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**Session 122 - The Sun.**

*Oral session, Thursday, January 18*

*Salon del Rey South, Hilton*

## [122.02] The Last Few Microhertz: Eliminating Remaining Discrepancies Between Observed and Calculated Solar Oscillation Frequencies

*J. A. Guzik, A. N. Cox, F. J. Swenson (Los Alamos National Laboratory)*

Because of the high observational accuracy of thousands of solar p-mode
oscillation frequencies, comparisons between observed and calculated
frequencies are an excellent means of testing solar interior physics. We
compare observed and calculated nonadiabatic oscillation frequencies of
standard solar models that include: (i) both helium and heavier element
diffusion; (ii) the latest OPAL opacity tables and Alexander amp; Ferguson
(1994) low-temperature opacities; and (iii) either the MHD (Mihalas et al.
1988) or OPAL (Rogers, Swenson, amp; Iglesias 1995) equation of state. We
have already used such comparisons to determine the radius of the
convection zone base (0.712\pm 0.001 R_ødot), to determine the
envelope helium abundance (Y\sim 0.24, which validates our helium
diffusion estimates), and to rule out early mass loss and turbulent mixing
below the convection zone as solutions to the solar lithium depletion
problem.

The observed and calculated nonadiabatic frequencies of our
models agree to within a few microhertz out of 2000, but there is a
systematic decrease in the observed minus calculated frequencies with
increasing frequency. We can remove most of this residual by modifying the
structure of the model superadiabatic layers at temperatures less than
12,000 K, either by increasing the low-temperature opacities or by
alternative convection treatments. Remaining residuals for high-degree
(\ell >100) modes are reduced by including turbulent pressure, and the OPAL
EOS. Residuals for high-frequency modes (>3600 \muHz) can be reduced by
incorporating a nonequilibrium diffusion treatment in the frequency
calculations.

**Program
listing for Thursday**