The calwebb_ami3 module is stage 3 of the JWST Science Calibration Pipeline for NIRISS aperture masking interferometry (AMI) data. The inputs to this stage are the calibrated slope images (calwebb_image2 output) and the output is interferometric observables. The steps are listed in Figure 1 with the flow from the top to the bottom.

A brief description of each of the steps within calwebb_ami3 can be found below, along with links to further details (e.g., the relevant reference files) that can be found on the corresponding ReadTheDocs pages. Note, however, that the reference files themselves are all provided via CRDS. For instrument mode-specific notes on these pipeline steps see the corresponding known issues with JWST data articles.

Starting with pipeline build 10.2, the calwebb_ami3 module uses the "Image Plane approach to Interferometric Analysis" (ImPlaneIA, Greenbaum et al. 2015) algorithm to extract interferometric information. This algorithm fits an analytical model to the data to extract interferometric observables such as fringe phases and fringe amplitudes, closure phases and closure amplitudes and pistons (optical path delays between mask holes). Other interferometric extraction codes are described in Sivaramakrishnan et al. 2023 and compared in Lau et al. 2023.  For further details about AMI-specific processing, see the NIRISS AMI pipeline notes.

Note that the pre-build 10.2 step AMI Average has been deprecated until the effects of averaging multiple exposures has been more thoroughly examined.

Assemble reference PSFs

The available list of reference PSFs is generated. These reference PSFs consist of reference stars specifically observed for the target. Note that this step is in practice taken care of by the association generator, which lists all science and PSF reference inputs to be used by calwebb_ami3 processing.

Calculate observables

ReadTheDocs documentation: AMI Analyze
Package name: ami_analyze

The closure phases and visibilities for each reference PSF and target are calculated. As part of this calculation, the centers of the reference and target PSFs are determined (iteratively).

Normalize observables

ReadTheDocs documentation: AMI Normalize 
Package name: ami_normalize

The reference PSF closure phases are subtracted from the target closure phases. The target visibilities are divided by the reference PSF visibilities. These two calculations are done matched by dither position.

References

Greenbaum, A., Pueyo, L., Sivaramakrishnan, A., Lacour, S., et al., 2015, ApJ, 798, 68
An Image-plane Algorithm for JWST's Non-redundant Aperture Mask Data

Lau, R. M. et al. 2023 arXiv:2311:15948
A First Look with JWST Aperture Masking Interferometry (AMI): Resolving Circumstellar Dust around the Wolf-Rayet Binary WR 137 beyond the Rayleigh Limit

Sivaramakrishnan, A. et al. 2023, PASP, 135, 1043
The Near Infrared Imager and Slitless Spectrograph for the James Webb Space Telescope. IV. Aperture Masking Interferometry