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: 

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

MIRI FOV in the telescope focal plane



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
coverage 
(μm)

Field of view
or slit size
(arcsec)

Pixel scale
("/pixel)

Resolving
power
R = λ/Δλ

FWHM
 

Notes

Imaging

5.6 to 25.5 μm

74 × 113

0.113.5 – 16.12 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

0.1114.1 – 17.22 pix @ 6.25 μm


Lyot coronagraphic Imaging

2330 × 300.114.12 pix @ 6.25 μm

Low-resolution spectroscopy

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

Medium-resolution spectroscopy

4.9 to 27.9 μm

3.7 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 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.

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

Click on the figure for a larger view.

© MIRI Team/University of Arizona

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 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.

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

Click on the figure for a larger view.

© MIRI Team/University of Arizona

Figure 6. MIRI MRS IFU channels

Figure credit: STScI MIRI Team


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

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 Calibration Status; 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 Science Data Overview article. The JWST pipeline is described in JWST Science Calibration 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

Wright, G.S., et al. 2015, PASP, 127, 595
The Mid-Infrared Instrument for the James Webb Space Telescope, II: Design and Build

Bouchet, P., et al. 2015, PASP, 127, 612
The Mid-Infrared Instrument for the James Webb Space Telescope, III: MIRIM, The MIRI Imager

Kendrew, S., et al. 2015, PASP, 127, 623
The Mid-Infrared Instrument for the James Webb Space Telescope, IV: The Low-Resolution Spectrometer

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

Wells, M., et al. 2015, PASP, 127, 646
The Mid-Infrared Instrument for the James Webb Space Telescope, VI: The Medium Resolution Spectrometer

Rieke, G. H., et al. 2015, PASP, 127, 665
The Mid-Infrared Instrument for the James Webb Space Telescope, VII: The MIRI Detectors

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

Glasse, A., et al. 2015, PASP, 127, 686
The Mid-Infrared Instrument for the James Webb Space Telescope, IX: Predicted Sensitivity

Gordon, K. D., et al. 2015, PASP, 127, 696
The Mid-Infrared Instrument for the James Webb Space Telescope, X: Operations and Data Reduction

External MIRI websites

STScI MIRI Website

UK Astronomy Technology Centre; The Royal Observatory, Edinburgh 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)



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

Rieke, G., et al. 2015, PASP, 127, 584
The Mid-Infrared Instrument for the James Webb Space Telescope, I: Introduction

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




Notable updates
  •  
    Updated PCE plots (Figures 3, 4, 6).

  •  
    Updated based on in-flight measurements


  • Updated sensitivity graph to reflect values that are currently used
Originally published