Jul 13 2007
A new sodium laser is giving 50 times more sky coverage to the atmospheric-correcting technology known as adaptive optics on the Keck II telescope at Mauna Kea, Hawaii.
The laser lets scientists explore most of the sky with adaptive optics and gives them the capability to study objects that were previously too faint to be seen with the system. Since 1999, Keck Adaptive Optics has provided 10 times more resolving power than what could otherwise be achieved from the ground. The results are producing infrared images from the ground comparable – and often better – than those taken from space.
“This has been the most exciting technological and scientific breakthrough for the Observatory in the last decade. It may forever change the way we do astronomy from the ground,” said W. M. Keck Observatory Director Fred Chaffee. “We are entering a new, extraordinary era of discovery.”
After just one year of regular scientific use, the Keck Laser Guide Star Adaptive Optics system is producing spectacular results and advancing research in several fields of astronomical study. Findings include the discovery of new asteroids, moons and planetoids in our solar system, the detection of new brown dwarf binary systems -- including a strange new kind of binary, observations of physical processes taking place near a supermassive black hole, and new findings about extremely distant supernovae and young galaxies.
The technique of adaptive optics uses visible light from a bright star to measure and correct for atmospheric distortions at infrared wavelengths. But only about two percent of the sky has stars bright enough to use with adaptive optics. The Keck Laser Guide Star system overcomes this limitation by creating an artificial star anywhere in the sky. The W. M. Keck Observatory is the only 8 10 meter class facility in the world currently providing this capability to observers.
“The wish list for astronomers is pretty simple,” said Dr. David Le Mignant, adaptive optics scientist at the W. M. Keck Observatory. “First, they want the highest-quality images that can possibly be obtained. Second, they want to look anywhere they want to in the sky. The laser guide star makes both these wishes come true.”
Operating at nearly 1,000 times a second, the Keck adaptive optics system minimizes the blurring effects of Earth's atmosphere to provide infrared images 10 times better than what can be achieved from the ground. Without any correcting technology, the best telescopes on Earth are limited to an average “seeing” ability, or resolving power, of about 0.5 arcseconds, the equivalent of being able to distinguish an object the size of a blueberry from 2.5 miles (4 km) away. But with adaptive optics, atmospheric blurring is removed, producing a resolving power of about 50 milliarcseconds or better. This improvement is like looking at a penny from 2.5 miles away and being able to read the words, “ONE CENT” and “Liberty” stamped on the coin.
“We are shattering a limitation for ground-based observations -- astronomers can now uncover and study fine structures in extremely faint objects anywhere, within and beyond our galaxy, ” said Dr. Le Mignant. “This new data will particularly complement present deep sky surveys which study the formation of galaxies in the universe.”
More than 21 scientific results made possible with the Keck Laser Guide Star system are presented today at the 207th meeting of the AAS in Washington D.C. Among the many new significant findings discussed at Special Session 98, “Seeing the Universe in a New (Sodium) Light”:
* In the distant regions of our solar system, scientists at Caltech have used the Keck Laser Guide Star to discover three new satellites orbiting some of the largest objects in the Kuiper belt. The surprising properties of these moons suggest that they are formed very differently from the tiny moons known to orbit smaller Kuiper Belt Objects. (Antonin Bouchez, Caltech)
* At the center of our own Milky Way galaxy, the hostile environment around the supermassive black hole should make it difficult for stars to form, but a group of massive young stars has been detected and their origins are puzzling scientists. The problem has been dubbed “the paradox of youth.” Now, UCLA scientists are able to measure how these young stars move across the sky with an unparalleled precision of only two kilometers per second, and determine, for the first time, the orbit of each of the young stars located more than a few light months from the black hole. Scientists are using the stars' orbits, which retain an imprint of their origin, to understand how and where these young stars may have formed. (Jessica Lu, UCLA)
* Also in the Milky Way, scientists at the University of Hawaii are discovering new ultracool brown dwarf binary systems, including a strange new kind of binary never seen before. (Michael Liu, UH-IfA)
Scientists at UCSC and the Supernova Cosmology Project observed a supernova in a galaxy as it appeared when the universe was only 40 percent its current age (z=1.3). The Keck Laser Guide Star system allowed the team to study the faint system and resolve the supernovae from the galaxy core, separated by only 0.4 arcseconds. The discovery was made as part of a major, long-term project called “Center for Adaptive Optics Treasury Survey” or CATS, a project that is looking at deep Hubble galaxy fields with the Keck Laser Guide Star System. (Jason Melbourne, UCO Lick/UCSC)
“Major advances in astronomy are often the driven by having new technologies to explore the heavens,” said Michael Liu of the Institute for Astronomy at the University of Hawaii. “Through years of effort and dedication of many people, the Keck system is allowing us to see the whole of the universe in a new (sodium) light.”
More than 20 percent of all available observing nights through July 2006 on the Keck II telescope will use the sodium laser. Laser guide star systems do not outperform natural guide stars, but rather take over in the faint skies where sufficiently bright stars do not exist. With bright objects of magnitude 10 or greater, natural guide star systems still provide slightly better images, and will be used for about 30 percent of the adaptive optics research at W. M. Keck Observatory.
The Future
Regularly using sodium lasers with adaptive optics is in its early stages, but laser guide stars are being developed for most major observatories, most notably the European Southern Observatory's Very Large Telescope, the Gemini North and Gemini South telescopes and the National Astronomical Observatory of Japan's Subaru Telescope. Plans are also underway to install a new laser guide star system on the Keck I telescope within the next three years, and also to improve the efficiency and reliability of the existing laser system on Keck II.
Acknowledgements
The W. M. Keck Foundation provided major funding for the construction of the twin 10-meter Keck telescopes and for the adaptive optics and laser guide star systems. Additional funding for the Laser Guide Star Adaptive Optics system was provided by NASA, Lawrence Livermore National Laboratory (LLNL) and the Center for Adaptive Optics. The Laser Guide Star Adaptive Optics system was implemented by a team at W. M. Keck Observatory. The sodium laser was developed at LLNL. The W. M. Keck Observatory is managed by the California Association for Research in Astronomy, a non-profit 501 (c) (3) corporation whose board of directors includes representatives from Caltech, the University of California and NASA.
http://www.keckobservatory.org