On density and temperature-dependent ground-state and continuum effects in the equation of state for stellar interiors -- A Comment on the paper by S. Arndt, W. Dappen and A. Nayfonov 1998, ApJ 498, 349

Misunderstandings have occurred regarding the conclusions of the paper by S. Arndt, W. Dappen and A. Nayfonov 1998, ApJ 498, 349. At occasions, its results were interpreted as if it had shown basic flaws in the general theory of dynamical screening. The aim of this comment is to emphasize in which connection the conclusions of the paper have to be understood in order to avoid misinterpretations.Comment: Astrophysical Journal (to appear 1 May 1999), 5 page

The Signature of the Internal Partition Function in Thermodynamical Quantities of the Solar Interior

The extraordinary accuracy of available helioseismological data presents an opportunity to study nonideal plasma effects of the solar interior beyond the leading-order Coulomb correction term. The effect of different internal partition functions on a complete set of thermodynamical quantities is examined and it is found that there is a clear signature of the excited states well within reach of present helioseismic inversion techniques. Subject headings: stellar interior, helioseismology, equation of state, thermodynamic quantities, partition function, excited states -- 3 -- 1. Introduction The equation of state is one of the three fundamental ingredients used to construct stellar models (Christensen-Dalsgaard et al. 1996). The other two are opacity and nuclear energy reaction rates. One star - the Sun - is very special in two respects. First, the methods of helioseismology allow us to obtain very accurate experimental data of the solar interior (in particular, sound speed and density..

On Density and Temperature-Dependent Ground-State and Continuum Effects in the Equation of State for Stellar Interiors

The consequence of shifts in bound-state energies and the position of the continuum for thermodynamic quantities are examined. Two independent methods from different branches of physics are brought together. A simple free-energy model is used to examine the thermodynamic consequences of the results of a quantum statistical calculations of two-particle properties in a plasma using Green-function technique. A comparison with data inferred from helioseismology shows that our interdisciplinary procedure works very well for lower-level approximations, such as the static screening in the effective two-particle wave equation. However, in the case of dynamic screening in the wave equation, the resulting thermodynamic quantities are inconsistent with observations. This could be due to an inadequacy of our method to compute the thermodynamic quantities, or due to an inappropriate treatment of the ion contribution to the electronic self energy corresponding to the dielectric function used in rand..