On the excitation of oscillations of the Sun (numerical models)

Numerical solutions of the general time-dependent gas-dynamical equations in linear adiabatic approximation are given for initial conditions imitating: (a) a central perturbation, (b) a boundary perturbation (in the convective envelope), and (c) a 'shrinking' of the Sun as a whole. For a variety of models of the Sun it is found that at the surface the radial component v_r of velocity is much greater than the tangential component v_t, and that the period T of stationary oscillations does not exceed 131^m. The appearance at the surface of a g mode with period 160^m is found to be improbable. With the initial conditions adopted, a propagating wave is produced which is reflected successively from the centre to the periphery and back, producing 5-min oscillations at the surface of the Sun. Expansion of this wave into separate modes leads to a power spectrum qualitatively similar to that observed.