AAS Meeting #193 - Austin, Texas, January 1999
Session 98. Low Mass Stars and Brown Dwarfs
Display, Saturday, January 9, 1999, 9:20am-4:00pm, Exhibit Hall 1

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[98.01] OPAL Equation of State for Low Mass Stars

F. J. Rogers (LLNL), A. Nayfonov (Univ.Southern California and IGPP, LLNL)

We have used an activity expansion method, based on a many-body expansion of the grand canonical partition function, to calculate the equation of state of steller material. The method considers from the outset electrons and nuclei, so that plasma effects on bound states arises naturally from the theory. The activity expansion method avoids many of the ad-hoc approximations used in the usual free energy minimization approaches. Rogers, Swenson and Iglesias (1996, ApJ, 456) used an earlier version of this work to calculate the equation of state tables for stars having mass greater than 0.8 M0. In the present work we have extended the OPAL tables to include stars with masses greater than 0.3 M0. We now include relativity in the free electron degeneracy and exchange terms. We also use better estimates for the molecular partition functions and the effects of molecular interaction.

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The author(s) of this abstract have provided an email address for comments about the abstract: rogers4@llnl.gov

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