AN ASYMPTOTIC DESCRIPTION OF SOLAR ACOUSTIC-OSCILLATIONS WITH AN ELEMENTARY EXCITATION SOURCE

We extend the asymptotic description of solar p-modes to include an excitation source. The linear dynamic response of a star is considered within the general framework of a Fourier transform of the source function in time, and a vector spherical harmonic decomposition in space. Quantitative analysis is developed for the linear response to an 'elementary' harmonic excitation source described by a delta-function in the radial direction, using a simplified description of the energy leakage from the acoustic cavity. The synthetic p-mode power spectra are computed numerically for different depths of the excitation source, and their simple properties are discussed. The asymptotic eigenfrequency equation is generalized to describe the frequencies of maximum amplitudes in the theoretical response function. The resulting frequency equation with modified 'surface phase shift' degenerates into the standard eigen-frequency equation at low frequencies, and describes the high-frequency 'pseudomodes' in the high-frequency limit, joining both these well-known theoretical descriptions in the intermediate frequency range.