THE EFFECT OF THE MIHALAS, HUMMER, AND DAPPEN EQUATION OF STATE AND THE MOLECULAR OPACITY ON THE STANDARD SOLAR MODEL

Improvements to the Yale Rotating Stellar Evolution Code by incorporating the Mihalas-Hummer-Dappen equation of state, an improved opacity interpolation routine, and the effects of molecular opacities, calculated at Los Alamos, have been made. The effect of each of the improvements on the standard solar model has been tested independently by computing the corresponding solar nonradial oscillation frequencies. According to these tests, the Mihalas-Hummer-Dappen equation of state has very little effect on the model's low l p-mode oscillation spectrum compared to the model using the existing analytical equation of state implemented in YREC. On the other hand, the molecular opacity does improve the model's oscillation spectrum. The effect of molecular opacity on the computed solar oscillation frequencies is much larger than that of the Mihalas-Hummer-Dappen equation of state. Together, the two improvements to the physics reduce the discrepancy with observations by 10-mu-Hz for the low l modes.