THE P-MODE OSCILLATION SPECTRA OF AN EVOLVING 1-M. SUN-LIKE STAR

The p-mode frequencies, the first-order spacings [v(n, l) - v(n - 1, l + 2)] of a 1 M. star, with solar composition, have been calculated for six models ranging from the zero-age main sequence to the base of the giant branch. The behavior of the frequency spacings, as a function of frequency and age, are analyzed in terms of the structure of the models. The calculated frequency spacings, when compared to observations of solar oscillations, reveal the Sun's deep interior to have the structure of a younger than 4.89 Gyr old stellar model (i.e., less concentrated than predicted by a standard stellar model), and the Sun's middle regions to have the structure of an older than 4.89 Gyr old stellar model (i.e., more concentrated than predicted by a standard stellar model). This structure is consistent with nonstandard modeling schemes proposed to reduce the predicted solar neutrino flux. For the most evolved models, near the base of the giant branch, mixed modes (modes with g-mode-like oscillations in the interior and p-mode-like oscillations in the outer layers) occur and disrupt the near-constancy of the frequency spacings. This is discussed. In addition, the small amplitude periodic variations in frequency of the first-order spacings of the Sun's p modes within the context of the possible existence of a discontinuity in density stratification located in the outer envelope of the Sun are briefly described.