About the Subaru Telescope

Observational instruments

Infrared Camera and Spectrograph (IRCS)

Infrared Camera and Spectrograph (IRCS)


IRCS is a versatile near-infrared camera and spectrograph, which can capture either images or spectra in the wavelength range of 1-5 microns. In its camera mode, it can image efficiently throughout the 1-5 micron range, especially at longer wavelengths. When used in its spectroscopy mode, it provides relatively high spectral resolution that can disperse light for fine to broad measurements of the motion or chemical composition of objects. It was designed to perform best when used with the adaptive optics system. Its versatility is particularly suited for the study of a variety of celestial objects such as star-forming regions, brown dwarfs, galaxies, and far-distant targets.

Fast Facts


  • Near-infrared camera and spectrograph
  • Optimized for high-resolution images with adaptive optics


  • Versatile near-infrared camera with powerful observing capability
  • Functions in several modes
  • Infrared imaging
  • Low to intermediate dispersion spectroscopy with grism
  • High dispersion spectroscopy with echelle grating
  • Use of the same camera for imaging and spectroscopy without having to be moved
  • Can switch between spectroscopic and imaging modes very quickly.
  • Allows for observational flexibility by taking full advantage of the weather, seeing conditions, or time-critical events.
  • Capable of wide range of spectral resolution observations
  • Low and high dispersion over the entire 1-5 micron spectral range
  • From low (100) resolving power (R) to a high of 20,000


  • Size and weight:
  • Placement: infrared Nasmyth focus (originally at Cassegrain focus)
  • Wavelengths: near infrared, 1-5 microns
  • Detectors
  • Camera: ALADDIN III 1024 x 1024 InSb array
  • Spectrograph: ALADDIN III 1024 x 1024 InSb array
  • FOV/slit dimensions
  • Camera: two plate scales
  • High
  • 20 milliarcseconds (mas) per pixel for use with AO
  • FOV of 21 arcseconds
  • Low
  • 52 mas (general purpose, without AO)
  • FOV of 54 arcseconds
  • Spectrograph
  • Slit width of 0.15 arcsecond and above
  • Cross-dispersed spectrograph providing mid to high spectral resolution. Resolving power (R) ranges from 5,000-20,000.
  • Uses grisms or grating prisms for lower spectral resolution observations.
  • Uses echelle grating to disperse light into greater detail for high spectral resolution observations.
  • Filters for imaging
  • A range of narrow- and broad-band filters
  • Three filter wheels


  • Investigate chemical reactions around stars.
  • Detect small differences in relative motions that relate to studies of gases within objects ranging from young stars to entire galaxies.
  • Search for brown dwarfs or "failed stars".
  • Study the dynamics of distant galaxies.


  • Developers
  • Collaboration between the Institute for Astronomy (IfA), the University of Hawaii, and the National Astronomical Observatory of Japan (NAOJ), with funding from NAOJ
  • All of the development work, design, and fabrication were done a IfA in Honolulu.
  • Some major components were designed, assembled, and cryogenically tested at outside companies and delivered to IfA.
  • Manufacture of all lenses by Optics for Research, Inc.
  • Broadband filters made by near-infrared filter consortium organized by A. Tokunaga and D. Simons and manufactured by Orbit.
  • Echelle and cross-disperser gratings manufactured by Hyperfine Inc.
  • 2005 upgrade to Nasmyth infrared with AO 188 by Subaru Telescope
  • 2013 addition of NH3 gas cell
  • For use in part of K-band with AO188 mode only
  • Provided by A. Seifahrt (U. of Chicago) in collaboration with colleagues at the U. of Goettingen (Germany) and Lund Observatory (Sweden).

Specialized Information about the Instrument and Observing: