By Patricia Daukantas
For the past decade, astronomers have used laser guide star (LGS) adaptive-optics systems to remove the blurring caused by atmospheric turbulence above ground-based telescopes. Such systems, however, have always faced one restriction: an extremely narrow field of sharp viewing.
A team from the University of Arizona (Tucson, U.S.A.) has managed to widen that sharp field by developing a five-laser guiding system for the MMT telescope on Mount Hopkins in southern Arizona. The astronomers report on their system in the August 5 issue of Nature.
Michael Hart, of the university’s Steward Observatory, and colleagues wanted to study aging star clusters at near-infrared wavelengths (1.25 to 2.2 μm). One such cluster, dubbed M3, nearly fills the 110-arcsecond-wide field of the MMT’s infrared camera.
The researchers arranged five 4-W, 532-nm pulsed lasers in a pentagon and projected them from a small telescope behind the MMT’s adaptive secondary mirror. A combination of three sensors detects the aberrations in the Rayleigh-backscattered light coming back to the telescope, estimates the aberration from ground-level turbulence and directs the secondary mirror to correct the aberrations.
On a night when the native “seeing,” or point-spread-function diameter of stellar images, at the MMT was only 0.7 arcseconds, the astronomers improved it to 0.3 arcseconds over a 2-arcminute-wide field of view – roughly the same as the Hubble Space Telescope gets with its most recent upgrades, but with a bigger aperture to gather more light.
Astronomers are now developing a similar system for the Large Binocular Telescope on Arizona’s Mount Graham.
2010-08 August, Astronomy, Lasers