NIRISS AMI Calibration Status
The overall calibration status and estimated accuracy of NIRISS aperture masking interferometry are described in this article; please also see the article on known issues affecting NIRISS AMI data.
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Astrometric calibration
Date:
This is the same as for imaging; see NIRISS Imaging Calibration Status.
Photometric calibration
Date:
A range of about 5% in the scaling factors from different standard stars is observed in the F277W/F380M/F430M filters, and the range is 8% for F480M. The uncertainty in the relative calibration of the normal imaging and AMI imaging modes is under 1%.
Calibration of charge migration (CM)
Date:
Commissioning characterized the largest CM effect on the order of a ~1% drop in the count rate between the first half of an exposure and the second half (using 3 groups and a peak pixel with 30,000 e– accumulated charge). A charge migration mitigation step has been implemented in the operational JWST pipeline for NIRISS data (v10.0, released Dec 5, 2023). Quantification of the improvement is being assessed.
Target placement
Date:
An approximately 0.03 pixel standard deviation per axis random error in AMI target placement was measured in the AMI medium band filters during commissioning.
Commissioning data revealed systematic filter-specific offsets from commanded positions (20 mas for F380M, 12 mas for F430M, and 14 mas for F480M). Updated Science Instrument Aperture File (SIAF) definitions were installed onboard to remove these systematic target placement errors. These updates have not been tested yet.