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<A Glimpse at the Future of Our Sun ⁄ >




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A team of astronomers recently used Arizona's Infrared-Optical Telescope Array (IOTA) of three linked telescopes to peer 4 billion years into the future, when our Sun balloons up to become a red giant star. The three instruments act as a powerful interferometer, providing a view that would only be possible with a much larger instrument. They observed several red giant stars - the eventual fate of our Sun - and discovered their surfaces to be mottled and varied, covered with enormous sunspots.

As astronomers increasingly link two telescopes as interferometers to reveal greater detail of distant stars, a Keck Observatory astronomer is showing the power of linking three or even more telescopes together.

Astronomer Sam Ragland used Arizona's Infrared-Optical Telescope Array (IOTA) of three linked telescopes to obtain unprecedented detail of old red giant stars that represent the eventual fate of the Sun.

Surprisingly, he found that nearly a third of the red giants he surveyed were not uniformly bright across their face, but were patchy, perhaps indicating large spots or clouds analogous to sunspots, shock waves generated by pulsating envelopes, or even planets.

"The typical belief is that stars have to be symmetric gas balls," said Ragland, an interferometer specialist. "But 30 percent of these red giants showed asymmetry, which has implications for the last stages of stellar evolution, when stars like the Sun are evolving into planetary nebulae."

The results obtained by Ragland and his colleagues also prove the feasibility of linking a trio - or even quintet or sextet - of infrared telescopes to get higher resolution images in the near-infrared than has been possible before.

"With more than two telescopes, you can explore a totally different kind of science than could be done with two telescopes," he said.

"It's a big step to go from two telescopes to three," added theoretician Lee Anne Willson, a coauthor of the study and a professor of physics and astronomy at Iowa State University in Ames. "With three telescopes you can tell not only how big the star is, but whether it's symmetric or asymmetric. With even more telescopes, you can start to turn that into a picture."

Ragland, Willson and their colleagues at institutions in the United States and France, including NASA, reported their observations and conclusions in a paper recently accepted by The Astrophysical Journal.

Ironically, the IOTA telescope array, operated jointly on Mt. Hopkins by the Smithsonian Astrophysical Observatory, Harvard University, the University of Massachusetts, the University of Wyoming, and the Massachusetts Institute of Technology's Lincoln Laboratory, was shut down July 1 to save money. The initial two-telescope interferometer went online in 1993, and the addition of a third 45-centimeter telescope in 2000 created the first optical and infrared interferometer trio.

IOTA director Wesley A. Traub, formerly of the Harvard-Smithsonian Center for Astrophysics (CfA) and now at the Jet Propulsion Laboratory, offered Ragland and his colleagues the opportunity to use the array to test the limits of multiple-telescope interferometry, and perhaps learn something about the ultimate fate of the Sun.



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