by Service d'Astrophysique of Commissariat l'Energie Atomique (CEA). A key step in the project has been passed in December 2001, with the first infrared images in the laboratory and in April 2002 with the first infrared spectra in the laboratory. We present the results of the laboratory tests of the instrument, which is scheduled to be shipped to Paranal at the end of 2002.
Since the beginning of the VISIR project, the calibration aspects have been taken into account as an integral part of the design. In order to provide the user and the archive with high quality and well-controlled data, it is mandatory to have, during the routine observation phase, all calibration observations as part of the instrument set-up activities and as part of the actual Astronomical Observing Template. We propose here to review the calibration of VISIR observations. After a description of the various hardware
tools which have been introduced for calibration purposes (warm calibration unit, distortion grid, pupil imaging optics, wavelength calibration modules), we will present the calibrations in four astronomical categories (spatial resolution, photometry, astrometry and wavelength calibration). Cross-calibrations between the Imager and Spectrometer subsystems will also be addressed.
MIRI, the mid-IR instrument for NGST is being provided by a collaboration between a consortium of European institutes, ESA, NASA, JPL and US scientists, with the Europeans responsible for the optics module. The instrument will provide diffraction limited imaging and spectroscopic capability over the 5-28μm region with unprecedented sensitivity. In this paper we describe the current optical design of the medium resolution spectroscopy channel (MIRI-S). This uses a novel arrangement of dichroics, image slicers and spectrometers to optimise the division of a limited number of detector pixels between spatial and spectral information whilst working within the tight mass and volume constraints imposed by a space mission. We also present our design for reflective image slicers that are adapted properly for diffraction limited performance to provide a high throughput over the full wavelength range of the instrument.
MIDI is the Mid-Infrared interferometer for ESO's VLTI (Very Large Telescope Interferometer), which has been developed by a German-Dutch-French consortium [MPIA Heidelberg Germany, NOVA/ASTRON Dwingeloo Netherlands, Observatoire de Meudon France]. The initial aim of MIDI is to combine the beams from 2 telescopes in the 10 micron N-band with a spatial resolution of up to 10 milli-arcseconds and a maximum spectral resolution of 230. Modulation of the optical path difference can be done using piezo-driven mirrors at room temperature, but beam combination and detection of the interferometric signal has to be done at cryogenic temperatures due to the 'thermal' wavelength domain. The MIDI cold bench is therefore mounted inside a cryostat, cooled by means of a closed cycle cooler to about 40K for the cold optics and 8K for the detector.
The design of the cold optics has been kept as simple as possible, creating challenges such as preserving alignment from 295K to 40K and accessibility. This poster describes the realization of the cold optics, the alignment and test strategies and laboratory results.
The first science instrument for the Very Large Telescope Interferometer (VLTI), the Mid-infrared instrument MIDI, will be commissioned in November 2002 with anticipated first fringe during that commissioning run on the 40-cm Siderostats and the 8.2-meter Unit Telescopes. In this paper we describe scientific and technical observing modes (also referred to as observation procedures) developed for MIDI and discuss in detail how an observing run with the instrument is planned.
MIDI is built by a consortium lead by the Max Planck Institute for Astronomy (MPIA Heidelberg), with contributions from among others ASTRON (Dwingeloo, The Netherlands), Leiden Observatory, University of Amsterdam, Paris Observatory, University of Groningen, the Kiepenheuer-Institut fur Sonnenpysik at Freiburg, Thuringer Landessternwarte Tautenburg, and the Observatoire de la Cote d'Azur.
In this paper, we present the status of VISIR, the mid-IR instrument to be installed in 2001 at the Cassegrain focus of YEPUN, the telescope unit number 4 of the European Very Large Telescope program. This cryogenic instrument, optimized for both mid-IR atmospheric windows, combines imaging capabilities over a field up to about 1 arcmin at the diffraction limit of the telescope, and long-slit grating spectroscopy capabilities with various spectral resolution up to 25000 at 10 micrometers at 20 micrometers . The contrast to design and build VISIR was signed in November 1996 between the European Southern Observatory and French-Dutch consortium of institutes led by Service d'Astrophysique of Commissariat a l'Energie Atomique. A key step in the project has been passed in 1999: the final design review. The instrument is now in the manufacture phase. Several subsystems have already been built and tested. The integration of the whole instrument is scheduled to start in December 2000.
ESO's new Very Large Telescope will consist of four 8.2 m telescopes and three moveable 1.8 m telescopes. Light from these can be combined in the Very Large Telescope Interferometer (VLTI) providing milli-arcsecond resolution with high sensitivity. The VLTI will first operate in the infrared and will produce first fringes in 2001. MIDI is the VLTI instrument for interferometry in the mid-infrared (10 - 20 microns) and is under development by a German-Dutch- French consortium. The initial aim of MIDI is to combine the beams of two telescopes in the 10 micron `N-band' and to achieve spatial resolutions of 20 milli-arcseconds at a spectral resolution of 200 - 300. Modulation of the optical path difference can be done using piezo-driven mirrors at room temperature, but beam combination and detection of the interferometric signal has to be done at cryogenic temperatures due to the `thermal' wavelength domain. The MIDI cold bench is therefore mounted inside a cryostat, cooled by means of a closed cycle cooler to about 40 K for the cold optics and 8 K for the detector. This poster describes the design and implementation of the MIDI cold bench.
We describe principles, design and present status of MIDI, the mid-infrared interferometric instrument for the VLTI, which is planned to come into operation at the ESO Very Large Telescope Interferometer during the second half of 2001.
In this paper, we present VISIR, the mid-IR instrument to be installed in 2001 on the telescope unit number 3 or the European Very Large Telescope program. The instrument combines imaging capabilities over a field up to about 1 arcmin at the diffraction limit of the telescope, and long- slit grating spectroscopy capabilities with various spectral resolutions. The contract to design and build VISIR was signed in November 1996 between ESO and a French-Dutch consortium of institutes. One year after the signature of the contract, VISIR has successfully passed the preliminary design review. The results of the first year of studies are presented here.Emphasis is put on the optical design which is in its final form.
In 1992, the European Southern Observatory (ESO) committed a phase A study of a mid- infrared instrument for the 2nd unit VLT telescope, to a consortium of laboratories (SAp at Saclay, France; SRON at Groningen, Germany; and the Kapteyn Observatory at Roden, Netherlands). The results of the study are presented. One key scientific objective for this instrument is foreseen to be the study of dust. The required observing modes are (1) diffraction limited imaging both at 10 and 20 microns, and (2) spectroscopy at low resolution (R approximately equals 500) both at 10 and 20 microns. Another key domain is the study of atomic, molecular, and ionic lines observable in the atmospheric window at 10 and 20 microns. Given the various environments where the lines originate, medium (approximately equals 5000) to high (approximately equals 30,000) spectral resolution is needed. The optical design, as well as a mechanical layout, incorporating the various modes is described. The imaging and spectroscopic channels are separated. The spectrometer is based on a long slit all reflective design. Two optical configurations have been studied in detail. Because of the need for variable magnifications, the imager is based on refractive optics.