Description

Overview

The barshadow step calculates the correction to be applied to NIRSpec MSA data for uniform sources due to the bar that separates adjacent microshutters. This correction is applied to multislit data after the pathloss correction has been applied in the calspec2 pipeline.

Input details

The input data should be from after the extract_2d step, so that it contains cutouts around each slitlet.

Algorithm

The reference file contains the correction as a function of Y and wavelength for a single open shutter (the DATA1X1 extension), and for 2 adjacent open shutters (DATA1X3). This allows on-the-fly construction of a model for any combination of open and closed shutters. The shutter configuration of a slitlet is contained in the attribute shutter_state, which shows whether the shutters of the slitlet are open, closed or contain the source. Once the correction as a function of Y and wavelength is calculated, the WCS transformation from the detector to the slit frame is used to calculate Y and wavelength for each pixel in the cutout. The Y values are scaled from shutter heights to shutter spacings, and then the Y and wavelength values are interpolated into the model to determine the correction for each pixel.

Output product

The output product has the barshadow correction attached to each slit of the multislit datamodel in the BARSHADOW extension.