Sensitivity of Solar Oscillation Frequencies to Element Abundances

Abstract

We are fortunate to live close enough to a pulsating star, the sun, for which we can resolve the disk and thereby measure the frequencies of thousands of its global modes of oscillation. These nonradial p-modes travel to varying depths in the solar interior, and their frequencies have been measured in some cases to a precision of one part in a million; therefore they are extremely sensitive probes of solar interior structure. The process of using solar oscillations to determine the solar interior structure and test the physical input to solar models is called “helioseismology”, analogous to the way that seismic waves are used to infer the Earth’s interior structure. The modern standard solar model generally has been successful in reproducing observed frequencies and the inferred sound speed of the solar interior. Nevertheless, discrepancies of several tenths of a percent in sound speed persist-these small differences are used as clues to refine the model assumptions and input physics. In this review we discuss the degree to which helioseismology is sensitive to element abundances and composition gradients in the solar interior.