NIRISS

 The Near Infrared Imager and Slitless Spectrograph supports four observing modes: SOSS, AMI, WFSS and Imaging.

Observing
Mode
Use
Case
Pupil
Wheel
Filter
Wheel
Spectral
Range
Resolving
Power
Characteristics
SOSSTime Series Observations (Exoplanet Transit Spectroscopy)GR700XDCLEAR (Slitless)1st Order:
0.85-2.80 um
2nd Order:
0.60-1.40 um
1st Order: 650 @ 1.25 um
Saturation Limiting Magnitudes:
SUBSTRIP96: J>6.3
SUBSTRIP256: J>8.1
FULLFRAME: J>8.9
AMIHigh Angular Resolution ImagingNRM - 7 holesF277W, F380M,
F430M or F480M
--Contrasts <8-9 mag between 0.1'' and 0.4''
WFSSLow Resolving Power Slitless SpectroscopyGR150C or GR150RF090W, F115W, F140M, F150W, F158M or F200WSet by blocking filter (0.8-2.2 um)1st Order: 140 @ 1.3 umTwo grisms oriented at 90 degrees to mitigate contamination
ImagingCurrently only supported as part of the WFSS direct image observations.F090W, F115W, F140M, F150W, F158M, F200W
or CLEARP
F277W, F356W, F380M, F430M, F444W, F480M or CLEAR--FOV: 2.2' x 2.2'
Pixel Scale: 65 mas

The SOSS mode was designed to enable 0.6-2.8 microns low resolving power (R=700) exoplanet transit spectroscopy. The slit-less spectrograph uses a cross-dispersed grism in first and second orders, a weak cylindrical lens to defocus the trace to 23 pixels in the spatial direction and detector subarrays to target bright objects (6.3<J<12).

ModesTraces_inverted

The WFSS mode was designed to obtain low-resolving power (R=150) slit-less spectra of a large amount of targets simultaneously within the 2.2’x2.2′ field of view of NIRISS. There is a choice between two grisms producing spectra at orthogonal angles to each other to mitigate contamination in crowded fields. Blocking filters determine the wavelength coverage (0.8-2.2 microns).

CLASH_gr150horizCLASH_gr150verti

AMI is a high angular resolution imaging mode making use of a non-redundant mask (7 holes in the pupil) to produce interferograms. This mode allows to peer to inner working angles smaller (0.1″ – 0.4″) than other types of imaging with JWST, albeit at shallower contrasts of 8-9 magnitudes near 4 microns.

NRM_maskbinaire