The operational aspects of JWST's NIRSpec instrument define how instrument-level capabilities can be applied for science. These features include target acquisition methods, dither/nods for each observing mode, and special considerations for science observations.
The JWST Near Infrared Spectrograph (NIRSpec) enables 0.6–5.3 μm spectroscopy at resolving powers of ~100, ~1,000, and ~2,700 in multi-object spectroscopy (MOS), integral field unit (IFU) spectroscopy, fixed slit (FS) spectroscopy, and bright object time-series (BOTS) spectroscopy modes.
These NIRSpec science modes include the following operational capabilities:
- NIRSpec target acquisition
NIRSpec dithering strategies
Dithering of spectroscopic observations is necessary to improve coverage of the sky, cover gaps between detectors, correct for detector defects and pixel-to-pixel response fluctuations, and to improve the sampling of the point- and line-spread functions of the instrument. MOS, IFU, and FS modes have dithering strategies to accomplish these goals in the articles listed below:
- NIRSpec MOS operations
- NIRSpec IFU operations
- NIRSpec FS operations
NIRSpec auto-cals (auto-calibrations) are internal calibration exposures that can be acquired with lamps within the NIRSpec calibration assembly (CAA). These auto-cals can be acquired for flat fields, wavelength reference exposures, and broad line peaks measured for dispersion verification.
It is not recommended for users to acquire NIRSpec auto-cals with their science for two reasons:
- Acquiring auto-cals can cause moderate overheads, ~5 minutes or more per exposure.
- Acquiring auto-cals with lamp illumination may cause low levels persistence in subsequent science that could effect very deep sky exposures on faint objects.
NIRSpec auto-cals have been added to the science templates for FS, IFU, and MOS observing modes to make it possible to acquire lamp exposures at the same time as on-sky external exposures. It is expected this capability will primarily be used for instrument commissioning and observatory calibration observations.