The JWST Mid-Infrared Instrument (MIRI) provides dithering capabilities for the imaging, low-resolution spectroscopy, medium-resolution spectroscopy, and coronagraphic imaging modes for optimal sampling, bad pixel mitigation, and background subtraction.
When using MIRI, dithering is required to achieve accurate photometry and to provide superior sampling (Arendt et al. 2000). Dither patterns for MIRI have been designed to account for the fact that telescope motions larger than ~20" typically result in new guide star acquisitions and larger observing overheads. The fine steering mirror (FSM) can be used for subpixel (≤50 mas) offsets, which will be used primarily for coronagraphy. Larger dithers are accomplished by moving JWST.
Dithers and mosaics are distinct in terms of operational ordering. All dither positions must be executed before filter changes may be executed. All filter changes are executed before proceeding to the next tile in a mosaic.
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- Imaging dithers
- Coronagraph imaging dithers: Spacecraft roll dithering & small grid dithers for phase diversity
- Low-resolution spectroscopy dithers: Mapping and Along Slit Nod
- Medium-resolution spectroscopy dithers
- Dithering with JWST
Arendt, R. G., et al., 2000, ApJ, 536, 500
Dithering Strategies for Efficient Self-Calibration of Imaging Arrays