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James Webb Space Telescope
NIRISS at a Glance

Layout of NIRISS
Schematic of NIRISS

Detector Characteristics

Array size2048 x 2048 pixel HgCdTe array
Pixel size18 µm x 18 µm
Dark rate< 0.02 e-/s
Noise23 e- (correlated double sample)
Gain1.5 e-/ADU
Field of View (FOV)2.2' x 2.2'
Plate scale in x0.0654 arcsec/pixel
Plate scale in y0.0658 arcsec/pixel

Observation Modes

Optical elements in the Pupil and Filter Wheel of NIRISS support 4 modes of observation:

  • Wide-Field Slitless Spectroscopy (WFSS), R~150; 1.0 – 2.5 microns; enabled by a matched pair of orthogonal grisms (GR150C and GR150R) in the Filter Wheel and a selection of blocking filters in the Pupil Wheel (F115W, F140M, F150W, F158M, F200W).
  • Single-Object Slitless Spectroscopy (SOSS), R~700; 0.6 – 2.5 microns; enabled by the grism GR700XD, which generates 3 orders of cross-dispersed (XD) spectra for a target placed at a reference point in the FOV.
  • Aperture Masking Interferometry (AMI), 3.8 – 4.8 microns; enabled by the non-redundant mask (NRM) in the Pupil Wheel and medium-band filters (F380M, F430M, F480M) in the Filter Wheel. The mask consists of 7 "holes" (apertures), which produce an interferogram that samples 21 unique ("non-redundant") baselines.
  • Imaging, 0.9 – 5.0 microns; enabled by wide-band filters F090W, F115W, F150W, F200W in the Pupil Wheel and F277W, F356W, F444W in the Filter Wheel.