Mid Infrared Instrument
The JWST Mid-Infrared Instrument (MIRI) provides imaging and spectroscopic observing modes from 4.9 to 28.8 μm.
The JWST Mid-Infrared Instrument (MIRI) provides imaging and spectroscopic observing modes from 4.9 to 28.8 μm (Wright et al. 2015, Rieke et al. 2015). 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:
- low-resolution slitted and slitless spectroscopy
- medium-resolution integral field unit (IFU) spectroscopy
MIRI offers four different observing modes, including (1) imaging with nine photometric bands, (2) coronagraphic imaging with four different filters, (3) low-resolution spectroscopy with a slit or slitless configuration, and (4) medium-resolution spectroscopy with four 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
Field of view
74 × 113
|0.11||n/a||2 pix @ 6.25 μm|
|10.65, 11.4, 15.5|
24 × 24
|0.11||n/a||2 pix @ 6.25 μm|
|23||30 × 30||0.11||n/a||2 pix @ 6.25 μm|
0.51 × 4.7 (slit size)
~100 @ 7.5 μm
|2.6 pix @ 7.7 μm|
Slit or slitless modes
3.9 to 7.7
|0.196–0.273||~1550–3250||2 pix @ 6.2 μm|
FWHM = 0.314" × (λ/10 μm)
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 three 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 two-stage closed-cycle design, there is no expendable cryogen.
Medium-resolution spectrometer (MRS)
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.
Data calibration and analysis
Information about calibration is available at Data Processing and Calibration Files. This article and its links 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 Data Reduction Pipeline and some information about post-pipeline processing can be found at JWST Post-Pipeline Data Analysis.
External MIRI links and documents
External MIRI websites
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.
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.
Rouan, D. et al. 2000, PASP, 112, 1479
The Four-Quadrant Phase-Mask Coronagraph. I. Principle