Sunlike Star Vibrations Seen for First Time

Anne Minard

A first look at the surfaces of three nearby stars shows that the hot bodies are vibrating faster than our sun and have smoother exteriors, according to new research.

The work could help astronomers get a better picture of minute changes in stellar vibrations, which would improve our understanding of how sunlike stars operate inside.
Also, knowing more about subtle changes in the surfaces of other stars can help scientists better predict sun storms, which can damage orbiting satellites and interrupt power lines on Earth.

Studies of the sun's vibrations, or helio-seismology, have been yielding clues about our star's interior structure for decades. (Related: "Sun Gets Fatter 'Waist' During Magnetic Peaks" [October 2, 2008].)

Granulation, or bubbling, of the stellar surface can reveal how heat is being transported through the uppermost layers of gas.

But until recently, vibrations and surface features in more distant stars have been too hard to detect, so scientists have relied on computer simulations based on data from the sun.

"In the last few years, observers have started to see acoustic spectra from solar-type stars that are comparable in quality to what was seen in the sun nearly 30 years ago," said Rachel Howe, a scientist at the National Solar Observatory in Tucson, Arizona, who was not involved with the new study.

"These measurements will allow observers to probe the rotation and other properties of stars that are similar to our sun but of different sizes and ages."

Lead study author Eric Michel, a stellar physicist with France's National Center for Scientific Research, said his team's data should help refine previous computer predictions.

"The phenomena we observe are of the order of what we expected, and we will be able to measure them with precision," Michel said via email. "We are now looking into the stars!"

Margin of Error

All three stars observed for the new study are within 200 light-years of Earth. They are similar to the sun but are hotter and slightly more massive.

Using France's Convection Rotation and Planetary Transits (CoRoT) space telescope, Michel and a bevy of colleagues from Europe and South America measured the stars' light output over a 60-day period.

CoRoT reads stellar vibrations as changes in brightness.
The team found that the three stars have vibrations that are 50 percent more energetic than the sun's.

The stars also have surface granulations about three times finer than the sun's.

The observed oscillations are close to what astronomers predicted based on computer models, but are about 25 percent weaker than expected.

"This is not so bad and even gratifying," Michel said, adding that the results fall within the margins of uncertainty built into the models.

The data are described in this week's issue of the journal Science.

The study authors add that the results would not have been possible using observatories on the ground, because Earth's atmosphere obscures minute variations in starlight.

For them, the new data illustrate the importance of continued space-based observations.

(See the first 3-D images of the sun taken in 2007 by a pair of orbiting telescopes.)

Michael Montgomery, a stellar physicist at the University of Texas in Austin, wrote a commentary on the new study that also appears this week in Science.

"This [paper]," he said, "bodes well for the future of space-based seismology programs while simultaneously challenging us to refine our models of these stars."