2D calculations for atoms and ions in strong magnetic fields of white dwarfs and neutron stars

The following work is devoted to the description of atoms and ions in strong magnetic fields as they can occur in the vicinity of magnetic white dwarfs and neutron stars. The ultimate goal of this work is the contribution to an understanding of unique absorption features detected in the spectra of such stars. One natural explanation for these features are atomic absorptions in the stars’ strongly magnetized atmospheres. Models for the atmospheres of magnetic white dwarfs and corresponding spectra have already been applied with great success to observed data, and absorption features of the light elements hydrogen and helium were identified. A comparable success in the modeling of neutron star atmospheres has still to be accomplished. This is related to the extreme conditions in neutron star atmospheres, namely very high temperatures, magnetic fields, and particle densities. Also, the progenitors of neutron stars produce heavy elements up to iron, which are likely to contribute to the composition of the neutron star atmosphere. The poor knowledge of atomic data of heavier elements in strong magnetic fields hampers the further understanding of neutron star emission spectra. In this work we present reliable and fast programs that are capable of creating a large database for atomic states and transitions in a wide range of the magnetic field strength. Based upon previous work we implemented a two-dimensional Hartree-Fock-Roothaan method that overcomes former restrictions, namely the adiabatic approximation and the Landau orbital product ansatz. This software suite allows for a precise description of atomic wave functions and energy values in an extended range of magnetic field strengths. Additionally, the programs are capable of calculating atomic transition energies and strengths. During the development of these programs we focused on automated data production and processing, and payed special attention to program reliability and execution speed. The results for the hydrogen atom presented in this work have already proven useful in the context of an astrophysical application, and improve current atmosphere model calculations of magnetic white dwarfs. Further, our results enhance the understanding of atomic energy spectra at neutron star magnetic fields. The wave functions and energy values calculated in this thesis serve as a starting point for other methods, e.g. the fixed-phase diffusion quantum Monte Carlo method, as well as for photoionization calculations of atoms in strong magnetic fields.