Oscillation patterns in Gliese 570 A and Gliese 783 A reveal new stellar physics

Researchers have used high-precision radial velocity measurements to analyze solar-like oscillations in two orange dwarf stars, Gliese 570 A and Gliese 783 A. The data reveals that these stars exhibit a steeper oscillation amplitude scaling than current theoretical models predict, highlighting a significant gap in our understanding of how energy moves through the outer layers of these types of stars.

Star system: 33 G. Librae A | Distance from the Sun: 19.2 light years

Stars like the Sun generate oscillations, or rhythmic vibrations on their surface, caused by the turbulent motion of boiling gas in their outer layers. While these vibrations are easy to measure in Sun-like stars, they are much harder to detect in orange dwarfs because the signals are very faint. To overcome this, high-precision tools can now measure tiny shifts in a star's light caused by these movements, a technique known as Doppler asteroseismology. This approach allows for a direct look at the interior physics of stars that are cooler and smaller than the Sun.

To study these vibrations in Gliese 570 A and Gliese 783 A, the ESPRESSO instrument collected continuous data over several consecutive nights. By creating weighted power spectra, which represent the strength of different oscillation frequencies, researchers identified individual vibration modes. These observed results were then compared against complex three-dimensional computer simulations that model how heat moves through a star's surface. These simulations are intended to predict the strength of stellar oscillations based on the star's mass and luminosity.

The findings show a clear discrepancy between observations and theory. While existing models suggest a specific scaling relationship for oscillation strength, the measured data for these orange dwarfs indicates a much steeper trend. This suggests that current simulations may be missing critical details about how stellar pulsations couple with convection, which is the process of heat transfer in the outer layers. These results demonstrate the need for more refined models to accurately describe the complex behaviors occurring within these stars.

Key findings
Detected 6 oscillation modes in Gliese 570 A and 24 modes in Gliese 783 A.
Measured peak radial-mode amplitudes of 2.57 centimeters per second for Gliese 570 A and 4.90 centimeters per second for Gliese 783 A.
Observed a steep amplitude scaling of approximately 1.5 in the ratio of luminosity to mass.
Identified a conflict between real-world observations and 3D convection simulations, which predicted a lower scaling of 0.9.

Scientific study

EPRV Asteroseismology of the K dwarfs GJ 570 A and GJ 783 A with ESPRESSO. Empirical mode-amplitude scaling in tension with 3D convection simulations (external link)