Seismology of the solar convection zone
M. J. P. F. G. Monteiro
The thesis deals with the study of several problems associated with the solar convective envelope using seismic data. We start with a general introduction to the subject of solar seismology and convection with the basic physics being presented in the appendices. A general discussion on the seismic properties of solar models including asymptotic analysis are also reviewed having in mind their later use.
The detection of convective overshoot at the base of the solar convection zone is the first topic to be presented, starting with a discussion of the theoretically expected behaviour of the oscillations in the presence of overshooting. Using a variational principle for linear adiabatic nonradial oscillations an expression for the frequency changes due to overshoot at the base of the convection zone, modelled as predicted by several studies, is deduced. We then proceed to a detailed application to solar models. The implications of the assumptions present in the analysis are determined and their effect on the conclusions established. Finally, solar data are used to determine the extent and properties of the solar overshoot region using the calibration constructed with the solar models.
We then proceed to another application of the method developed in connection with overshoot, by investigating the possibility of determining the solar helium abundance. This is done by using the effect of the second ionization of helium in the solar structure and frequencies of oscillation. The main advantages and limitations of this method are investigated.
A qualitative and quantitative study of the importance of how we model low-efficiency convection on the seismic properties of a solar model is also discussed. We introduce a general parametrization that has as particular cases the standard mixing length theory and other recently proposed corrections to this description. Using such a parametrization it is shown how significant can be the shift in absolute value of the frequencies due to this extremely thin region at the top of the solar convective envelope. We then proceed to analyse why this is so and attempt to constrain the available theoretical descriptions of convective energy transport in the solar envelope. Other effects associated with convection and also contributing to the discrepancy in the observed frequencies are also reviewed. We analyse some of these using numerical simulations of convection.
The main results of the above topics are reviewed and discussed with the suggestion of some possible implications to be considered in future in the concluding Chapter of the thesis. Also included in the thesis are two appendices which review the basics physics and mathematics involved both in calculating solar models and their frequencies of oscillation.
Doutoramento em Astronomia (Reino Unido)