Astron. Astrophys. 326, 187-194 (1997)

Solar models: influence of equation of state and opacity

M. Yldz ¹ and N. Kzloglu <sup>2

1</sup> Ege University, Department of Astronomy and Space Sciences, Izmir 35100 , Turkey
² Middle East Technical University, Physics Department, Ankara 06531, Turkey

Received 18 September 1996 / Accepted 23 April 1997

Abstract

Solar models through evolutionary phases of gravitational contraction, pre-main sequence and MS phases, up to current age and , were studied adopting different prescriptions for the equation of state (EOS) and different opacity tables.

Old EOS in Ezer's evolutionary code that we adopted in previous studies includes pressure ionization, and degeneracy of electrons. In the present study the EOS is obtained by minimization of the free energy (Mihalas et al. 1990, MHD), and the radiative opacity is derived from recent OPAL tables, implemented by the low temperature tables of Alexander & Ferguson. The results are compared with solar models we computed with different radiative opacities (Cox & Stewart 1970) and different EOS, as with models computed by other authors.

Finally we provide the internal run of the thermodynamic quantities of our preferred solar model which possesses the following characteristics: age , initial He abundance by mass 0.285, parameter of the mixing length , radius and temperature at the bottom of the convective envelope are and , respectively.

Key words: Sun: interior solar evolution equation of state

Send offprint requests to: M. Yldz

Contents

• 1. Introduction
• 2. Basics of the modeling
• 3. Input physics
  • 3.1. Opacity
  • 3.2. Equation of state: minimization of free energy
    • 3.2.1. Degeneracy of electrons
    • 3.2.2. Boltzmann gas and partition function
    • 3.2.3. Coulomb interaction
    • 3.2.4. Saha equation
  • 3.3. Computational method of EOS
• 4. Influence of MHD EOS
• 5. Results and discussion
• Acknowledgements
• References

© European Southern Observatory (ESO) 1997

Online publication: April 20, 1998
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