Effects of Opacity and Equation of State on Solar Structure and Oscillations

The evolution and p-mode oscillation frequencies of several solar models are presented, highlighting the effects of uncertainties in the opacity and equation of state. The Dappen, Mihalas, Hummer, and Mihalas ('MHD') equation of state tables are incorporated into the evolution and oscillation calculations, and the results are compared with those of models calculated using the analytical Iben equation of state. The nonadiabatic low-degree p-mode oscillation frequencies derived from models using either of these equations of state agree with observations to within a few microhertz. The MHD equation of state, with more detailed treatment of envelope ionization regions, improves agreement with observations for p-modes of degree l = 40-300. For higher degree p-modes, observational uncertainties make it difficult to determine how much improvement the MHD equation of state provides over the analytical Iben procedure. Calculated p-mode oscillation frequencies favor the higher Ross-Aller opacities, which include molecular effects and more iron lines, over the older Cox-Tabor opacities in the solar envelope at temperatures below 9000 K. Thus, solar oscillations can be effectively used to constrain opacities at the solar surface and below the convection zone. 32 refs.