Mixed modes are observed in many low-mass evolved stars. They provide information about the core rotation rates of these stars, which are lower than predicted by current stellar evolution models. The mixed modes themselves have been invoked as an angular momentum transport mechanism, but estimating their transport efficiency requires knowledge of their amplitudes. In this talk I will constrain, for the first time, the mixed mode amplitudes in 2D hydrodynamical simulations of a 1.3M⊙ red giant using the code MUSIC. I compare the modes found in two simulations, with different radial truncations ro/r⋆ = 0.90 and ro/r⋆= 0.98, with those found using both GYRE and a Dedalus eigenvalue solver. I will explore the agreement of the eigenfunctions and frequencies between simulations and linear theory, finding excellent agreement for all p-dominated modes, with minor discrepancies for most g-dominated modes. Based on an empirical scaling law the modes with largest kinetic energies are expected around νmax = 312.8 μHz, but in both simulations the modes with frequencies ν < 50 μHz are found to have the largest kinetic energies instead. Next, the simulated modes are extrapolated to the stellar surface to determine their surface velocities. Only the modes in the simulation with largest outer radial boundary ro/r⋆ = 0.98 have comparable extrapolated surface velocities to the empirical prediction, with largest surface velocities located around ν = 700 μHz. The extrapolated surface velocities of the low frequency modes are small, making them hard to observe, but their kinetic energies means they could have a large impact on angular momentum transport, which has not yet been investigated.
Revealing mixed modes in compressible hydrodynamical simulations of red giant stars
Lundi 2 mars 2026
de
11:00 à
12:00
Conference room, building 17
