The JWST Mid-Infrared Instrument (MIRI) provides target acquisition capabilities for the low-resolution spectroscopy, medium-resolution spectroscopy, and coronagraphic imaging modes.

Target acquisition (TA) is a procedure that centroids a source and places it accurately within an aperture, region of interest (ROI), or subarray. The filters available for MIRI TA are F560W, F1000W, F1500W, and FND. 

TA procedures in the Astronomer's Proposal Tool (APT) are available in these articles:

• MIRI LRS Slit Target Acquisition
• MIRI LRS Slitless Target Acquisition
• MIRI MRS Target Acquisition
• MIRI Coronagraphic Imaging Target Acquisition

MIRI target acquisition readout patterns.

See also: Understanding Exposure Times

The target acquisition process requires the target acquisition file to be stored on-board. Since on-board memory can only store the equivalent of 10 full frame groups of MIRI data at a time, target acquisition in un-grouped FAST mode is limited to a maximum exposure time that might be shorter than desired by the user.  

The FAST readout mode and the FASTGRPAVG series of readout modes are available for MIRI target acquisition only. The FASSTGRPAVG readout modes allow for longer exposure times. This is done by averaging a given number of MIRI frames together in the ISIM FPAP (Focal Plane Array Processor) as a group. Note that all MIRI target acquisition exposures use one integration.

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