'Razor-sharp image' of star cluster snapped from Earth
GEMINI OBSERVATORY NEWS RELEASE
Posted: June 2, 2003
Among several of the first images from Altair (Altitude Conjugate Adaptive Optics for Infrared), the high- resolution data reveal multitudes of stars with stunning clarity. The dense star cluster known to generations of skywatchers as the Great Hercules Cluster or M-13 is home to hundreds of thousands of stars that, in the center, are often blurred by our atmosphere into a great glowing mass. "The resolution obtained in these images is approximately equivalent to seeing the separation between an automobile's headlights on the Golden Gate Bridge in San Francisco while standing 3,850 kilometers away in Hawaii," said Observatory Adaptive Optics Scientist Dr. Francois Rigaut.
The remarkable detail in the Gemini images was made possible by Altair's unique ability to correct starlight that has been blurred by atmospheric turbulence using adaptive optics with altitude conjugation.
Most adaptive optics systems that are currently in use correct for distortions to starlight by assuming that all of the distortions occur where starlight is collected -- near the surface of the telescope's primary mirror. In an altitude- conjugated system like Gemini's, the distortions are assumed to be at the dominant turbulence layer of the atmosphere. By conjugating or tuning the system for a specific layer above the telescope, Altair can generate a more accurate model of the starlight's path through our atmosphere.
"Adaptive optics with altitude conjugation is a pioneering new technique that is a powerful way to measure and fix distortions to starlight, which traveled undisturbed for vast distances through space until hitting pockets of warm and cold air in Earth's atmosphere," said Glen Herriot, the systems engineer who managed the building of Altair in Victoria, BC at the laboratories of the National Research Council of Canada. Altair is able to precisely correct the distorted starlight up to 1,000 times per second using a sophisticated, deformable mirror about the size of the palm of your hand. "The end result is," says Herriot, "images that rival or even exceed the sharpness of pictures taken from space."
Working with Gemini Observatory personnel, the Canadian team headed by Project Manager Herriot and Project Scientist Dr. Jean-Pierre Veran, have been commissioning Altair on Gemini North from late 2002 through early 2003. The instrument team, comprised of 25 scientists and engineers, guided the Gemini adaptive optics system from design to commissioning over the past six years. "Commissioning a precision instrument on a 7-story, 350- ton, sophisticated telescope is especially challenging because of the extremely intricate coordination required to make all the systems work together seamlessly," said Herriot. Altair's commissioning on Gemini is expected to be complete before the end of 2003.
A key feature of Altair's sophistication is the ability to automatically monitor, adjust and optimize multiple parameters during image exposures. The idea is to make adaptive optics user-friendly for our community. Simply point and click and near diffraction-limited images are delivered to your camera or spectrograph. Altair continually measures and reports on the images' level of detail making it one of the most efficient adaptive optics systems in the world. "By routinely delivering infrared images much sharper than is currently possible even from space, Altair gives observers a tremendous advantage in probing deeper in the universe and making more accurate measurements of astronomical objects," Dr. Veran says.
"Altair enormously enhances the quality and power of our imaging and spectroscopy," says Dr. Matt Mountain, Gemini's Director. "Gemini will soon deliver diffraction- limited images in the near-infrared." Gemini's theoretical diffraction limit (maximum resolution) is about 40 milli- arcseconds in the near-infrared H-band (1.6 micrometers wavelength). At this point in commissioning, Altair can deliver 60-milli-arcsecond resolution in the H-band (60 milli-arcseconds is comparable to viewing one grain of sand from about 1.6 kilometers or 1 mile away).
Dr. Mountain pointed out that Altair's commissioning means that one of the most sophisticated adaptive optics system in the world is now built-in to Gemini North as a facility instrument, and will soon be routinely available to all scientists throughout the Gemini partnership.
"This is a major achievement towards our Gemini goal of delivering space-quality images from an 8-meter, ground- based telescope," said Dr. Mountain.
Gemini's Associate Director Dr. Jean-Rene Roy explains that Altair is a major step forward in Gemini's aggressive plans to maximize the potential of adaptive optics on ground-based astronomical imaging. Dr. Roy elaborates, "Altair, representing the foundation of tomorrow's adaptive optics technology, is important for the success of the next generation of 30- to 100-meter, diffraction-limited, infrared, ground-based telescopes now on the drawing boards."
Future generations of adaptive optics technologies like these will undoubtedly revolutionize ground-based astronomy. For now, Altair is state of the art and provides a powerful new eye on the universe.
The Gemini Observatory is an international collaboration that has built two identical 8-meter telescopes. The Frederick C. Gillett Gemini Telescope is located at Mauna Kea, Hawaii (Gemini North) and the other telescope at Cerro Pachon in central Chile (Gemini South), and hence provide full coverage of both hemispheres of the sky. Both telescopes incorporate new technologies that allow large, relatively thin mirrors under active control to collect and focus both optical and infrared radiation from space.
The Gemini Observatory provides the astronomical communities in each partner country with state-of-the-art astronomical facilities that allocate observing time in proportion to each country's contribution. In addition to financial support, each country also contributes significant scientific and technical resources. The national research agencies that form the Gemini partnership include: the US National Science Foundation (NSF), the UK Particle Physics and Astronomy Research Council (PPARC), the Canadian National Research Council (NRC), the Chilean Comision Nacional de Investigacion Cientifica y Tecnologica (CONICYT), the Australian Research Council (ARC), the Argentinean Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET) and the Brazilian Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq). The Observatory is managed by the Association of Universities for Research in Astronomy, Inc. (AURA) under a cooperative agreement with the NSF. The NSF also serves as the executive agency for the international partnership.
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