Stellar acoustic mode

A stellar acoustic mode is a pressure-restored stellar oscillation. Its local high-frequency propagation branch lies above the stellar buoyancy frequency and Lamb frequency. Inner refraction and near-surface reflection form an acoustic cavity; its standing-wave frequencies probe the adiabatic sound speed profile.

The leading separation between successive high-order low-degree stellar acoustic mode frequencies is the inverse round-trip acoustic travel time, $\Delta \nu \simeq [2{\int }_0^{R}dr/c_s{]}^{-1}$. For homologous stars it scales approximately as $(M/R^3{)}^{1/2}$ and therefore measures mean density.