NASA's James Webb Space Telescope

Two for the Price of One: MIRI Simultaneous Imaging

News Feature November 29, 2017

Image showing MIRI simultaneous imaging feature.

The Mid-Infrared Instrument (MIRI) on JWST will open new frontiers in astronomical research by offering unprecedented sensitivity in the 4.9-28.8 micron wavelength range. Four different observing modes are available with MIRI, including imaging and integral field spectroscopy. The Medium-Resolution Spectrometer (MRS) will be used for integral field spectroscopy and has a separate field of view from the imager, allowing for simultaneous operation when the MRS is the primary observing mode. This capability is referred to as simultaneous imaging and is the default choice when specifying MRS observations in APT.

Simultaneous imaging has two primary benefits:

  • More accurate MRS data cube construction. The small field of view of the MRS means that there will be few, if any, stars in the same field of view as the target. Stars are necessary for calculating an absolute astrometric solution needed for accurate alignment of spectra obtained over multiple visits. Large astrometric inaccuracies (~0.5 arcseconds) can be avoided by making simultaneous observations of field stars in the adjacent imager field of view.
  • More data. When using simultaneous imaging, observers have the ability to specify their choice of imaging filter and total exposure time with the imager, as long as it is less than or equal to the total observing time of the primary MRS observation. These choices allow for optimization of potential science observations of the adjacent field with the imager. Examples of science with simultaneous imaging can be found in the list of accepted GTO programs.

NOTE: Simultaneous imaging is not a parallel imaging mode, and can only be specified when the MRS is the primary observing mode.

MIRI simultaneous imaging will be available starting in Cycle 1 for all proposal types (GTO, DD-ERS, GO). Additional information can be found on the simultaneous imaging page in JDox.

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