Energy levels of light atoms in strong magnetic fields

In this review article we provide an overview of the field of atomic structure of light atoms in strong magnetic fields. There is a very rich history of this field which dates back to the very birth of quantum mechanics. At various points in the past significant discoveries in science and technology have repeatedly served to rejuvenate interest in atomic structure in strong fields, broadly speaking, resulting in three eras in the development of this field; the historical, the classical and the modern eras. The motivations for studying atomic structure have also changed significantly as time progressed. The review presents a chronological summary of the major advances that occurred during these eras and discusses new insights and impetus gained. The review is concluded with a description of the latest findings and the future prospects for one of the most remarkably cutting-edge fields of research in science today.Comment: 37 pages, 16 figures, 1 tabl

Atmospheres and radiating surfaces of neutron stars

The early 21st century witnesses a dramatic rise in the study of thermal radiation of neutron stars. Modern space telescopes have provided a wealth of valuable information which, when properly interpreted, can elucidate the physics of superdense matter in the interior of these stars. This interpretation is necessarily based on the theory of formation of neutron star thermal spectra, which, in turn, is based on plasma physics and on the understanding of radiative processes in stellar photospheres. In this paper, the current status of the theory is reviewed with particular emphasis on neutron stars with strong magnetic fields. In addition to the conventional deep (semi-infinite) atmospheres, radiative condensed surfaces of neutron stars and "thin" (finite) atmospheres are considered.Comment: 43 pages, 13 figures, 1 table. In v.3, there are more than 50 minor corrections (typos, wording, style) and one important typo fix (the sign in Eq.(61)). In v.4, beside a few minor improvements, ionization equilibrium equation (58) is corrected. In v.5, a typo in Eq.(12) is fixe

Modelling mid-Z element atmospheres for strongly-magnetized neutron stars

We construct models for strongly-magnetized neutron star atmospheres composed of mid-Z elements (carbon, oxygen and neon) with magnetic fields B=10^{12}-10^{13} G and effective temperatures Teff=(1-5)*10^6 K; this is done by first addressing the physics relevant to strongly-magnetized plasmas and calculating the equation of state and polarization-dependent opacities. We then obtain the atmosphere structure and spectrum by solving the radiative transfer equations in hydrostatic and radiative equilibrium. In contrast to hydrogen opacities at the relevant temperatures, mid-Z element opacities are dominated by numerous bound-bound and bound-free transitions. Consequently, temperature profiles are closer to grey profiles, and photosphere densities are lower than in the hydrogen case. Mid-Z element atmosphere spectra are significantly softer than hydrogen atmosphere spectra and show numerous absorption lines and edges. The atmosphere spectra depend strongly on surface composition and magnetic field but weakly on surface gravity. Absorption lines are primarily broadened by motional Stark effects and the (unknown) surface magnetic field distribution. Given the multiple absorption features observed from several isolated neutron stars, it is possible to determine, with existing X-ray data, the surface composition, magnetic field, temperature, and gravitational redshift; we present qualitative comparisons between our model spectra and the neutron stars 1E1207.4-5209 and RX J1605.3+3249. Future high-resolution X-ray missions such as Constellation-X will measure the gravitational redshift with high accuracy by resolving narrow absorption features, and when combined with radius measurements, it will be possible to uniquely determine the mass and radius of isolated neutron stars. (Abridged)Comment: 16 pages, 22 figures, accepted for publication in MNRA

Atmospheric NLTE-models for the spectroscopic analysis of massive stars

This work aims at advancing current tools for the quantitative optical spectroscopy of O-stars, in order to derive carbon, nitrogen and oxygen abundances using an automatized method applicable also to large samples of spectra. These abundances allow us to check current predictions on massive star evolution, and to establish tighter constraints on the impact of rotational mixing and other processes. Already on the Main Sequence, massive stars might display chemical abundance variations on short time-scales, where the CNO cycle produces nitrogen at the expense of carbon and - later on - oxygen. These variations represent a key feature to evaluate the reliability of corresponding theoretical models and are one of the main topics investigated in the present thesis.Das Ziel vorliegender Dissertation ist es, geeignete Werkzeuge für die quantitative Spektroskopie von O-Sternen im optischen Spektralbereich bereitz-stellen, um deren Kohlenstoff-, Stickstoff- und Sauerstoffhäufigkeiten zu bestimmen, und zwar mittels automatisierter Methoden, die auch auf große Stichproben anwendbar sind. Solche Häufigkeiten erlauben uns dabei, Vorhersagen aktueller Sternent-wickungsmodelle massereicher Sterne zu überprüfen, und insbesondere den Einfluss von Rotations-mischung und verwandter Prozesse einzugrenzen. Bereits auf der Hauptreihe können massereiche Sterne chemische Häufigkeitsvariationen auf kurzen Zeitskalen aufweisen, wobei der CNO-Zyklus Stickstoff auf Kosten von Kohlenstoff und - später - Sauerstoff produziert. Diese Variationen stellen ein Schlüsselmerkmal dar, um die Zuverlässigkeit entsprechender theoretischer Modelle zu bewerten, und sind eines der Hauptthemen vorliegender Arbeit

Spectral Line Shapes in Plasmas

International audienceFor the first two Spectral Line Shapes in Plasma workshops, participants submitted in total over 1,500 line-shape calculations. The studies collected in this Special Issue explore only a part of this immense work. This book is a reprint of the special issue that appeared in the online open access journal Atoms (ISSN 2218-2004) in 2014 (available at: http://www.mdpi.com/journal/atoms/special_issues/SpectralLineShapes)

Transport methods and interactions for space radiations

A review of the program in space radiation protection at the Langley Research Center is given. The relevant Boltzmann equations are given with a discussion of approximation procedures for space applications. The interaction coefficients are related to solution of the many-body Schroedinger equation with nuclear and electromagnetic forces. Various solution techniques are discussed to obtain relevant interaction cross sections with extensive comparison with experiments. Solution techniques for the Boltzmann equations are discussed in detail. Transport computer code validation is discussed through analytical benchmarking, comparison with other codes, comparison with laboratory experiments and measurements in space. Applications to lunar and Mars missions are discussed

Branch-point structure and energy level calculations of diamagnetic hydrogen using dimensional perturbation theory.

This dissertation describes the results of research that covers two distinct areas relevant to the field of physics: atomic theory and applied numerical analysis. In the first phase of this research the avoided crossings of diamagnetic hydrogen were examined with dimensional perturbation theory, resulting in a systematic means of understanding the appearance of these avoided crossings and where they will occur in the energy spectrum. In the second phase of this research we turned our attention to the field of approximation theory, developing a more accurate technique for summing divergent perturbation series at specific values of the independent variable. The two phases of research were finally related by applying this new technique to the diamagnetic hydrogen problem, with improved convergence and accuracy when summing the perturbation energy series