Daily Image
11-12-2007
First Ground-Layer Adaptive-Optics System for General Astronomical Observations
| Submitter: | Ton Schoenmaker |
| Description: | A new 'ground-layer adaptive-optics' system (GLAS) has been commissioned at the William Herschel Telescope on the island of La Palma. It will permit astronomers to study celestial objects in much greater detail. It is the first system in the world that will be used for general astronomical observations. It was developed by the Isaac Newton Group of Telescopes, in collaboration with scientists from Durham University (UK), the University of Leiden (Netherlands) and the ASTRON institute (Netherlands), The GLAS works with a high-tech pulsed laser. The left-hand picture by Javier Méndez shows the laser beam emerging from a small telescope mounted behind the secondary mirror of the William Herschel Telescope. It is reflected from a layer in the atmosphere at an altitude of 15 kilometers. The light from this artificial 'star' is detected by a sensor that measures the atmospheric distortions. This information is used at a rate of several hundred times per second to shape a rapidly adjustable deformable mirror to take out the adverse effects of atmospheric turbulence. This is called 'ground-layer' adaptive optics because the somewhat low altitude of the artificial star implies that air turbulence near to the ground (i.e.< 100m) is preferentially illuminated and corrected. It takes care of the largest (and slowest) component of astronomical 'seeing'. The picture in the middle/right, by René Rutten, Javier Méndez and the GLAS commissioning team, shows a comparison of H-band images of Uranus with GLAS and adaptive optics correction off and on. The faint point at the bottom is the moon Miranda. The 'heat'-coloured picture shows a comparison of an uncorrected and laser-corrected image of the globular cluster M15. The images are 5 by 6 arcseconds wide, and the laser correction improved the quality from 0.40 to 0.16 arcseconds. |
| Copyright: | Isaac Newton Group of Telescopes, La Palma |
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