MIRI

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Image above: Graphical overview of the MIRI instrument (left) and the MIRI spectrometer (right). © NOVA

MIRI (European Consortium PI Wright), the Mid-InraRed Instrument is a collaborative effort between NASA and ESA to provide mid-infrared imaging and spectroscopy on James Webb Space Telescope (JWST). MIRI consists of a camera and an R ~3000 IFU spectrometer that will operate in the 5−28.5 μm wavelength range. Light from the JWST focal plane is collimated and then split spectrally into four paths by sets of dichroic filters mounted in a wheel. The resulting four passbands are fed into four IFUs where the images are sliced and re-assembled to form the entrance slits for the spectrometers. The light from each IFU is separately collimated and dispersed. The spectra from pairs of gratings are then imaged by two cameras onto two Si:As 1024 x 1024 detector arrays. By arranging two spectral ranges onto each detector simultaneously the efficiency of the spectrometer is doubled. This results in a division of the full 5-28.5 μm range into four equal channels. Full wavelength coverage is obtained in three grating moves using a single grating wheel mechanism.

The main science drivers of MIRI are:

1) High redshift galaxies: MIRI is the key instrument for distinguishing true ‘first light’ galaxies from galaxies with more evolved stellar populations and to quantify the stellar mass density-star formation relation at high redshifts;

2) Protostars: MIRI will probe the physics of shocks and disk formation close to the growing star and will make an inventory of ices, including the more complex species for the first time;

3) Protoplanetary disks: MIRI will uniquely probe the chemistry and physics in the inner terrestrial planet-forming zones of disks;

4) Exoplanetary atmospheres: all JWST instruments, including MIRI, will highlight observations of exoplanetary atmospheres (transit, eclipse) down to the super-Earth masses.

MIRI will be three orders of magnitude more sensitive than any existing ground-based instrument in the 5−30 μm range, a large part of which (>50 %) is completely blocked by atmospheric features from the ground. Compared with Spitzer (85 cm space telescope), MIRI will have more than an order of magnitude increase in sensitivity and almost an order of magnitude increase in spatial resolution. Moreover, its R~3000 spectral resolving power is much higher than that of Spitzer. MIRI complements Herschel and ALMA, which observe(d) at wavelengths >50 μm.

During 2002-2009, the Netherlands constructed the Spectrometer Main Optics (SMO) of the MIRI. In 2010-2012, the Flight Module (FM) has been integrated, tested and delivered to ESA and NASA. After instrument delivery in May 2012, the MIRI European Consortium (EC) continues to be responsible for the instrument and is contractually required to deliver major parts of the instrument characterization and calibration, support Integrated Science Instrument Module (ISIM) testing, and co-lead software development and mission preparation.

The Dutch MIRI team has played an important role in the MIRI consortium during all of the project phases, from making the initial science case and conception of the instrument to the design and development of the SMO by the NOVA Op-IR instrumentation Group, support of the instrument tests at Rutherford Appleton Laboratory and the analysis of the test data, to leading the MIRI EC software development and supporting mission preparation at STScI (the JWST operations center). During the design phase the Dutch team has been instrumental in safeguarding the spectroscopic capabilities of MIRI and is now the driving force in exploiting the unique science potential of the integral field unit (IFU) spectrometer within the EC. The Dutch MIRI team aims to maintain its strong role in the continued MIRI EC activities. In particular, the NL co-leads the EC software developments and IFU characterization and is heavily involved in the preparation of the MIRI GTO science program.

The NOVA principal investigator for MIRI is Prof. dr. Ewine van Dishoeck (Leiden observatory).

Image below: MIRI optical module being integrated into the Integrate Science Instrument Module (ISIM). Credit: NASA

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