NIRISS Observing Modes

JWST's Near Infrared Imager and Slitless Spectrograph (NIRISS) has observing modes for imaging, low-resolution wide field grism spectroscopy, single object grism spectroscopy, and high spatial resolution imaging using aperture masking interferometry.

The JWST Near Infrared Imager and Slitless Spectrograph (NIRISS) has four observing modes with unique capabilities for imaging and spectroscopy that correspond to templates in the Astronomer's Proposal Tool (APT):

  • Wide field slitless spectroscopy (0.8–2.2μm) over a 2.2' × 2.2' field of view using two identical orthogonal grisms with R = λ/Δλ = 150;
  • Single object slitless spectroscopy (0.6–2.8μm) for bright targets in two cross-dispersed orders using the R = λ/Δλ = 700 grism, optimized for time-series observations (TSOs);
  • Aperture masking interferometry which offers the highest spatial resolution imaging on the JWST, using a non-redundant mask (NRM), reaching a contrast of 10-4  for separations of 70–400 mas;
  • Imaging (0.8–5.0μm) over a 2.2' × 2.2' field of view with pixel scale ≈ 0.065"/pixel.


Table 1. Specific properties of NIRISS observing modes

Observing
mode

Wavelength
coverage (μm)

Field of
view
(arcsec)

Pixel scale
(arcsec/
pixel)

Resolving power
R = λ⁄Δλ

FWHMComment

Wide field
slitless spectroscopy 
(WFSS)
 

0.8–2.2133 × 1330.065150 @ 1.4 μm
...

Orthogonal dispersion
orientations available

Single object
slitless
spectroscopy
(SOSS)

0.6–2.8

...0.065700 @ 1.4 μm...Subarrays are standard;
full-frame allowed
Aperture masking
interferometry 
(AMI)

2.8–4.8

5.2 × 5.20.065......Subarray is standard;
full-frame allowed
Imaging0.8–5.0133 × 1330.0654–102 pix @3.4  μmFull-frame standard;
only used in parallel mode




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