Observational Instruments

The Subaru Telescope was designed for long-term versatility as a major tool in observational astronomy, which focuses on the use of instruments mounted on the telescope to observe celestial objects. The sensors or detectors of the instruments capture light collected by the primary mirror and then convert it into a form that researchers can use as data in their computers. The instruments play a crucial role in the scientific process of feedback between observation, analysis and discovery, all of which contribute to an accurate, deep understanding of the Universe.

The relatively large numbers of instruments for the Subaru Telescope were carefully chosen and designed to allow for exploration of as wide a range of astronomical phenomena as possible, e.g., exoplanets, far-distant galaxies, dark energy, dark matter. The nine cameras and spectrographs span optical and infrared wavelengths, which represent light at different points along the electromagnetic spectrum. Optical light is that part of the spectrum that is visible to and detectable by the human eye, while infrared light is not.

The instruments perform different functions with the light they receive; the detectors in each of the instruments are sensitive to either the optical or the infrared range but not both. Cameras capture images of objects that show their structure and brightness. Spectrographs spread the objects' light into their constituent colors to indicate such features as their temperature, chemical composition, and motion. Infrared instruments have sensors equipped to penetrate dusty regions of space, e.g., star-forming regions, and detect objects such as planets or those that existed in the early days of the universe. Instruments may operate solely as cameras or spectrographs or both. The table below shows the diversity and range of Subaru Telescope's instruments.

Optical Infrared
Camera HSC
Camera and Spectrograph FOCAS MOIRCS
Spectrograph HDS

The detection, analysis, and discovery of objects ultimately depend upon the amount of light collected by the primary mirror. Since the Subaru Telescope has one of the largest primary mirrors (8.2 m) in the world, researchers benefit from the combination of its light-collecting power and the versatility of its large suite of instruments.

Astronomers can customize their observations and choice of instruments to align with their particular scientific priorities. The descriptions that follow outline the main features and applications of each of the current suite of instruments and highlight their special roles in observations. Also included is a description of the adaptive optics system, which minimizes the distortion of light produced by atmospheric turbulence and enables finer resolution for near-infrared observations.

For Scientists

Current Subaru Instruments

Hyper Suprime-Cam (HSC)

Hyper Suprime-Cam (HSC) mounted on the prime focus of the Subaru Telescope started to serve as a facility instrument for open use from 2014. It offers a ultra wide field view equivalent of the 9 of the size of the full Moon. Total pixel number is more than 87 million with 116 of highly sensitive CCDs. Researchers started to take advantage of the wide field capability of this camera for surveying variety of objects such as the distant galaxies to reveal the dark matter distribution.

Topics: Image of M31 Heralds the Dawn of HSC's Productivity (July 30, 2013)


Multi-Object Infrared Camera and Spectrograph (MOIRCS)

MOIRCS is a near-infrared camera and spectrograph that combines a wide field of view with the capacity to capture the spectra of about 40 objects simultaneously. Its most notable feature is its multi-object spectroscopy, which opens a large window to the Universe by allowing researchers to obtain infrared spectra for a large number of objects in a single observation.


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.


Cooled Mid Infrared Camera and Spectrometer (COMICS)

COMICS is a mid-infrared camera and spectrograph, which can detect warm dust that emits strong radiation in space and that cannot be seen in optical wavelengths. The thin, dry air of Subaru Telescope's location at Mauna Kea's summit permits easier detection of mid-infrared light, which is usually absorbed before it can reach the ground. One of COMICS's main scientific purposes is to study the structure and evolution of planet-forming disks to reveal how planetary systems form. It is particularly suitable for observing dusty star-forming regions, comets, and accretion disks around protostars.


Faint Object Camera And Spectrograph (FOCAS)

Designed for high-sensitivity optical observations of faint celestial objects, this versatile instrument includes all of the fundamental modes of optical astronomy: imaging, spectroscopy, and polarimetry. Its multi-object spectrograph, which enables observations of the spectra of about 50 objects at once, allows astronomers to determine the distance and detailed physical properties (e.g., chemical composition, mass, stellar population) of very faint celestial objects in far-distant galaxies. The data it produces contribute to an understanding of the origin and evolution of the Universe.


