Saturday, April 5, 2008

Clearing the Air

Ground-based telescopes are entering into a new era with adaptive optics (AO) technology providing sharper views of the universe than ever before. AO allows astronomers to remove the blurring effects of Earth's atmosphere in real time.

The adaptive optics program at Palomar is more than a decade old. In October 2004 we added a new dimension to the program and achieved first light with the laser-guide star (LGS) system. LGS allows astronomers to create an artificial star and use AO in a much larger fraction of the sky.

To do this they shine a narrow sodium laser beam up through the atmosphere. At an altitude of about 60 miles the laser makes a small amount of sodium gas glow. The reflected glow from the glowing gas serves as the artificial guide star for the AO system. The laser beam is too faint to be seen except by observers very close to the telescope, and the guide star it creates is even fainter. It can't be seen with the unaided eye, yet it is bright enough to allow astronomers to make their AO corrections.

The technology is involved. Early on all the time devoted to it is what we call engineering time. Basically that is time on the telescope to tinker, measure and improve all in the name of getting ready for the real astronomical observations that are to follow.

Following that is what is known as shared-risk science. During this time astronomers come to use the LGS system to do real astronomical observations, but with the knowledge that there will still be some time devoted to engineering mixed into the night.

One year ago today was the first night of shared-risk science with Palomar Observatory's laser-guide star adaptive optics program. Caltech professor Lynne Hillenbrand and graduate student Adam Kraus where here to use laser and natural guide Star adaptive optics to conduct a high-resolution imaging survey of young low-mass stars and brown dwarfs in several nearby young associations.

JPL astronomer Patrick Lowrance was back later in the month for another LGS night to study L, T, and brown dwarfs. The time-lapse movie below shows approximately 3 hours of LGS operations during a night as photographed from outside the Hale Telescope dome.


Each frame in the silent movie was a 30-second exposure. Along with the laser, stars and airplanes are visible in the sky.

More photos, movies and information is available on the Palomar Observatory Adaptive Optics page.

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