Statistics – Computation
Scientific paper
Sep 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aipc.1171..242n&link_type=abstract
RECENT DIRECTIONS IN ASTROPHYSICAL QUANTITATIVE SPECTROSCOPY AND RADIATION HYDRODYNAMICS: Proceedings of the International Confe
Statistics
Computation
4
Stellar Atmospheres, Hydrodynamics, Radiative Transfer, Stellar Atmospheres, Radiative Transfer, Opacity And Line Formation, Hydrodynamics, Radiative Transfer, Scattering
Scientific paper
Stellar atmospheres provide a unique and valuable testing ground for radiation hydrodynamics and MHD. Spectral line synthesis based on reasonably affordable 3-D models can potentially reach very high accuracy, with widths, strengths, and shapes of photospheric spectral lines matching observations to within fractions of a percent, with ``no free parameters'' i.e., using only the effective temperature, surface acceleration of gravity, and element abundances as input parameters, and without the need for artificial fitting parameters such as micro- and macro-turbulence. When combined with accurate atomic parameters the results can be used to determine the abundance of individual chemical elements more accurately than was possible in the past, when spectral line synthesis was based on one-dimensional modeling and artificial fitting parameters. A necessary condition for reaching the desired accuracy is that the radiative energy transfer in the photosphere is treated with sufficient accuracy. Since at different levels in stellar atmospheres different wavelength regions dominate the energy exchange between the gas and the radiation field this is a non-trivial and potentially very computer intensive problem. We review the computationally efficient methods that are being used to achieve accurate solutions to this problem, addressing in particular the relation to the solar ``oxygen abundance problem.'' In this context we also briefly comment on ``look-alike'' radiative transfer methods such as Flux Limited Diffusion.
Nordlund A.˚Ke
Stein Robert F.
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