Impact of rotation on the amplitude of acoustic modes in solar-like stars: Insights from hydrodynamical simulations

TL;DR

The study addresses why many solar-like stars show no detectable acoustic modes, especially rapid rotators, by testing the theory that rotation suppresses stochastic excitation of p modes. It employs fully compressible, global 2.5D hydrodynamical simulations with the MUSIC code for a $1\,M_{\odot}$ solar-like model at five rotation rates $\\Omega = 0,1,3,5,8\,\\Omega_{\\odot}$ to quantify changes in p-mode amplitudes and damping. Results show a systematic decline in p-mode amplitudes with increasing rotation (about 21–77% reductions) and a tendency for damping to rise at high rotation; the injected power inferred from simulations generally matches theoretical expectations based on a Lorentzian eddy-time correlation, with larger discrepancies at the fastest rate possibly due to differential rotation effects. These findings demonstrate that rotation significantly modifies oscillation properties and must be accounted for in interpreting asteroseismic data, with implications for upcoming PLATO observations and future 3D/magnetohydrodynamic extensions.

Abstract

In solar-like stars, acoustic modes provide the main way of probing their internal structure and dynamics. Although these modes are expected to be ubiquitous in stars with convective envelopes, Kepler observations reveal that a significant fraction of solar-like stars show no detectable acoustic modes, particularly among rapidly rotating and magnetically active stars. Recent theoretical work by Bessila et al. (2025) has proposed that rotation tends to inhibit convective motions, thereby reducing the power available for stochastic mode excitation. Here, we test this prediction using fully compressible hydrodynamical simulations of a solar-like star. We perform a series of 2.5D simulations, which consider longitudinal symmetry, using the MUSIC code spanning rotation rates from 0 to 8 $Ω_{\odot}$. We find a clear and systematic decline of acoustic mode amplitudes with increasing rotation rate. In the most rapidly rotating models, mode damping rates are also enhanced. The combined reduction in excitation and increase in damping with increasing rotation rate provide a physical explanation for the observed decrease in mode detectability in rapidly rotating solar-like stars. Our results demonstrate that rotation can significantly modify oscillation properties and must be accounted for when interpreting asteroseismic observations.

Figures (11)

• Figure 1: Snapshots of the instantaneous radial velocity in the five simulations, normalised by its root-mean-square value. Red indicates outward and blue inward motions.
• Figure 2: Comparison of the power spectra of the radial velocity measured in the simulations at $r=0.9 R_{\rm star}$ for angular degrees $\ell$ between 0 and 5 (top left panel). We also show the eigenfrequencies of the 1D model predicted by GYRE (vertical blue dashed lines) and the Lamb frequencies (vertical dotted black lines). The ratio of the $p$ modes' amplitudes in a rotating simulation to the non-rotating case for $\ell \in [0;5]$ (bottom left), $\ell = 0$ (top right) and $\ell = 1$ (bottom right) as a function of frequency for 5 different rotation rates. The horizontal lines represent the amplitude ratios averaged over all modes of a given simulation.
• Figure 3: Variation with the rotation rate of the ratio of $p$ modes' amplitude $P$ measured in rotating simulations to the amplitude in the non-rotating simulation $P_0$ (plain blue curves), and of the ratio of the power injected into the modes in the rotating to the non-rotating case, predicted theoretically (orange curve) and measured in simulations (dashed blue curve).
• Figure 4: Measurement of the half linewidth $\Gamma$ of the $p$ mode $\ell = 4$ and $\nu = 2.243$ mHz. The upper plot shows the power spectra $P[\hat{\rm v}_r^2]$ computed using the radial velocity in each simulation, and the lower plot shows the normalised power spectrum $P_{\rm norm}[\hat{\rm v}_r^2]$ (plain curves) and the Lorentzian fit (dotted lines).
• Figure 5: Root-mean-square velocity computed using the radial velocity component. The inset is a zoom around the convective region.