Quantifying the Strength of the Nonlinear Force in Kepler’s Red Giant Stars 106 views

Red giant stars, which are low-mass stars nearing the end of their nuclear-burning lifetimes, exhibit stellar oscillations as sound and internal gravity waves. Analyzing these oscillation modes allows astronomers to infer a star’s internal structure. Data from the Kepler Space Telescope have revealed oscillation modes with unexpectedly low amplitudes, suggesting that nonlinear wave-wave interactions may transfer energy between resonant modes. We employ analytical calculations and numerical simulations to examine nonlinear coupling in red giants, first validating the accuracy of frequencies, amplitudes, and phases recovered from finite observations using Lomb-Scargle analysis, then quantifying how observing duration affects the error in these values. We then apply these methods to stars with resonant mode triplets cataloged in the Kepler Red Giant Peak Bagging Database. To model these systems, we create simulations of stochastically-driven mode triplets with enabled and disabled nonlinear coupling. We analyze and compare these to derived analytical expressions of root mean square mode amplitudes and the ensemble averages of complex mode amplitudes. Comparisons between theory and simulations show close agreement, within approximately a factor of 100, indicating that nonlinear mode coupling may generate observable correlations among oscillation modes in red giant stars.

BS (Bachelor of Science)

asteroseismology; red giants; Kepler Space Telescope; nonlinear coupling

English

2026-05-11