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Astron. Astrophys. 364, 879-886 (2000)

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An improved equation of state under solar interior conditions

S.L. Bi 1,2, M.P. Di Mauro 2 and J. Christensen-Dalsgaard 2,3

1 Chinese Academy of Sciences, Yunnan Astronomical Observatory, NAOCAS, Kunming 650011, P.R. China (wbyw@public.km.yn.cn)
2 Theoretical Astrophysics Center, Danish National Research Foundation
3 University of Aarhus, Institute of Physics and Astronomy, 8000 Aarhus C, Denmark

Received 28 July 2000 / Accepted 31 August 2000


This paper presents a simple and efficient equation of state which can be used for quick and accurate computing of the thermodynamic functions of partly ionized and weakly coupled plasmas. Based on the free energy minimization method, the improvement of the equation of state includes a detailed account of the physical processes of non-ideal effects consisting of electron degeneracy, Coulomb coupling and pressure ionization. The treatment of Coulomb coupling combines the results of the quantum exchange effect of degenerate electrons at finite temperature, N-body semi-analytic theory and the extended Debye-Hückel theory with hard-sphere correction. For the complicated physical processes of pressure ionization an approximate model is adopted. The nonideal corrections to equation of state are calculated under solar interior conditions.

Key words: equation of state – Sun: interior – stars: interiors

Send offprint requests to: Bi Shao-Lan at Kunming address

© European Southern Observatory (ESO) 2000

Online publication: January 29, 2001