Description
- Class:
- Alias:
imprint
The NIRSpec MSA imprint subtraction step removes patterns created in NIRSpec MOS and IFU exposures by the MSA structure. This is accomplished by subtracting a dedicated exposure taken with all MSA shutters closed and the IFU entrance aperture blocked. These exposures are called “imprint” or “leakcal” images.
The imprint subtraction step has two input parameters: the target exposure and a
list of one or more imprint/leakcal exposures. When called as a standalone step, these
arguments can be provided as either file names or JWST data models. When the step is called
in the context of the calwebb_spec2 pipeline, imprint/leakcal file
names should be specified in the input spec2 association file, labeled with the member
type of “imprint”.
In the event that multiple imprint images are provided, the step uses the metadata of the target and imprint exposures to find the imprint exposure that matches the observation number (keyword “OBSERVTN”), dither pattern position number (keyword “PATT_NUM”), and background target flag (keyword “BKGDTARG”) of the input exposure. The matching imprint image is then subtracted from the target image. If no matching imprint image is found, the step will be skipped, returning the input target image unaltered.
When subtracting the imprint data model from the target data model, the SCI data array of the imprint exposure is subtracted from the SCI array of the target exposure, and the DQ arrays of the two exposures are combined using a bitwise logical OR operation. The error and variance arrays are not currently used or modified.
Step Arguments
The imprint subtraction step has no step-specific arguments.
Reference File
The imprint subtraction step does not use any reference files.