IU East Astronomer Publishes Rare Finding in Binary Stars

March 22, 2024 |

As an astronomer, IU East faculty member Wes Tobin’s laboratory is a telescope with which he observes distant star systems.

His specialty is contact binary stars, consisting of two stars that orbit each other so closely that their surfaces touch.

Tobin’s most recent discovery involves the binary system NSVS 2910034.

This star system, found in the constellation Draco, is highly unusual. Its two stars are approximately equal in size. They orbit each other approximately three times each day.

One would usually expect these two stars to eclipse each other at regular intervals, leading to a predictable pattern in changing brightness as observed through a telescope,” Tobin explained.

Tobin’s exhaustive observations of more than 2600 eclipses, through the space-based telescope TESS (the Transiting Exoplanet Survey Satellite) and ground-based telescopes, revealed something unexpected: Instead of finding predictable patterns in changing brightness, Tobin’s observations revealed almost random patterns in the dimming and brightening as one star passes in front of the other.

The two stars are nearly the same size, and each is slightly less than the mass of our own Sun. They are also slightly cooler than the Sun at 5200 K and 5570 K.

The two stars are so close to one another that they share their atmosphere through a small bridge connecting the stars. According to Tobin, this bridge allows the two stars to exchange material between them. However, the close proximity and shared atmosphere alone do not explain the unpredictable pattern.

Tobin’s computational models of the observations revealed the cause: The cooler star has an unusually large hot spot, which is the cause of the unpredictable timing of the eclipses.

This hot spot covers almost half of the surface of this star. While the hot spot explains the irregular pattern of the eclipses, Tobin cannot yet explain the origin of the hot spot itself.

“Such large hot spots are exceptionally rare, with fewer than a dozen similar systems previously discovered,” Tobin explained.

“Typically, a hot spot in a binary system is small and is created when gas escapes one star and then falls directly onto the surface of the other star. This impact creates a small hot spot. However, a large hot spot cannot be produced this way. We believe that large hot spots are created by strong magnetic fields in cooler stars with strong convection zones. Still, our understanding of stellar interiors does not entirely explain this phenomenon, making it especially exciting to discover,” Tobin said.

Tobin’s results will be published in a forthcoming article, “Photometric Study of the Overcontact Binary NSVS 2910034,” in the July 2024 issue of the journal New Astronomy.

Markus Pomper, the dean of the School of Natural Science and Mathematics, is excited about Tobin’s success and recognition as an astronomer.

“Even though we are a small campus, our faculty are active scholars who produce remarkable results,” Pomper said. “Our students have the opportunity to learn in a small campus environment, yet they have access to the computational resources at Indiana University and active scholars whose discoveries are published in reputable journals.”