Spectroscopic Modes Spectrum Image
Available for NIRSpec
Available for NIRSpec and MIRI
Available for NIRSpec, MIRI, NIRISS and NIRCam
NIRSpec provides observations through fixed slits of 0.2 x 3.3, 0.4 x 3.8, and 1.6 x 1.6 arcsec with all three spectral resolutions (R~100,1000 and 2700). These permanently-open slit apertures are intended primarily for high-dynamic-range observations of a single target (e.g., exo-planet transits).
The NIRISS Single-Object Slitless Spectroscopy (SOSS) mode is specifically optimized for bright-target spectroscopy. The optical design defocuses the light from the bright targets and disperses it into three orders, allowing observations without saturating the detector. This mode provides a spectral resolution of R=750 from 0.6 to 2.5 μm.
The MIRI low-resolution spectrometer (LRS) provides R ~ 100 long-slit and slitless spectroscopy from 5 to 12 μm and is optimized for observations of compact sources. The slit mode provides a 5.5" long and 0.6" wide entrance aperture, while the slitless mode provides very accurate spectrophotometry for Time Series Observations, such as transiting exoplanets. The prism disperses the 5 to 10 micron spectral band of light from the target over approximately 140 detector pixels.
NIRCam has a grism with a spectral resolution R~2000 in the 2.4-5 micron channel. Its primary purpose is to assist with the coarse phasing of JWST. But the grism can also be used for scientific observations, including slitless spectroscopy of bright targets.