Seismic inversions for temperature and chemical composition profiles in the solar interior

Abstract

The primary inversion of the accurately measured frequencies of solar oscillations determines the mechanical properties of the Sun, i.e., the sound speed and density as a function of solar radius. In order to infer the temperature and hydrogen abundance profiles inside the Sun, it becomes necessary to use, in addition, the equations of thermal equilibrium along with the input physics, such as opacities, equation of state and nuclear reaction rates. It then becomes possible to estimate the effects of uncertainties in opacity and nuclear reaction rates on the inferred thermal and composition profiles. The seismically determined temperature and hydrogen abundance profiles turn out to be close to those in a standard evolutionary solar model that includes the diffusion of helium and heavy elements below the convection zone. The most significant departure occurs just below the base of the convection zone where the inferred hydrogen abundance profile is smoother than that in a standard diffusion model. The region just beneath the solar convection zone appears to be mixed, a process which could account for the observed low lithium abundance in the solar envelope. With a reasonable allowance for errors in opacities, the helioseismically estimated cross-section for pp nuclear reaction rate turns out to be (4.15+/-0.25)*1.E-25 MeV barns.