Starting from the free-energy minimization method in the chemical picture, we have derived analytical and simplified expressions for the physical processes of Coulomb coupling, pressure ionization and electron degeneracy. Thus, we are able to establish a single algorithm of equation of state involving a sum of terms, each including a different physical contribution. This makes it possible to incorporate nonideal effects into the stellar evolution codes with direct call of EOS. Therefore, the thermodynamic quantities of the plasma may be calculated explicitly and very quickly over a wide range of temperature and density.
The purpose of this paper is to examine the nonideal effects on the EOS for solar interior matter. We have found that the corrections have a significant effect on the solar equation of state. In addition, our simple and comprehensive algorithm also allows us to incorporate more physical processes or add more elements into the EOS. Although our improved formulation of the equation of state can be of benefit to the study of the complexity of physical processes concerned in the EOS, the influence of the nonideality on the EOS as shown in this paper remains approximate. More studies would be needed to fully understand finer infulence of nonideality on the equation of state.
© European Southern Observatory (ESO) 2000
Online publication: January 29, 2001