Equations of state for stellar partial ionization zones

Journal Article · Tue Nov 01 04:00:00 EST 1977 · Astrophys. J., Suppl. Ser.; (United States)

DOI:https://doi.org/10.1086/190482· OSTI ID:5332162

Fontaine, G; Graboske, Jr, H C; Van Horn, H M

A composite numerical equation of state has been developed to compute thermodynamic surfaces covering the density-temperature domain of interest for stellar ionization zones. Emphasis has been placed on the thermodynamic constraints of stability and consistency in obtaining the ionization equilibrium conditions for nonideal, multicomponent gases. Two different theoretical models have been used. First, in the low-denisty regime, the ionization equilibrium has been obtained by the free-energy minimization technique. This method explicitly minimizes the free energy of a statistical mechanical model by finding the equilibrium concentrations of all atomic and ionic species. This particular model includes electron degeneracy, Coulomb interactions, fluid interactions, and electronic perturbations. Second, in the high-density regime where material properties are dominated by the electron gas, a hot Thomas-Fermi model has been employed. Both these models become inaccurate in the low-temperature, intermediate-density domain, and interpolation was used to approximately describe the properties of matter in this complex region. However, by making use of Maxwell's relations, thermodynamic consistency was preserved even in this interpolation region.The results are presented in the form of extensive tables listing the pressure, the internal energy, the adiabatic gradient, and the pressure derivatives as functions of the temperature and the density. Other thermodynamic quantities of astrophysical interest such as specific heats and adiabatic exponents can easily be derived from the listed data. Different methods of composition interpolation have been investigated and it is found that an ''additive volume'' law is to be preferred. The present results are relevant to studies of pulsational properties and outer layers of white dwarfs, and also to evolutionary calculations of low-mass main-sequence stars, red giants, and white dwarfs.

• Research Organization: Departement de Physique, Universite de Montreaal
• OSTI ID: 5332162
• Journal Information: Astrophys. J., Suppl. Ser.; (United States), Journal Name: Astrophys. J., Suppl. Ser.; (United States) Vol. 35:3; ISSN APJSA
• Country of Publication: United States
• Language: English

Related Subjects

640102* -- Astrophysics & Cosmology-- Stars & Quasi-Stellar
Radio & X-Ray Sources
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ABUNDANCE
ATOMIC MODELS
CHEMICAL COMPOSITION
DWARF STARS
EQUATIONS
EQUATIONS OF STATE
EQUILIBRIUM
IONIZATION
MAIN SEQUENCE STARS
MATHEMATICAL MODELS
MECHANICS
STAR MODELS
STARS
STATISTICAL MECHANICS
THERMODYNAMICS
THOMAS-FERMI MODEL
WHITE DWARF STARS