Mid Infrared Instrument

The JWST Mid-Infrared Instrument (MIRI) provides imaging and spectroscopic observing modes from 4.9 to 28.8 μm.  



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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: 

Figure 1. JWST MIRI field of view in the telescope focal plane

MIRI FOV in the telescope focal plane



Observational capabilities

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

Observing mode

Wavelength
coverage 
(μm)

Field of view
or slit size
(arcsec)

Pixel scale
("/pixel)

Resolving
power
R = λ/Δλ

FWHM
 

Comment

Imaging

5–28

74 × 113

0.11n/a2 pix @ 6.25 μm

Subarrays
available
FWHM = 2 pix × (λ/6.25 μm)
for λ > 6.25 μm

4QPM coronagraphic Imaging

10.65, 11.4, 15.5

24 × 24

0.11n/a2 pix @ 6.25 μm


Lyot coronagraphic Imaging

2330 × 300.11n/a2 pix @ 6.25 μm

Low-resolution spectroscopy

5–12

0.51 × 4.7 (slit size)

0.11

~100 @ 7.5 μm

2.6 pix @ 7.7 μm

Slit or slitless modes

Medium-resolution spectroscopy

4.9–28.8

3.9 to 7.7

0.196–0.273~1550–32502 pix @ 6.2 μm

FWHM = 0.314" × (λ/10 μm)
for λ > 8 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 masksin 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.

Figure 2. Optical elements and optical path for the MIRI imager


Figure 3. MIRI imaging filter curves


Figure 4. MIRI coronagraphic imaging filter curves


Medium-resolution spectrometer (MRS)

The major optical elements in the MRS include two gratings/dichroic wheels and four integral field units (IFUs). The MRS also has two mid-infrared detectors of the same type used in the imager.

Figure 5. Optical elements and optical path for the MIRI MRS


Figure 6. MIRI MRS IFU channels



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.

Figure 7. MIRI sensitivity plot for various instrument modes
MIRI sensitivity plot for MRS (in colors), LRS (in black), and imager (in circles) configurations, corresponding to 10-σ in a 10,000 s on-source integration time. 


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 astrometricflux, 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

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

STScI MIRI Website

UK Astronomy Technology Centre; The Royal Observatory, Edinburgh MIRI Site

University of Arizona MIRI Site

NASA MIRI Site 

European Space Agency (ESA) MIRI Site

Lectures

JWST Community Lecture Series - The Mid-Infrared Instrument (MIRI) for JWST (G. Rieke)

Other documents

JWST Pocket Guide

JWST technical documents



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




Published

 

Latest updates

  • Updated sensitivity graph to reflect values that are currently used