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 Thursday February 28, 2002
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The recently discovered brown dwarf is located in the constellation Sagitta. It orbits a star not unlike our own sun.


UH astronomer finds rare star
Discovery made with Hawai'i telescopes using new technology

By Mia La Londe
Ka Leo Contributing Writer

February 28, 2002

New celestial bodies have come into view, thanks to recent developments in telescope optics, said a University of Hawai'i astronomer.

Michael Liu gave a lecture Tuesday night on his recent findings on brown dwarfs, also known as failing stars; the use of adaptive optics in telescopes; and the discovery of planets in other solar systems, known as extra-solar planets.

"In the last few years, observational astronomy has undergone a revolution. We are now able to study, observe and characterize worlds around other stars," said Liu.

Liu and his colleagues announced the discovery of a brown dwarf at the meeting of the American Astronomical Society in January 2002.

Liu found the brown dwarf using the Gemini North telescope and the Keck telescope on Mauna Kea. Both of the telescopes use a technology called an adaptive optics system.

Adaptive optics sharpen images which would normally be blurred due to the turbulence of Earth's atmosphere, said Liu. Telescopes using adaptive optics are able to make some images sharper than those produced by the Hubble Space Telescope, he said.

Liu said the use of adaptive optics was instrumental in the discovery of the brown dwarf. "It is too faint and too close to its parent star to be seen otherwise," he said. "If you were standing on Diamond Head looking at your friend standing on Mauna Kea, you would be able to tell if they were wearing gloves. That's how powerful they are."

Brown dwarfs are believed to be categorized between planets and stars. They start out with high temperatures comparable to stars, but cannot sustain nuclear fusion like stars do.

"Brown dwarfs start off very bright, then cool off. They get ever fainter, ever dimmer and ever cooler," he said.

Brown dwarfs have masses 55 to 78 times the mass of the planet Jupiter, the largest planet in our solar system. Jupiter is about 300 times larger than the earth.

According to Liu, since brown dwarfs are more massive than planets, they cause more tugging on the main star, which makes them easier to detect than planets.

"Despite the fact that they are easier to detect, we don't see any brown dwarfs and it is a bit of a mystery. It is something that astronomers are calling a brown dwarf desert," he said.

The brown dwarf Liu found is located in the constellation Sagitta around a star known as 15 Sge., which is very similar to our own sun.

Liu said the star is relatively nearby: approximately 58 light-years from Earth. "Its age is 1 to 3 billion years old, which is slightly younger than our solar system which is about 5 billion years old," he said.

The brown dwarf lies 14 astronomical units away from its parent star, 15 Sge. One astronomical unit is the distance between the earth and the sun; this is equal to 93 million miles.

Until 1995, the planets that rotated around the sun in this solar system were the only basis that astronomers had to theorize about planets around other stars.

"In 1995 everything changed for astronomy. They had found a planet circling a star just like our own sun," Liu said.

Scientists have since discovered many planets and say that those solar systems are not unlike our own. Five percent of the stars they have observed have planets and some of those stars have more than one planet. There are currently 80 known extra-solar planets, said Liu.

Scientists cannot detect a planet of Earth's size using current techniques but according to Liu, they they soon may be able to infer the existence of Jupiter-sized planets.

Mauna Kea is a world-class site for astronomy, said Liu. On Mauna Kea, there are currently 11 telescopes, which are operated by astronomers from 11 different countries. If measured from its base beneath the ocean, Mauna Kea is the highest mountain in the world. It rises 32,000 feet, to an altitude of 13,976 feet above sea level. The atmosphere above Mauna Kea is extremely dry, which is important in measuring infrared light from celestial sources. Liu called the view from Mauna Kea "a spectacular sight."

Liu is the Beatrice Watson Parrent Postdoctoral Fellow of the Institute for Astronomy and UH. Parrent Fellows are given two years of funding for their choice of study. The funds can be extended to a third year at the discretion of the director of the Institute for Astronomy.

Liu received his doctorate in physics and astronomy from the University of California at Berkeley.  end of article dingbat


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