High Dispersion Spectrograph (HDS)

The High Dispersion Spectrograph provides extremely high spectral resolution observations in visible light. Capable of dividing light into as many as 100,000 different colors and observing them simultaneously, it is notable for its high resolving power in spectroscopy. HDS plays an active role in measuring spectra to indicate the presence of exoplanets as well as to evaluate the abundance of elements in very old stars formed at the beginning of the Universe.


188-Element Adaptive Optics (AO)

Subaru's 188-element AO system includes laser guide star technology, which allows observers to use a laser as an artificial star when there is no bright guide star illuminating an object-star. The development of the 188-element system was a product of continual improvements to Subaru's earlier 36-element AO system, which was designed, produced, and then made available to astronomers worldwide in 1990. The current 188-element AO system successfully passed its first test on October 9, 2006 and replaces the older system. This 188-element AO mounts at the infrared Nasmyth focus.

Wavelength Regime

Larger Image (69KB)

Each of Subaru's seven instruments detects light of either the optical or the infrared. Instruments like FOCAS and IRCS function as both a camera and a spectrograph. HDS specializes in high resolution spectroscopy. The figure on the left shows the wavelength regime detected by the instruments above and how finely each can divide that light into component of wave-lengths or colors (spectral resolution). Instruments with different fields of view or special features optimized for particular scientific targets sometimes have overlapping wavelength and resolution coverage.

Former Generation Instruments


Subaru Prime Focus Camera (Suprime-Cam)

Suprime-Cam is an 80 megapixel, optical camera mounted at the Subaru Telescope's prime focus. Among large telescopes (6-10 m), it has the extaordinary capability not only of efficiently imaging a wide field of view but also of capturing images of very faint objects with high levels of detail and contrast—in a single exposure. It is an ideal tool to: 1) survey large areas of the distant Universe, particularly for studying the birth and evolution of galaxies, 2) detect small bodies on the outskirts of the Solar System, especially the Edgeworth-Kuiper Belt, and 3) map the distribution of dark matter in the Universe.


Fiber Multi-Object Spectrograph (FMOS)

FMOS is a powerful, fiber-fed, wide-field spectroscopy system that enables near-infrared spectroscopy of over 100 objects at a time. It is composed of three subsystems: 1) an infrared unit at prime focus (PIR) that includes a wide-field corrector lens system and fiber positioning system ("Echidna"), 2) a fiber bundle unit of 400 optical fibers, and 3) two spectrographs. Echidna can precisely position all 400 fibers in just 15 minutes. This high speed for repositioning allows observers to reconfigure Echidna, observe multiple fields during a night and rapidly observe hundreds of faint targets that can be compiled as data for statistical analysis.

Coronagraphic Imager with Adaptive Optics (CIAO)

CIAO is an infrared imager, designed to detect fainter objects near bright ones by blocking out the light of the brighter ones. It can image the immediate neighborhood of stars where planets may be forming and study stars that are ejecting gas and dust into interstellar space as they die.


Topics (April 2000) CIAO First Light !

36-Element Adaptive Optics (AO)

The Subaru telescope has achieved an angular resolution of 0.2 arcsec at wavelength of 2 μm by minimizing air turbulence inside the enclosure. This resolution is, however, still limited by atmospheric turbulence. With the Adaptive Optics system, which can compensate for the distorted wavefront very rapidly, the light can be focused still further, limited only by the diameter of the primary mirror. For many observations, this limit of 0.06 arcsec exceeds the resolution of the Hubble Space Telescope. The 36-Element AO is mounted at the Cassegrain Focus of the Subaru Telescope.


Scientific Results (December 2000) Adaptive Optics First Light !

OH-Airglow Suppressor (OHS)

By eliminating infrared light emitted by OH airglow in the upper atmosphere, OHS achieves the high sensitivity required to obtain spectra of faint objects such as distant galaxies and brown dwarfs. It sits at the IR Nasmyth focus. This picture shows CISCO, the imaging camera for OHS, which has been working excellently since First Light.


Topics (May 2000) OHS First Light !

Guidelines for use

document navigation