NIRCam Subarray Primary Dithers
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Moreover, during launch, the first fold mirror in the NIRCam short wavelength channel on module B underwent a very small motion (expected from ground tests) which serendipitously improved the overlap between the short and long wavelength channels. In addition, the NIRCam team redefined the spatial location of the SUB64P subarray (and the SUB160P as well) on the B1 and B5 detectors, to make them concentric.
For all the reasons above, the usefulness of the SUBARRAY_DITHER primary dither pattern is greatly reduced, and this type of dither may be discontinued in the future. Currently, the dither pattern is still offered, but the NIRCam team recommends using the subpixel dither type STANDARD pattern instead, to better sample the PSF while still mitigating detector defects.
See also: NIRCam Dithers and Mosaics
Table 1. SUBARRAY_DITHER positions
Position | Offsets (arcsec) | |
---|---|---|
# | X | Y |
1 | -0.335 | -0.335 |
2 | +0.335 | +0.335 |
3 | -0.295 | +0.295 |
4 | +0.295 | -0.295 |
References
Rigby, J. et al 2022, eprint arXiv:2207.05632
Characterization of JWST science performance from commissioning