NIRCam WFSS and Grism Calibration Status

The overall calibration status and estimated accuracy of NIRCam wide field slitless spectroscopy (WFSS) and grism time-series observations are described in this article; please also see the article on known issues affecting NIRCam data.

On this page

Note that all wavelength information is given in the barycentric vacuum rest frame.

Photometric calibration


The absolute flux calibration uncertainties for the grisms are about 2% (all filters/detectors). The grism subarrays and full frame observations agree to within about 2% based on images in those subarrays using standard stars.

Wavelength calibration


Generally ~0.25 pixels, or 2.5 Å, over the whole field of view using the latest calibration data. The wavelength is tied to NIRSpec long slit observations of a planetary nebulae. 

Spectral trace accuracy


All positions, offsets, traces, and spectral shapes of the 1st orders are calibrated to within ~0.25 pixel over the entire field of view. That is, given a coordinate x0, y0 for a source, it can be predicted where the spectral trace will fall on the detector in the WFSS observation down to 0.25 pixel on the detector in WFSS mode. The modeling/calibration of this includes field dependence and variation of the shape of the spectral traces as a function of position. 

Target acquisition performance


For grism time series, TA uncertainty has been measured to be ±0.3 px (0.02") for the F335M and ±0.15 (~0.01") for the F405N filters, respectively.

Notable updates

Originally published