(Coronagraphic Imager with Adaptive Optics)

Hide a Star, Find a Planet

CIAO is designed to detect faint objects near a bright object by masking out the light from the brighter one. It can image the immediate neighborhood of stars where planets may be forming and where stars are ejecting gas and dust into interstellar space as they die.

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Light from a central bright star is removed by a circular mask, and then its diffracted and scattered light is also removed by a Lyot Stop. Thanks to this mechanism, a very faint object in the close vicinity of the central bright star becomes detectable.

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An image of Uranus, its ring, and two of its satellites Miranda (upper right) and Ariel (lower left) taken by CIAO with adaptive optics (AO). Methane, the main constituent of Uranus’ atmosphere, appears blue in this image. The apparent spatial extent of Uranus is only 3.6 arcseconds. The ring is clearly resolved.

A Near-Infrared View of Uranus, Its Ring system, and Two Satellites (Feb. 21, 2002)


GG Tau

GG Tau is a binary protostar. The companion star has covered an ring-like space out of the proto-planetary disk around the main star. The main star is a mid-sized star like our Sun. Astronomers hypothesize that around young star dust and gas from a disk, which later evolves into a planetary system. Such proto-planetary disks should be common, but so far few have been found.

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Death of a star seen in the near-infrared

A CIAO image of the planetary nebula BD+303639. At the end of their life, stars expel gas into interstellar space, and their central hot cores become visible. The expelled gas shines from the illumination by the cores. This expelled gas will gather together into clumps of gas, from which new stars will form.

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CIAO is a specialized instrument equipped with a coronagraph. The first coronagraphs were made for observing the Sun’s corona by blocking the light from the Sun’s photosphere. CIAO is designed to block light from a star so that we can study proto-planetary disks and other faint objects in the neighborhood of something bright. The development of CIAO was a challenging for Japanese astronomers because CIAO combines stellar coronagraphy, adaptive optics, and an 8-meter class telescope, all firsts for Japanese astronomers.

The objects that we would like to study using CIAO are usually more than 1,000 to 10,000 times fainter then the central star. Unless weather conditions are superb, even with Subaru’s large aperture and AO system, it is extremely difficult to remove the light from the star that is dispersed by the Earth’s atmosphere. We can expect CIAO’s best results to come once Subaru implements a queue observing system. Under a queue observing system, abserving instruments are selected on the basis of weather, and CIAO can be on the telescope only when atmospheric conditions are good enough for coronagraphic observations.

In October 2002, Subaru began a survey of the environment of young stars as an observatory project. The survey is designed to test theories on how the environment around a young star evolves. We hope to have exciting results in the next two to three years.

(From a late 2002 interview with Koji Murakawa, CIAO support astronomer.)




We plan to upgrade the current AO system as we continue to observe with it. The two major upgrades are: increasing the number of actuators for the deformable mirror and introducing a laser guide star system. By increasing the number of actuators, we can correct smaller distortions in the wave front. The new AO system will be more effective under bad seeing conditions and at shorter wavelengths. A laser guide star system will increase the number of observable objects. The AO system requires a bright guide star near the target object for measuring disturbances in the wave front. A laser guide star system makes an artificial guide star when a natural guide star is missing by generating a light spot on the sodium layer of the Earth’s atmosphere at an altitude of 90 kilometers. Using a laser star system, the bulk of the sky accessible from Mauna Kea becomes observable with AO.






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