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Jupiter's Moon Io Caught Erupting in Keck Telescope Image
Jupiter's Moon Io Caught Erupting in Keck Telescope Image
12 Jan 2000
(Source: Keck Observatory)

W.M. Keck Observatory

MAUNA KEA, Hawaii - The successful installation and operation of a 21-st century adaptive-optics system at the W.M. Keck Observatory has ushered in a new era of ultra high-resolution astronomical imaging capability.

Recent observations with the Keck adaptive-optics (AO) system have produced the highest spatial-resolution images ever obtained from ground or space by an optical-infrared telescope. Funded by the W.M. Keck Foundation, the $7.4 million AO system was installed on the 10-meter Keck II telescope in February 1999. A clone of the instrument will be installed on the twin Keck I telescope this year.

While adaptive optics previously have been demonstrated on 4-meter class telescopes, the Keck AO system is the first to be installed on the new generation of 8-10 meter telescopes - thus taking advantage of the larger apertures' diffraction limit.

The Keck AO system senses and adjusts for distortions in starlight introduced by the Earth's atmosphere. The system splits off the optical portion of the light to sense the distortion while transmitting the corrected infrared light to the science instrument. Corrections are sent to a flexible mirror at up to 670 times per second.

The resultant images have an improved resolution more than tenfold - from about half an arc-second to tens of milli-arc seconds.

"The Keck AO system has opened up new astronomical frontiers by realizing the full angular resolution capability of a 10-meter telescope combined with its light-gathering power," said Keck optics manager Dr. Peter Wizinowich. "We can now observe objects at a level of detail 10 to 20 times higher than without an AO system."

Since AO first light, astronomers at Keck have used the system to image Neptune, Saturn's moon Titan, the asteroid Vesta, Jupiter's volcanic moon Io; explore binary-star systems previously beyond resolution, the heart of our Milky Way galaxy, and distant galaxies. The recent images of Io caught an apparent limb eruption and the surface albedo variations are clearly visible. A series of images of Vesta have been made into a movie that clearly shows the asteroid's rotation. (See images at:

The first phase of the Keck AO system currently uses natural guide stars to sense atmospheric distortion. An artificial guide-star system using a sodium-wavelength laser designed by a team from Lawrence Livermore National Lab will open the full sky to AO observations when it comes online in the next year. Currently less than 10 percent of the sky has a guide-star bright enough for AO correction.

The Keck AO system now uses an engineering-grade camera (K-Cam) with a 256x256 indium-antimonide detector for science imaging. The addition of the Near Infrared Spectrometer (NIRSPEC) and the next-generation Near Infrared Camera (NIRC 2) this year with their 1024 x 1024 InSb arrays and improved sensitivities will add powerful new tools to the Keck II repertoire.

The installation of the Keck I AO system later this year will be an important step toward combining the light of the two Keck telescopes to achieve even higher resolution.

"We are currently working with JPL (Jet Propulsion Laboratory) to build an interferometer that will have 10 times the angular resolution of an individual Keck telescope," said Wizinowich.

The Keck Adaptive Optics Team members included Scott Acton, John Gathright, Olivier Lai, William Lupton, Chris Shelton, Kevin Tsubota and Peter Wizinowich at Keck Observatory; and Jong An, Ken Avicola, Herb Friedman, Don Gavel, Erik Johansson, Bruce Macintosh, Scot Olivier and Claire Max at Lawrence Livermore National Laboratory.

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Last Updated: 5 Jun 2001