JWST Mid Infrared Instrument
The JWST Mid-Infrared Instrument (MIRI) provides imaging and spectroscopic observing modes from ~5 to 28μm.
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The JWST Mid-Infrared Instrument (MIRI) provides imaging and spectroscopic observing modes from 4.9 to 27.9 μm. These wavelengths can be utilized for studies including, but not limited to: direct imaging of young warm exoplanets and spectroscopy of their atmospheres; identification and characterization of the first galaxies at redshifts z > 7; and analysis of warm dust and molecular gas in young stars and proto-planetary disks.
To achieve these goals MIRI offers a very broad range of observing modes, including:
- imaging
- low-resolution slitted and slitless spectroscopy
- medium-resolution integral field unit (IFU) spectroscopy
- coronagraphy
Observational capabilities
MIRI offers 4 different observing modes, including (1) imaging with 9 photometric bands, (2) coronagraphic imaging with 4 different filters, (3) low-resolution spectroscopy with a slit or slitless configuration, and (4) medium-resolution spectroscopy with 4 different IFUs. Each mode has its own template in the Astronomer's Proposal Tool (APT). Note that MIRI can also be used effectively for parallel observations with other instruments.
Table 1. Properties of MIRI observing modes
Observing mode | Wavelength | Field of view | Pixel scale | Resolving | FWHM | Notes |
|---|---|---|---|---|---|---|
5.6 to 25.5 μm | 74 × 113 | 0.11 | 3.5 – 16.1 | 2 pix @ 6.25 μm | Subarrays | |
| 10.65, 11.4, 15.5 | 24 × 24 | 0.11 | 14.1 – 17.2 | 2 pix @ 6.25 μm | ||
| 23 | 30 × 30 | 0.11 | 4.1 | 2 pix @ 6.25 μm | ||
5 to 14 μm | 0.51 × 4.7 (slit size) | 0.11 | ~100 @ 7.5 μm | 2.6 pix @ 7.7 μm | Slit or slitless modes | |
4.9 to 27.9 μm | 3.7 to 7.7 | 0.196–0.273 | ~1550–3250 | 2 pix @ 6.2 μm | FWHM = 0.314" × (λ/10 μm) |
Optical elements
Imager
The major optical elements in the MIRI Imager include an 18-station filter wheel, coronagraphic masks, and a single 1k × 1k pixel mid-infrared detector:
- Filter wheel—the 18-station filter wheel includes imaging filters, LRS prism, and coronagraphic filters.
- Coronagraphic masks—in addition to a classical Lyot coronagraph at the telescope focal plane, MIRI incorporates the 4-quadrant phase mask coronagraph technology (4QPM; Rouan et al. 2000) to provide the smallest possible inner working angle (IWA) of ~1λ/D at 10–16 μm.
- Slit—in addition to the coronagraphic masks, the LRS slit is also located at the telescope focal plane.
- Detectors—in contrast to other JWST instruments, which use HgCdTe infrared detector arrays, MIRI uses 3 arsenic-doped silicon (Si:Ar) IBC arrays, each with 1K × 1K pixels. The MIRI detectors were developed specifically for JWST sensitivity requirements; MIRI, being most sensitive to thermal background of all the JWST instruments, is also the coldest instrument, actively cooled to its operating temperature of 7 K by a cryocooler. Since the cryocooler uses a 2-stage closed-cycle design, there is no expendable cryogen.
Medium-resolution spectrometer (MRS)
The major optical elements in the MRS include 2 gratings/dichroic wheels and 4 integral field units (IFUs). The MRS also has 2 mid-infrared detectors of the same type used in the imager.
Sensitivity and performance
Glasse et al. (2015) summarize the approximate sensitivities and saturation limits for various modes obtained from laboratory testing. Observers preparing MIRI proposals should use the JWST ETC to obtain detailed performance estimates (jwst.etc.stsci.edu). Up-to-date information on the use and applicability of the ETC can be found on the ETC website and in the ETC Documentation.
Top: MIRI continuum sensitivity plot for the MRS, LRS, and imager (in black circles) configurations, corresponding to 10-σ in a 10,000 s on-source integration time.
Bottom: MIRI line sensitivity plot for the MRS and LRS (in black), corresponding to 10-σ in a 10,000 s on-source integration time
Note: Sensitivity plots are based on preliminary in-flight measurements obtained during commissioning. The ETC should be used to obtain the most up-to-date numbers.
