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Star near Southern Cross is ringing like a bell ANGLO-AUSTRALIAN OBSERVATORY NEWS RELEASE Posted: January 1, 2006 Astronomers have used the Anglo-Australian Telescope in Australia and European Southern Observatory's Very Large Telescope in Chile as a 'stellar stethoscope' to 'hear' -- more clearly than ever before -- a star that is ringing like a bell.
"The trick was to use two telescopes at essentially the same time." The researchers, led by Bedding and Dr Hans Kjeldsen (Aarhus University, Denmark), studied the star alpha Centauri B, one of the stars of the 'Pointers' near the constellation of the Southern Cross. Over a week they observed the star with both the 3.9-m Anglo-Australian Telescope near Coonabarabran in New South Wales, Australia, and Kueyen, one of the four 8.2-m telescopes that make up the European Southern Observatory's Very Large Telescope at Cerro Paranal in Chile. The team measured the rate at which the star's surface is heaving in and out, getting clues about the density, temperature, chemical composition and rotation of its inner layers -- information that could not be obtained in any other way. The research was published in the Astrophysical Journal. Alpha Centauri is the brighter of the two 'Pointers' near the constellation of the Southern Cross. It's not one star but three: they are the closest stars to Earth, about 4.3 light-years away. Alpha Centauri B is an orange star, a little cooler and a little less massive than the Sun. Churning gas in the star's outer layers creates low-frequency sound waves that bounce around the inside of the star, causing it to ring like a bell. This makes the star's surface pulsate in and out by tiny amounts -- just a dozen meters or so every four minutes. Because the surface is moving, the light coming from it is very slightly altered in wavelength, by the effect called the Doppler shift. Astronomers can detect such a change and use it to measure the surface's movement. The researchers sampled the light from alpha Centauri B once a minute for seven nights in a row, making more than 5,000 observations in all. A star's surface can oscillate in many different patterns, or modes, simultaneously. The researchers were able to determine 37 modes of oscillation in alpha Centauri B. They also measured the mode lifetimes (how long the oscillations last), the frequencies of the modes, and their amplitudes (how far the surface of the star moves in and out). Such measurements are a huge technical challenge. These kinds of oscillations have been studied in only about a dozen stars other than the Sun. The stars' surfaces move slowly: in the case of alpha Centauri B, at the tortoise-like speed of 9 cm [3.5 inches] a second, or about 300 meters [300 yards] an hour. And then there's the sheer distance to the stars. Although alpha Centauri B is one of the closest stars to us, it's still more than 280,000 times further away from Earth than the Sun is. If the Sun were shrunk to the size of a pea, on the same scale alpha Centauri B would be another pea 160 km [100 miles] away. The astronomers borrowed their high-precision measurement technique from the planet-hunters, who also look for slight Doppler shifts in starlight. Renowned planet hunters Paul Butler and Geoff Marcy were members of the team studying alpha Centauri B. "So much of what we think we know about the Universe rests on the ages and properties of stars," said Bedding. "But there is still a great deal we don't know about them." By using two telescopes at different sites the astronomers were able to observe alpha Centauri B as continuously as possible. "That's a huge advantage, because gaps in the data introduce ambiguity," said Bedding. "The success of the observations also depended on the very stable spectrographs attached to the two telescopes -- UVES at the VLT and UCLES at the AAT -- which analyzed the star's light." |
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In our continuing look back at the classic days of the space shuttle program, today we show the STS-41D post-flight presentation by the mission's astronauts. The crew narrates this film of home movies and mission highlights from space shuttle Discovery's maiden voyage in August 1984. STS-41D deployed a remarkable three communications satellites -- a new record high -- from Discovery's payload bay, extended and tested a 100-foot solar array wing and even knocked free an icicle from the shuttle's side using the robot arm.
As the title aptly describes, this movie straps you aboard the flight deck for the thunderous liftoff, the re-entry and safe landing of a space shuttle mission. The movie features the rarely heard intercom communications between the crewmembers, including pilot Jim Halsell assisting commander Bob Cabana during the landing.
On Christmas Eve in 1968, a live television broadcast from Apollo 8 offered this message of hope to the people of Earth. The famous transmission occurred as the astronauts orbited the Moon.
The International Space Station receives its 20th Russian Progress cargo ship, bringing the outpost's two-man Expedition 12 crew a delivery of fresh food, clothes, equipment and special holiday gifts just in time for Christmas.
This movie features highlights of the December 23 rendezvous between the Russian Progress 20P vessel and the International Space Station. The footage comes from a camera mounted on the supply ship's nose.
NASA's Stardust spacecraft encountered Comet Wild 2 two years ago, gathering samples of cometary dust for return to Earth. In this Dec. 21 news conference, mission officials and scientists detail the probe's homecoming and planned landing in Utah scheduled for January 15, 2006.
The first robotic space mission to visit the distant planet Pluto and frozen objects in the Kuiper Belt is explained by the project's managers and scientists in this NASA news conference from the agency's Washington headquarters on Dec. 19.
Scientists marvel at the achievements made by the orbiting Hubble Space Telescope in this produced movie looking at the crown jewel observatory that has served as our window on the universe.