Helioseismic inversion procedures to probe the chemical composition and thermodynamics of the sun

Before the advent of helioseismology and neutrino observations, the solar interior could only be studied through solar modeling. Since the discovery of oscillations on the solar surface, these waves, which travel deep into the solar interior, have become the tools to investigate the solar internal structure, in analogy with the way seismologists use earthquake waves to probe the internal structure of the earth. This new field was therefore adequately named helioseismology.; The main objective of the present study is the development of an inversion procedure, from which one can indirectly determine the properties of the solar internal structural. The technique is based on a differential analysis, which reveals the difference between the structure of the Sun and the structure of a solar model. Such an approach is successful, since current solar models are excellent approximations (better than 99% accuracy) of the real Sun. The structural properties examined here are the chemical composition and the equation of state. We have chosen adiabatic exponent as the probe to indicate discrepancies between the models and the Sun.; The reliability of the newly developed inversion code was tested for accuracy and stability by an extensive “model study”. Based on the experience attained from the model study, an empirical scheme has been constructed to determine the credibility of the inverted results.; In the last part, this inversion procedure has been applied to probe the unknown solar structure, more specifically, its chemical composition and the equation of state. First results show that the principal discrepancy between γ ₁ of the Sun and the current; standard solar models (e.g., Model S in Christensen-Dalsgaard et al., 1996) is likely a consequence of an incorrect assumption of the composition of heavy elements in the solar interior.