Emory Report
July 7, 2008
Volume 60, Number 34



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July 7, 2008
Cosmic sleuths’ routine sky surveillance reveals celestial discovery


When most people look into the sky on a clear, moonless night, they just see a bunch of stars. Horace Dale sees individuals.

“Each star has its own personality, that’s for sure,” says Dale, an astronomer and physics research associate.
He’s particularly fond of one that was previously listed in the General Star Catalog as GSC 4014-1629. This past fall, Dale and students in his advanced astronomy class were the first to discover that it is a variable star — one that changes its luminosity over short periods of time. In layman’s terms: It twinkles. And we’re talking a true twinkle, as opposed to the false twinkle-effect that the Earth’s atmosphere gives stars.

“It’s cosmic detective work,” Dale says of the find. “You have to understand the nature of light.”

A little luck also helps. Dale freely admits that the discovery probably wouldn’t have happened if he hadn’t dozed off. “That was kind of serendipitous,” he says.

The idea was to set up a routine lab exercise for his students to study a known variable star. It’s a time-consuming lab procedure to measure changes in a star’s brightness. A full night’s worth of data must be gathered and tested beforehand for comparison purposes. Dale pulled the necessary overnighter to get it.
He chose a variable star in the constellation of Cassiopeia and aimed the observatory’s telescope at it. He attached a digital camera to the scope and set up shop in the control room below. A computer and special software allowed him to measure the changing brightness of the variable star over time, using the brightness of five nearby stars that were not variables as references for constant luminosity.

All went well until around 2 a.m., when Dale fell asleep for about 80 minutes. When he awoke, he realized that the telescope had drifted, leaving only a single reference star, GSC 4014-1629, in the field of view. One reference star was enough for his purposes, but Dale needed to pull another night at the lab, to fill in the missing minutes of data.

He later compared the data from both nights on his laptop, while sitting at home in his La-Z-Boy. His wife was in the room when Dale had his eureka moment — he saw that the reference star had slightly changed its luminosity during that brief gap in time. “I knew right away we had a variable,” he recalls. “I said, ‘Wow! Look at this!’ My wife said, ‘Yeah, hon. That’s nice.’”

Dale’s students responded with more enthusiasm. “It was an incredible teaching tool,” he says, explaining that he presented the students with the comparative data to use in the lab. Through their own analyses they recognized that the reference star was actually a variable.

Dale and the students submitted their results to the International Variable Star Index which confirmed the discovery, and gave the star the new designation of J001528.0+602037.

Further study showed that the star is one of only 400 known Delta Scuti pulsating variables — an older star with gases that are rapidly expanding and contracting in both spherical and oblong shapes. The star is slightly hotter than the sun, one-and-a-half times as big, and located about 2,000 light years from Earth.
“It’s amazing to me that we can come up with all of these conclusions just through our knowledge of light,” Dale says. “Light is the only thing astronomers have to work with, but when you understand the nature of light, you can literally see back in time.”

Out of the billions of stars in our galaxy, only about 43,000 variable stars have been identified and classified, although many more are out there. You can bet Dale and his astronomy students will be scoping the night skies for another one.

“It’s really important that we study them,” Dale says, explaining that variable stars have helped us learn about stellar evolution and the size of our galaxy. “The more of them we have to study, the more we can know. It tells us something about who we are and why we’re here.”