W. Däppen, D. Mao
May 8, 2009
Journal of Physics A: Mathematical and Theoretical
The modulation of the equation of state by the chemical composition leads to a natural method to determine the helium and heavy-element abundance in the sun and stars. For solar helium this has indeed become the only reliable method. However, one has to keep in mind that the result is only as good as the quality of the equation of state. So far, there are only theoretical formalisms, but no experiments, for the relevant physical conditions. It is obvious that sharp theoretical tools in the form of smooth thermodynamic (and opacity) quantities are crucial for the interpretation of the astrophysical data, both for abundance determinations and improvements of the theory. An emulator of the OPAL equation of state was developed, by which the OPAL equation of state can be applied directly in stellar models, without recourse to pre-computed tables.