The Near-Infrared Spectrograph (NIRSpec) is one of Webb’s four scientific instruments. NIRSpec is one of Webb’s versatile tools for near-infrared spectroscopy. In addition to standard single-slit spectroscopy to gather spectra of specific objects, NIRSpec also has an integral field unit to investigate spatial variations in spectra and a microshutter array to capture individual spectra of dozens of objects at once. This highly efficient design is part of what makes Webb ideal for studying extremely distant, faint galaxies. NIRSpec was built for the European Space Agency by Airbus Industries with the microshutter array (MSA) and detector sub-systems fabricated by NASA.
NIRSpec Components Spectrographs spread light out into a spectrum so that the brightness of each individual wavelength can be measured. Webb’s microshutter array (MSA) is a grid of 248,000 tiny doors that can be opened and closed to transmit or block light in order to capture spectra of 100 individual objects or points in space at the same time. An integral field unit (IFU) is a combination of camera and spectrograph used to capture and map spectra across a field of view in order to understand variation over space.
NIRSpec Wavelength Range NIRSpec is designed to capture light ranging in wavelength from 0.6 microns (visible red) to 5 microns (mid-infrared).
NIRSpec Field of View An instrument’s field of view is the amount of sky that it can observe at any given point in time. (The actual area that can be observed depends on the distance of the object being observed.) In this graphic, a Hubble Space Telescope image of the Whirlpool Galaxy (M51) is shown for scale. The image covers an area of 9.6 × 6.6 arcminutes. (The full Moon has a diameter of about 31 arcminutes across the sky.) NIRSpec’s field of view covers a total area of roughly 3 × 3 arcminutes.
NIRSpec Imaging Modes None, with the exception of images collected during Integral Field Unit Spectroscopy.
NIRSpec Spectroscopy Modes Slitted Spectroscopy provides the ability to capture the spectrum of a single object—a single star, a single exoplanet, or a single distant galaxy—in a wide field of view. Multi-Object Spectroscopy involves using a microshutter array to capture individual spectra of up to 100 objects or locations in space at one time. Multi-object spectroscopy is important for efficiency, in particular when observing very distant and dim targets, such as ancient galaxies, which require hundreds of hours of observation time. Integral Field Unit Spectroscopy (IFU) involves a combination of imaging and spectroscopy. During an IFU observation, the instrument captures an image of the field of view along with individual spectra of each pixel in the field of view. IFU observations allow astronomers to investigate how properties—such as composition, temperature, and motion—vary between different objects such as stars in a crowded star field, or from place to place over a large region of space such as a galaxy or nebula. Time-Series Spectroscopy involves capturing the spectrum of an object or region of space at regular intervals in order to observe how the spectrum changes over time. Time-series spectroscopy is used to study planets as they transit their stars.
Credits
Illustration
NASA, ESA, Andi James (STScI)
