SETI [ASTRO] Astronomer Salvages 'Stellar' Science From Disabled WIRE Satellite

Larry Klaes (
Wed, 28 Jul 1999 08:52:30 -0400

>X-Authentication-Warning: majordom set sender
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>Date: Wed, 28 Jul 1999 0:17:25 GMT
>From: Ron Baalke <>
>Subject: [ASTRO] Astronomer Salvages 'Stellar' Science From Disabled WIRE
>Reply-To: Ron Baalke <>
>University of California-Berkeley
>Contact: Robert Sanders, (510) 643-6998,
>Berkeley, July 27 -- When the Wide-Field Infrared Explorer (WIRE)
>satellite went haywire early this year, NASA and the science community
>wrote it off as a complete and costly loss.
>Where NASA saw disaster, however, Derek Buzasi saw opportunity.
>He immediately approached NASA about using the one instrument aboard
>the spacecraft that still worked, a measly two-inch telescope originally
>intended to aid in pointing the satellite.
>While a two-inch diameter telescope on the ground is little more than a
>toy, in space and above Earth's atmosphere it is capable of doing real
>astronomical research, reasoned Buzasi, a research physicist at the Space
>Sciences Laboratory at the University of California, Berkeley.
>He was right. Not long after NASA gave him access, he was able to observe
>a nearby cool star and record starquakes -- the first time anyone has
>observed such vibrations on a normal, cool star.
>"People have been trying to do this for 30 years," Buzasi said.
>Detailed recording of the frequency and amplitude of brightness changes
>that accompany starquakes can give astronomers a wealth of information,
>from the star's mass and age to its chemical composition deep into the
>"It is a spectacular thing he has done," praised Pierre Demarque, professor
>emeritus of astronomy at Yale University.
>"What he has done can only be done from space -- it's a first. It is the
>beginning of a new field of stellar astronomy: stellar seismology."
>Buzasi has submitted two papers about his technique and the discovery of
>starquakes on the star, alpha Ursae Majoris, to the Astrophysical Journal.
>Alpha Ursae Majoris is a bright yellow giant sitting at the lip of the Big
>Dipper, known since ancient times by the Arabic name Dubhe (DUBB ee).
>Part of a two-star system, it lies about 100 light years from Earth, or
>about 600 trillion miles.
>"It's a really nice instrument," Buzasi said about the star tracker. "I was
>lucky that WIRE retained the full capability of the star tracker and that
>the CCD camera attached to it is better than most star trackers need.
>And WIRE points amazingly well."
>NASA has agreed to let him use WIRE's star tracker through October at
>least. Buzasi is now the sole user of the $73 million satellite, after
>NASA finished some engineering studies of the spacecraft last month.
>His next target is one of Earth's nearest neighbors, alpha Centauri, 4.4
>light years distant and a yellow star similar to our own sun.
>"For us this is the most interesting star," said Demarque, who is eager
>to get Buzasi's data to compare to predictions from his model of how
>stars evolve. "We have made lots of calculations about alpha Centauri
>in hopes someday someone would make these observations."
>Two satellites set to fly in 2001 will carry instruments to look at
>stellar pulsations: the French satellite COROT, designed to study stellar
>COnvection and ROTation as well as search for new planetary systems,
>and the Canadian satellite MOST. Neither would have been able to look
>at alpha Centauri, however.
>"Derek has scooped both of them," Demarque said.
>To study starquakes, Buzasi has only to measure the brightness
>fluctuations of the star, taking measurements ten times each second.
>However, to pluck the periodic variations out of the noise, which is a
>thousand times brighter than the fluctuations, he needs to look for a
>long time, on the order of a month. A typical ground- or space-based
>instrument would never have enough available time to allow this.
>Faced with such difficulties, Buzasi saw the tracking telescope
>aboard WIRE as ideal. Plus it is faster for this purpose than many
>ground telescopes, including the world's largest, the 10-meter Keck
>Telescope in Hawaii.
>"A two-inch aperture above the atmosphere can be better than ten
>meters below it," he said.
>Scientists first observed periodic vibrations or solar quakes on the
>sun in the 1960s, and today they have a very detailed knowledge of
>its regular pulsations. These vibrations are like the ringing of a
>bell, and the longer the period the deeper into the sun's interior the
>pulsation reaches. By studying the brightness fluctuations at many
>frequencies, it is possible to reconstruct the interior composition
>and movement all the way down to the core. The field of
>helioseismology has provided nearly all that's known today about
>the internal composition of the sun, its internal rotation and
>"This is the only way we can see inside a star, and thus the only
>way to test various models of the interior of the sun," Buzasi says.
>For the past thirty or more years, astronomers have been trying
>to measure similar periodic vibrations in stars. To date,
>asteroseismology has succeeded with fewer than 50 stars, all of
>them atypical, unstable and rapidly pulsing stars, or with white
>dwarfs, which can have very large oscillations in brightness.
>Now that Buzasi has been able to measure vibrations in a normal
>star, he is collaborating with astrophysicists at Yale, who have
>created a computer program to model stellar evolution.
>Demarque and colleague David Guenther, associate professor of
>astronomy at Saint Mary's University in Halifax, Nova Scotia, have
>been building models of stellar interiors for years in hopes of
>getting data like this for comparison.
>"We calculate the evolutionary track of stars from their beginning
>until it matches their current observed brightness and temperature,"
>he said. "With alpha Ursae Majoris we weren't too optimistic, but
>we were able to reproduce most of the vibration modes he (Buzasi)
>Demarque, Guenther and Buzasi estimate the star's mass at 4.25
>times that of Earth's sun, with a precision far greater than could
>be obtained by other means.
>The masses of most stars are unknown. Only when they are part of
>a binary star system, as is alpha Ursae Majoris, can astronomers
>use the principles of mechanics to estimate their masses. Alpha
>Ursae Majoris was estimated before to be between four and five
>times as massive as the sun.
>"With Derek's data we derived the mass independently. That's
>exciting!" Demarque said.
>WIRE, put together by scientists at the Jet Propulsion Laboratory
>in Pasadena, was launched by NASA March 4 into a perfect orbit. It
>was outfitted with a 30-centimeter, cryogenically cooled infrared
>imaging telescope designed to gather information on "starburst"
>galaxies, those in which rapid star formation is taking place.
>It also was to study infant galaxies known as protogalaxies.
>Scientists had expected to detect at least 50,000 galaxies during
>a four-month survey of the sky.
>Unfortunately, the telescope was somehow uncovered early and the
>solid hydrogen needed to cool the telescope evaporated in the heat
>of the sun. Without the ability to cool the infrared telescope, it
>was useless. The mission was declared a failure March 8.
>When Demarque was asked recently by a senior advisor to NASA
>whether it was worth the money to let Buzasi continue to use the
>WIRE telescope, he was unequivocal.
>"It is well worth a million dollars," he said. "Derek has made his
>point, his observations have been successful beyond all expectations."
>Derek Buzasi can be reached at (510) 643-8244 or
>Pierre Demarque can be reached at the Center for Solar and
>Space Research at Yale University, (203) 432-3024 or
>For more information on WIRE, check the web page at

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