Seeing Starspots
Ohio Wesleyan Professor, OWU Alumna Earn NASA Grant to Research Stellar Magnetic Activity, Impact
DELAWARE, Ohio – Ohio Wesleyan University astronomy professor Robert Harmon and 2008 OWU graduate Rachael Roettenbacher, assistant research scientist at the University of Michigan, have received a $600,000 NASA grant to conduct what Harmon calls "the largest-scale study of starspots performed to date in terms of the number of stars involved."
"Studies of starspots provide important insights into the physics of stellar magnetic fields and how they are generated," said Harmon, Ph.D., a member of the Ohio Wesleyan faculty since 1999. "This, in turn, provides insight into magnetic processes on the Sun, which are important to understand because the Sun's magnetic field is the driver of solar storms and coronal mass ejections that can have profound consequences for electrical grids, satellites, and more."
Harmon is using a portion of the three-year NASA grant to hire two OWU students each summer from 2025 through 2027. The students are assisting Harmon and Roettenbacher in their starspot studies through Ohio Wesleyan's annual 10-week Summer Scholarship and Research Program (SSRP).
Roettenbacher, Ph.D., who is the grant's principal investigator, began her own research into starspots during her time as an Ohio Wesleyan astrophysics and mathematics double major. After graduating cum laude from Ohio Wesleyan, Roettenbacher earned a Master of Science in Physics from Lehigh University and both her Master of Science and her doctoral degrees in Astronomy and Astrophysics from the University of Michigan.
"Rachael and I studied starspots on a star named LO Pegasi when she completed an OWU research project with me back in 2006," Harmon said. "She and I have been collaborating on starspot research and publishing papers together ever since, and this is our biggest project yet. It's a pleasure to have your former student become your colleague, your collaborator, and your friend."
Their project, "Determining How Stellar Activity Depends on Stellar Parameters," continues to map starspots using a light curve inversion technique that Harmon developed.
"Here, 'stellar activity' refers to stellar magnetic activity as manifested in starspots, which are darker regions on a star's surface that are similar to sunspots on the Sun – sunspots are just solar starspots. 'Stellar parameters' refer to properties such as the star's mass, radius, surface temperature, age, and rotation rate," he explained.
"Rachael and I, and the OWU students working with us, are accomplishing this by using data from the Kepler space telescope. It was launched in 2009 as NASA's first mission to study exoplanets, which are planets orbiting stars other than the Sun."
While searching for exoplanets, he said, the Kepler telescope detected starspots on more than 40,000 stars.
"Starspots are regions on a star's surface where strong vertical magnetic fields suppress the transport of heat toward the surface from hotter layers below, causing the spots to be cooler and thus darker than the rest of the star's surface," Harmon explained. "The Sun is the only star close enough for us to obtain detailed images of its surface features. Other stars are so far away that most look like pinpoints even to the most advanced telescopes, so we must resort to indirect techniques to determine what their surfaces look like.
"As the star's rotation carries its dark starspots into and out of view of Earth, the star's brightness varies as a result," he said. "I developed a computer program that takes the brightness variations as input and generates a rough map of the distribution of starspots on the star's surface as output. Students working on the project are assisting in analyzing how the starspot distribution and the way it changes over time depend on other stellar characteristics, giving important clues into the behavior of stars' magnetic fields and how they are generated."
Roettenbacher said she is excited to collaborate on the NASA-funded research with Harmon and Ohio Wesleyan students.
"We wrote the grant to include funding specifically for OWU students because it is meaningful to me to help provide the opportunity to work on research, as the SSRP was a wonderful experience for me," she said. "I continue to be grateful to have had that opportunity to work with Bob and to be exposed to astronomy research for the first time."
Learn more about Harmon and Ohio Wesleyan's Department of Physics and Astronomy at owu.edu/physics and more about the university's annual Summer Scholarship and Research Program at owu.edu/SSRP.
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