MIRI LRS Mosaics
Mosaics for an LRS observation can be implemented in the Astronomer's Proposal Tool (APT) using the JWST APT MIRI Low Resolution Spectroscopy template. These mosaics provide coverage of larger fields of view (FOV) that extend beyond a single pointing. Mosaics are only supported for observations with the LRS slit; the LRS slitless mode is dedicated to single-pointing time-series observations.
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For mosaics, the number of rows sets the number of steps in the dispersion (cross-slit) direction, while the number of columns sets the number of steps in the cross-dispersion direction (the spatial direction, or along the slit). The mosaic pattern is centered on the coordinates of the specified target. If the user wishes to observe the position pointed to by the target coordinates in the center of the slit (in the dispersion direction), then they should set an odd number of rows. To translate the percentage overlap between pointings into angles on the sky, the user should keep in mind that the slit dimensions are approximately 0.52" in the row direction and 4.7" in the column direction.
Users are strongly encouraged to always check the defined pattern using the APT Aladin visualization functionality, which shows the slit footprints superimposed on the target.
The user should also consider using the MIRI Medium-Resolution Spectrometer (MRS), which provides integral field spectroscopy (IFU) at higher spectral resolution than the LRS (from ~5 to 28.5 µm, albeit without continuous spectral coverage).