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James Webb Space Telescope
NIRISS Performance/Sensitivity

Wide-Field Slitless Spectroscopy

The predicted sensitivity of the GR150C/R grism used in first order for observations of unresolved emission lines in spectra of point sources. The curves show the minimum line flux for a S/N of 10 in 10000 seconds, in MKS units (left y axis) or CGS units (right y axis). Each curve is for a different blocking filter. The extraction box has dimensions of 5 pixels and 3 pixels in the spatial and spectral directions, respectively. An adjacent region of the same size is used for the background measurement. At wavelengths below 0.845 microns the second order sensitivity is predicted to be better than the first order sensitivity, but those values are not shown in the plot. The 3-pixel binning in the dispersion direction is includes >90% of the emission from a point source at any given wavelength.

The predicted sensitivity of the GR150C/R grism used in first order for observations of continua in spectra of point sources. Sensitivity is defined as the minimum brightness for S/N of 10 in 10000 seconds. Values are given in MKS units (left y axis) and CGS units (right y axis). As in the unresolved line case, the sensitivity is better in second order at the shortest wavelengths but those values are not shown.

See the comparison of low-resolution spectroscopic performance of NIRISS with other JWST instruments.

Single-Object Slitless Spectroscopy

The predicted S/N obtained with the GR700XD grism in 1000 s for observations of the spectrum of Vega, scaled to K=7.0. Only the Poisson noise in the signal of the target is considered in these estimates.

The predicted S/N obtained with the GR700XD grism in 1000 s for observations of the spectrum of Vega, scaled to K=7.0. In these estimates, the noise is due to background sources only.

The predicted sensitivity of the GR700XD grism as a function of wavelength in first and second order. The extraction box has dimensions of 20 pixels and 3 pixels in the spatial and spectral directions, respectively. The background is estimated from a box of the same size adjacent to the spectrum.

Aperture Mask Interferometry

Angular Resolution with the NRM: NIRISS is capable of resolving objects at 0.2" with a contrast of 9.5 magnitudes and aims to achieve the same resolution for point sources with a contrast ratio of 12.0 – 12.4 magnitudes (source:- Lafrenière, D. and the JWST Aperture Masking (JAM) team)

Imaging

NIRISS Imaging Sensitivity Table