JWST NIRSpec instrumentation components include optics, dispersers and filters, detectors, the micro-shutter assembly, an integral field unit, and fixed slits.
The JWST Near Infrared Spectrograph (NIRSpec) enables 0.6–5.3 μm spectroscopy at resolving powers of ~100, ~1,000, and ~2,700. NIRSpec offers 4 observing modes: (1) multi-object spectroscopy (MOS), (2) integral field unit (IFU) spectroscopy, (3) fixed slit (FS) spectroscopy, and (4) bright object time-series (BOTS) spectroscopy. The NIRSpec instrument hardware components used to carry out science in these modes are as follows:
- NIRSpec optics: NIRSpec is an all-reflective instrument with a total of 14 mirrors along the light path, and interchangeable filters and disperser options to cover the science wavelength range. The NIRSpec Optics article describes the basic optical path and components. NIRspec optics are shared for all three observing modes: multi-object spectroscopy mode, fixed slit mode, and IFU mode observing modes.
- NIRSpec dispersers and filters: NIRSpec is sensitive to nearly a full decade in wavelength: 0.6–5.3 µm. The NIRSpec optical path contains 2 wheel mechanisms—the filter wheel assembly (FWA) and the grating wheel assembly (GWA)—that provide disperser/filter combinations to cover the NIRSpec wavelength range. The NIRSpec Dispersers and Filters article describes the FWA and GWA components used for spectroscopy.
- NIRSpec detectors: NIRSpec uses 2 "long wavelength cutoff" Hawaii-2RG detectors manufactured by Teledyne Imaging Systems to acquire near-infrared spectra in the 0.6–5.3 μm spectral range. The NIRSpec detectors have 2048 × 2048 pixels; the inner 2040 × 2040 pixels are light sensitive.
- NIRSpec micro-shutter assembly: The NIRSpec micro-shutter assembly (MSA) is a configurable slit mask for multi-object spectroscopy, allowing the simultaneous collection of dozens to hundreds of target spectra within a 3.4' × 3.6′ FOV.
- NIRSpec integral field unit: this NIRSpec observing mode obtains the spectra of a contiguous, extended 3" × 3" area on the sky. To achieve this, the IFU uses specialized optics to "slice" the extended spatial region and reformat it into a slit alignment that can be dispersed using the NIRSpec spectrograph optics. The NIRSpec Integral Field Unit article describes some key characteristics of the NIRSpec IFU.
- NIRSpec fixed slits: the NIRSpec fixed slit spectroscopy mode can obtain the spectra of single sources at high sensitivity and contrast. To achieve this, the FS mode uses a selection of 5 slit apertures with the NIRSpec spectrograph optics shared with the MOS and IFUobserving modes. The NIRSpec Fixed Slits article describes some key characteristics of the NIRSpec FSs.
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