Data calibration and analysis
Information about calibration is available in the article JWST Data Calibration Considerations; links in the article point to content about absolute astrometric, flux, and wavelength calibration, as well as information on calibration reference files.
Details about the data can be found in the JWST File Names, Format, and Data Structures article. The JWST pipeline is described in JWST Science Calibration Pipeline Overview and some information about post-pipeline processing can be found at JWST Post-Pipeline Data Analysis.
External MIRI links and documents
MIRI "Encyclopedia"
Rieke, G., et al. 2015, PASP, 127, 584
The Mid-Infrared Instrument for the James Webb Space Telescope, I: Introduction
PDF, Univ. of Arizona
Wright, G.S., et al. 2015, PASP, 127, 595
The Mid-Infrared Instrument for the James Webb Space Telescope, II: Design and Build
PDF, Univ. of Arizona
Bouchet, P., et al. 2015, PASP, 127, 612
The Mid-Infrared Instrument for the James Webb Space Telescope, III: MIRIM, The MIRI Imager
PDF, Univ. of Arizona
Kendrew, S., et al. 2015, PASP, 127, 623
The Mid-Infrared Instrument for the James Webb Space Telescope, IV: The Low-Resolution Spectrometer
PDF, Univ. of Arizona
Boccaletti, A., et al. 2015, PASP, 127, 633
The Mid-Infrared Instrument for the James Webb Space Telescope, V: Predicted Performance of the MIRI Coronagraphs
PDF, Univ. of Arizona
Wells, M., et al. 2015, PASP, 127, 646
The Mid-Infrared Instrument for the James Webb Space Telescope, VI: The Medium Resolution Spectrometer
PDF, Univ. of Arizona
Rieke, G. H., et al. 2015, PASP, 127, 665
The Mid-Infrared Instrument for the James Webb Space Telescope, VII: The MIRI Detectors
PDF, Univ. of Arizona
Ressler, M. E., et al. 2015, PASP, 127, 675
The Mid-Infrared Instrument for the James Webb Space Telescope, VIII: The MIRI Focal Plane System
PDF, Univ. of Arizona
Glasse, A., et al. 2015, PASP, 127, 686
The Mid-Infrared Instrument for the James Webb Space Telescope, IX: Predicted Sensitivity
PDF, Univ. of Arizona
Gordon, K. D., et al. 2015, PASP, 127, 696
The Mid-Infrared Instrument for the James Webb Space Telescope, X: Operations and Data Reduction
PDF, Univ. of Arizona
External MIRI websites
UK Astronomy Technology Centre; The Royal Observatory, Edinburgh MIRI Site
University of Arizona MIRI Site
European Space Agency (ESA) MIRI Site
Lectures
JWST Community Lecture Series - The Mid-Infrared Instrument (MIRI) for JWST (G. Rieke)
Acknowledgements
MIRI development was an equal collaboration between European and US partners.
The MIRI optical system was built by a consortium of European partners from Belgium, Denmark, France, Germany, Ireland, the Netherlands, Spain, Sweden, Switzerland, and the United Kingdom. They were led by Gillian Wright, the European Principal Investigator, and Alistair Glasse, Instrument Scientist.
EADS-Astrium (now Airbus Defence and Space) provided the project office and management. The full instrument test was conducted at Rutherford Appleton Laboratory.
The Jet Propulsion Laboratory (JPL) provided the core instrument flight software, the detector system, including infrared detector arrays obtained from Raytheon Vision Systems, collaborated with Northrop Grumman Aerospace Systems on the cooler development and test, and managed the US effort.
The JPL Instrument Scientist is Michael Ressler and the MIRI Science Team Lead is George Rieke.
References
Glasse, A., et al., 2015, PASP, 127, 686
The Mid-Infrared Instrument for the James Webb Space Telescope, IX: Predicted Sensitivity
Updated version
Rieke, G., et al. 2015, PASP, 127, 584
The Mid-Infrared Instrument for the James Webb Space Telescope, I: Introduction
Updated version
Rouan, D., et al. 2000, PASP, 112, 1479
The Four-Quadrant Phase-Mask Coronagraph. I. Principle
Wright, G.S., et al. 2015, PASP, 127, 595
The Mid-Infrared Instrument for the James Webb Space Telescope, II: Design and Build
Updated version