Granulation patterns in LTT 9779 and WASP 121 revealed by JWST

Researchers used the JWST to observe the granulation on the surfaces of stars LTT 9779 and WASP 121. Granulation is the visible pattern of energy rising and falling on a star's surface. By studying how this light flickers across different wavelengths, they measured the amplitude and duration of these convective cycles, providing new insight into the small-scale stellar activity that can interfere with exoplanet observations.

Star system: LTT 9779 | Distance from the Sun: 264 light years

Stars are not perfectly static spheres of light. Their surfaces are covered in granulation, a boiling pattern caused by heat rising from deep within the star and cooling as it reaches the surface. These granules appear as bright, shifting cells that create constant, tiny flickers in a star's brightness. Understanding these rapid fluctuations is essential because they can mimic or mask the faint signals of orbiting planets.

By analyzing high-precision data from the JWST, researchers measured the intensity and duration of these granulation patterns for two specific stars, LTT 9779 and WASP 121. They first removed the signals caused by the orbiting planets, such as eclipses and phase changes, to isolate the pure stellar signal. They then used a statistical method called a power spectrum to track how quickly the stars brighten and dim. By breaking this light into specific color channels, they also determined how these fluctuations change across different wavelengths of near-infrared light.

This analysis showed that the intensity of these brightness variations decreases as the wavelength of light increases. Measuring these specific patterns helps refine how astronomers filter out stellar noise. By identifying the unique flicker of a star, researchers can more accurately distinguish between signals originating from the star itself and those coming from the thin atmospheres of distant planets.

Key findings
LTT 9779 exhibits a granulation amplitude of 53.8 parts per million with a cycle timescale of 4.8 minutes.
WASP 121 shows a granulation amplitude of 59.3 parts per million with a cycle timescale of 6.3 minutes.
Peak oscillation frequencies were measured at 3382 microhertz for LTT 9779 and 1649 microhertz for WASP 121.
The amplitude of granulation-induced brightness variation decreases toward longer wavelengths of light.

Scientific study

Granulation in Color: The Chromatic Stellar Flicker of LTT-9779 and WASP-121 (external link)