Statistics – Applications
Scientific paper
Oct 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004phdt.........6t&link_type=abstract
Thesis (PhD). MICHIGAN STATE UNIVERSITY, Source DAI-B 65/04, p. 1911, Oct 2004, 209 pages.
Statistics
Applications
2
Scientific paper
I present the ingredients for high precision, 3D hydrodynamical simulations of convection in stellar atmospheres, as well as a number of applications. I have developed a new scheme for evaluating radiative transfer, an improved equation of state and I have investigated a number of directions for improving the numerical stability of the convection simulations. The equation of state (EOS) used for the simulations, is updated by including post-Holtsmark micro-field distributions and relativistic electron-degeneracy as previously published. I have further included quantum effects, higher-order Coulomb interactions and improved treatment of extended particles. These processes (except relativistic degeneracy) have a significant effect in the solar convection zone, and most of them peak at a depth of only 10 Mm. I also include a range of astrophysically significant molecules, besides H2 and the H+2 -ion. This FOS will be used directly in the convection simulations, providing the thermodynamic state of the plasma, and as a foundation for a new calculation of opacities for stellar atmospheres and interiors. A new scheme for evaluating radiative transfer in dynamic and multi-dimensional stellar atmosphere calculations is developed. The idea being, that if carefully chosen, very few wavelengths can reproduce the full radiative transfer solution. This method is based on a calibration against a full solution to a 1D reference atmosphere, and is therefore not relevant for static 1D stellar atmosphere modeling. The first tests of the method are very promising, and reveal that the new method is an improvement over the former opacity binning technique. The range of convective fluctuations is spanned more accurately and not only the radiative heating, but also the first three angular moments of the specific intensity, can be evaluated reliably. Work on implementing the method in the convection-code, is in progress. These developments will be employed in the future for a number of detailed simulations of primary targets for the upcoming, space-based, astero-seismology missions, and will include a Cen A and B, η Boo. Procyon and β Hyi. Work on a 10 Mm deep solar simulation was severely hampered by numerical instabilities, but investigating the issue has revealed a number of potential solutions that will be tested in the near future. The work on individual stars will soon be superseded by an effort to compute a grid of convection simulations in Teff, log g and metallicity, [Fe/H], in the spirit of present-day, grids of conventional atmosphere models.
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