Algorithms for calwebb_coron3, which is stage 3 of the JWST Science Calibration Pipeline for coronagraphic data, are used to process data from calibrated slope images to combined, reference-PSF-subtracted coadded images.
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Unless otherwise stated, the algorithms described are the baseline version.
Steps for all coronagraphic data
Note that all steps in this module are common to both NIR and MIR data.
Assemble reference PSFs
Software documentation outside JDox: Stack Refs
The available list of reference PSFs is generated. These reference PSFs can include reference stars specifically observed for the target as well as observations of the target taken at different orientations.
Software documentation outside JDox: Outlier Detection
Outlier detection is done using the image stack. The majority of the outliers will be due to cosmic rays undetected during the 1st pass at outlier detection done in calwebb_detector1. An iterative sigma clipping algorithm is used in pixel coordinates on the image stack. The presence of an outlier results in a pixel flag being set.
Align reference PSFs
Software documentation outside JDox: Align Refs
The reference PSFs are aligned with the target observation using the Fourier LSQ algorithm to measure the shifts and the Fourier Shift algorithm to apply the shifts to each reference PSF integration.
Reference PSF subtraction
Software documentation outside JDox: KLIP Processing
The reference PSF that is subtracted from each target integration is created using the list of reference PSFs and the KLIP algorithm (Soummer et al. 2012).
Software documentation outside JDox: Resample
The target images (including those at different rotations) are resampled and combined into a single image where the distortion has been removed, and where the pixels in the output image all have the same spatial scale, which is equal to the input detector pixel scale by default.
Exposure level products
The exposure level products are re-created at this stage to provide the highest quality products that include the results of the ensemble processing (updated WCS, matching backgrounds, and 2nd pass outlier detection). These products are for the Archive and include the unrectified 2-D images and rectified 2-D images.
Soummer, R., Pueyo, R., Larkin, J., 2012, ApJ, 755, 28
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