On the Characteristics of the Solar Gravity Mode Frequencies

Abstract

Gravity modes are the best probes for studying the dynamics of the solar radiative zone, and especially the nuclear core. This paper shows how specific physical processes influence the theoretical g-mode frequencies for the l=1 and l=2 modes over a large range of radial orders n from -46 to -1, corresponding to potential SOHO observations. To this end, we compute different solar models, and we calculate the corresponding theoretical g-mode frequencies. These frequencies are sensitive to the physical inputs of our solar models in the high-frequency range of the oscillation power spectrum. At low frequency, we demonstrate that the periodic spacing (ΔP_l) between two g-modes with consecutive orders n and with the same angular degree l does not vary significantly from one model to the other. For all the models considered, including models based on recent solar chemical abundances, the value of the characteristic quantity P₀, the fundamental period of the g-modes, is constant within a 1 minute range (between 34 and 35 minutes). This result is in sharp contrast to the situation before the launch of the SOHO spacecraft, when the dispersion for P₀ was large (with values ranging from 29 to 60 minutes). Then, we estimate the sensitivity of the oscillation frequency splittings to the solar core rotation. Finally, we review some features of the g-mode observations obtained with the GOLF instrument and based on an almost complete solar cycle. Some of these help us constrain the excitation mechanisms of g-modes.