College of Liberal Arts and Sciences at Iowa State University

Star dust

Lee Anne Willson continues long-term research of the origin of space dust.

Lee Anne Willson has been working for 35 years to understand the stars that produce space dust.

That dates back to graduate school for the University Professor of physics and astronomy.

"It was clear when I was in graduate school that some stars consistently lose mass in their evolution," she said. "It just wasn't clear when and how that happens."

Calling her work "stellar gerontology," Willson studies red giants - the stars that expand and burn red and relatively cool as they move through the final stages of their life cycles.

In the 35 years since she first started her research in this area, the field has changed vastly Willson says. Early on there was nothing in the data showing stars were losing mass at all.

Because of that Willson was among the few astronomers actually studying this area.

"There were only three or four scientists interested in this when I came along," she said. "That has changed now because of technology. A lot of new data came with infrared and ultraviolet telescopes in space. People now also realize the evolutionary role of these stars.

"That made the subject much more interesting to people."

Computer modeling developed in the late 1970s has also increased the knowledge of the red giants. Emeritus professor G. H. Bowen produced models incorporating some of Willson's insights, and these models have led to more understanding.

"We now have models we can work with," Willson said. "When we analyze the models we can determine the mass loss of the stars."

Willson recently presented some of her findings at the Annual Meeting of the American Association for the Advancement of Science. She also addressed and helped organize a press briefing at the meeting titled, "Stardust: Solar System Birth and Death."

Some of Willson's findings indicate that the origins of space dust are red giant stars characterized by:
- Super size. Their stellar radius is about the size of earth's orbit.
- Changing brightness. Their brightness varies dramatically over the course of a year-long cycle.
- High luminosity. They radiate several thousand times more power into space than the sun.
"The variability of those stars is fundamental to dust formation," she said. "The variability produces shock waves which compress the gas. It radiates away some heat and then cools quickly as it expands again before the next shock passes.It's a refrigerator."

This creates conditions that allow dust formation closer to the star than would otherwise be possible.

"These dust particles start their journeys in my stars and end up in the solar system," she said.

And although she has worked on other astronomy problems, the red giants are her favorite area of research.

"This (project) has sustained my interest the most over the years," she said. "There's nothing quite as much fun for a scientist as working on a challenging problem.

"There comes a moment when you suddenly realize there is another way at looking at the problem that makes sense and all the pieces fall into place."