This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Astronomers using Georgia State University's Center for High Angular Resolution Astronomy (CHARA) Array have found that nearby stars darken toward their edges more strongly at near-infrared wavelengths than predicted by several widely used models of stellar atmospheres, providing a new benchmark for understanding how stars are structured. The research team measured how the brightness of 31 nearby stars changes from the center of each stellar disk to its edge.
This effect, known as limb darkening, makes a star appear fainter at its edge than at its center. The observations show that limb darkening changes more strongly at near-infrared wavelengths than predicted by several widely used stellar-atmosphere models. Limb darkening appears because stars are not uniformly bright disks.
Light from near the center of a stellar disk comes from deeper, hotter layers of the atmosphere, while light from the edge comes from shallower, cooler layers and passes through more stellar material. "We are not just measuring how large these stars are," said lead author Narsireddy Anugu, a staff scientist at Georgia State University's CHARA Array. "We are measuring how their light is distributed across the stellar disk, which directly tests stellar-atmosphere models." By observing the same stars simultaneously using two different near-infrared filters, the team measured how the center-to-edge fading changes with wavelength.
As expected, the researchers found that limb darkening is weaker at longer wavelengths. However, the measured change was larger than predicted by several commonly used stellar-atmosphere models. "This study demonstrates the powerful capabilities of our facility," said Gail Schaefer, director of the CHARA Array.
"By combining light from telescopes across the mountaintop, we can image stars with enough detail to see what their surfaces actually look like." Located on Mount Wilson in California, the CHARA Array combines light from six telescopes positioned at different sites across the observatory grounds. By combining the light to produce interference, CHARA achieves the resolving power of a much larger telescope. Rather than capturing direct images of stars, CHARA measures how the contrast of the interference pattern changes with the spacing between telescopes.
These measurements reveal both the size of a star and how the brightness changes across its surface. The survey focused on 31 bright stars in late stages of their lives, when their outer layers have expanded outward. These evolved subgiant, giant and supergiant stars provide especially valuable tests of stellar-atmosphere models because the large convective motion in their extended atmospheres can produce complex brightness profiles.
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