Strong Magnetic Field Effects and Molecular Processes with Applications to White Dwarfs

Radiative transitions of hydrogenlike atoms in external magnetic fields of strength applicable to magnetic white dwarfs, i.e. B \u3c 103 megagauss, have been investigated for field-free principal quantum numbers n \u3c 6. Finite proton mass corrections are included. Relativistic corrections are also investigated. Transition probabilities are determined using the length, velocity, and acceleration forms of the electric dipole operator. Discrepancies between previous calculations and magnetic white dwarf observations of low-lying boundbound transitions have been studied. New results for high-lying transitions are also obtained. The transition probability for the hydrogenlike 2s two-photon decay has been investigated and shown to increase substantially with field strength. The computed two-photon spectra show resonances and interference minima. Anomalous Zeeman depolarization features are found in computed two-photon polarization spectra of alkali atoms in laboratory strength magnetic fields. A previously observed fine structure depolarization feature is shown to decay with decreasing field strength

Cosmological Recombination of Lithium and its Effect on the Microwave Background Anisotropies

The cosmological recombination history of lithium, produced during Big--Bang nucleosynthesis, is presented using updated chemistry and cosmological parameters consistent with recent cosmic microwave background (CMB) measurements. For the popular set of cosmological parameters, about a fifth of the lithium ions recombine into neutral atoms by a redshift $z\sim 400$. The neutral lithium atoms scatter resonantly the CMB at 6708 \AA and distort its intensity and polarization anisotropies at observed wavelengths around $\sim 300 \mu$m, as originally suggested by Loeb (2001). The modified anistropies resulting from the lithium recombination history are calculated for a variety of cosmological models and found to result primarily in a suppression of the power spectrum amplitude. Significant modification of the power spectrum occurs for models which assume a large primordial abundance of lithium. While detection of the lithium signal might prove difficult, if offers the possibility of inferring the lithium primordial abundance and is the only probe proposed to date of the large-scale structure of the Universe for $z\sim 500-100$.Comment: 20 pages, 7 figure

Molecular properties of polymeric materials for space applications

This cooperative agreement was intended to investigate the effects of a space environment on the properties of polymeric materials. In addition, efforts have been made to understand and investigate environment simulation techniques and test methodology. The results identified the changes in the properties of six aerospace structural adhesives, three neat high polymers, and two fiber-reinforced polymers, as caused by exposure to four simulated space environmental conditions. Significant property changes occurred for several of the systems as a result of one or more of the exposures. A summary of the research follows a list of related publications and presentations

Advances in Atomic Data for Neutron-Capture Elements

Neutron(n)-capture elements (atomic number Z>30), which can be produced in planetary nebula (PN) progenitor stars via s-process nucleosynthesis, have been detected in nearly 100 PNe. This demonstrates that nebular spectroscopy is a potentially powerful tool for studying the production and chemical evolution of trans-iron elements. However, significant challenges must be addressed before this goal can be achieved. One of the most substantial hurdles is the lack of atomic data for n-capture elements, particularly that needed to solve for their ionization equilibrium (and hence to convert ionic abundances to elemental abundances). To address this need, we have computed photoionization cross sections and radiative and dielectronic recombination rate coefficients for the first six ions of Se and Kr. The calculations were benchmarked against experimental photoionization cross section measurements. In addition, we computed charge transfer (CT) rate coefficients for ions of six n-capture elements. These efforts will enable the accurate determination of nebular Se and Kr abundances, allowing robust investigations of s-process enrichments in PNe.Comment: To be published in IAU Symp. 283: Planetary Nebulae, an Eye to the Future; 2 page