Surface-effect corrections for the solar model

Abstract

Solar p-mode oscillations exhibit a systematic offset towards higher frequencies due to shortcomings in the 1D stellar structure models, especially, the lack of turbulent pressure in the superadiabatic layers just below the optical surface, arising from the convective velocity field. We study the influence of the turbulent expansion, chemical composition, and magnetic fields on the stratification in the upper layers of the solar models in comparison with solar observations. Furthermore, we test alternative <3D> averages for improved results on the oscillation frequencies. We appended temporally and spatially averaged <3D> stratifications to 1D models to compute adiabatic oscillation frequencies that we then tested against observations. We also developed depth-dependent corrections for the solar 1D model, for which we expanded the geometrical depth to match the pressure stratification of the solar <3D> model, and we reduced the density that is caused by the turbulent pressure. We obtain the same results with our <3D> models as have been reported previously. Our depth-dependent corrected 1D models match the observations to almost a similar extent as the <3D> model. We find that correcting for the expansion of the geometrical depth and the reducing of the density are both equally necessary. Interestingly, the influence of the adiabatic exponent Gam1 is less pronounced than anticipated. The turbulent elevation directly from the <3D> model does not match the observations properly. Considering different reference depth scales for the <3D> averaging leads to very similar frequencies. Solar models with high metal abundances in their initial chemical composition match the low-frequency part much better. We find a linear relation between the p-mode frequency shift and the vertical magnetic field strength with dvnl = 26.21Bz microHz/kG, which is able to render the solar activity cycles correctly.

10 pages, 14 figures, accepted for publication in A&A

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