Effects of Heavy Elements and Excited States in the Equation of State of the Solar Interior

Although 98% of the solar material consists of hydrogen and helium, theremaining chemical elements contribute in a discernible way to thethermodynamic quantities. The contribution of various heavy elements in a setof thermodynamic quantities has been examined. It has emerged that prominentsignatures of individual elements exist, and that these effects are greatest inthe ionization zones, typically located near the bottom of the convection zone.The main result is that part of the features found here depend strongly both onthe given species (atom or ion) and its detailed internal partition function,whereas other features only depend on the presence of the species itself, noton details such as the internal partition function. The latter features areobviously well suited for a helioseismic abundance determination, while theformer features present a unique opportunity to use the sun as a laboratory totest the validity of physical theories of partial ionization in a relativelydense and hot plasma. This domain of plasma physics has so far no competitionfrom terrestrial laboratories. [shortened version of original abstract]Comment: Accepted for publication in ApJ (to appear December 2001); 40 pages, 17 figure