Stellar Atmospheres: Beyond Classical Models

The theory of stellar atmospheres is one of the most important branches of modern astrophysics. It is first of all a major tool for understanding all aspects of stars. As the physical properties of their outer layers can now be found with high precision, firm conclusions can be drawn about the internal structure and evolution of stars. Moreover, improvements in our knowledge of the chemical composition of stars is shedding new light on the chemical evolution of galaxies and of the Universe as a whole. Because the outer layers of stars are among the best-understood astrophysical objects, the theory of stellar atmospheres plays an important role in the study of many other types of objects. These include planetary nebulae, H II regions, interstellar matter, and objects of interest in high-energy astrophysics, such as accretion disks (close binaries, dwarf novae, cataclysmic variables, quasars, active galactic nuclei), pulsar magnetospheres, and Seyfert galaxies. Finally, as stars provide a laboratory in which plasmas can be studied under more extreme conditions than on earth, the study of stellar atmospheres has strong connections with modern physics. Astronomical observations provided a vital stimulus in the early stages of quantum theory and atomic physics; even today topics such as low-temperature dielectronic recombination develop hand in hand with the interpretation of stellar and nebular spectra. Early work on MHD was similiarly motivated. Many such connections remain to be explored.

Inhalt

Section 1..- Recent Advances in Computational Methods.- Acceleration of Convergence.- Fast Solution of Radiative Transfer Problems with a Multi-Grid Method.- Line Blanketing without LTE: Simple and Complex Spectra.- Global and Local Methods for 1-D Problems; Implementation Aspects and CPU-Time and Memory Scalings.- 2-D Axisymmetric Line Transport.- NLTE Spectral Line Formation in Three Dimensions.- Iteration with Approximate Lambda Operators, and its Application to the Expanding Atmospheres of WR Stars.- Analytical Methods of Line Formation Theory: Are They Still Alive?.- Iteration Factors in the Solution of the NLTE Line Transfer Problem.- Analysis of Ultraviolet P Cygni Profiles in the Spectra of O-Type Stars.- Computer Codes for Stellar Atmospheric Modeling.- Section 2..- The Quest for Physical Realism in Stellar Atmospheric Modeling.- Unified NLTE Model Atmospheres Including Spherical Extension and Stellar Winds: Euv-Fluxes and the HE II Discrepancy in Central Stars of Planetary Nebulae.- Non-LTE Model Atmosphere Calculations with Approximate Lambda Operators.- NLTE Model Atmospheres for Hot Stars.- Radiative Transfer in Expanding Atmospheres - Radiative Acceleration of Wolf-Rayet Envelopes?.- Non-LTE Analysis of Hot Stars Including Line Blanketing.- Time-Dependent Two-Dimensional Radiation Hydrodynamics of Accreting Matter onto Highly Magnetized Neutron Stars: The Evolution of Photon Bubbles.- The Origin and Development of Instabilities in Radiatively- Driven Stellar Winds.- A Smooth Source Function Method for Including Scattering in Radiatively Driven Wind Simulations.- 2-D Radiation Hydrodynamics Models of the Solar Photosphere.- Dynamics of and Radiative Transfer in Inhomogeneous Media.- Atmospheres of Late-Type Giants.- Fe II Emission Line Diagnostics of the Sun and Stars.- Chromospheric Inhomogeneities in Cool Stars: Possible Effect on Hydrogen Line Profiles.- Numerical Simulation of Photospheric Convection: Hydrodynamical Test Calculations.- Section 3..- Stellar Atmosphere Theory as a Spectroscopic Tool. The Example of Hot Stars.- The Winds of O-Stars. V: Tests of the Accuracy of the Radiation Driven Wind Models.- Diagnostics of Wolf-Rayet Atmospheres.- Central Stars of PN: Spectral Diagnostics Based on Model Atmospheres VS. Diagnostics Based on the Classical Nebular Approach.- Spectral Diagnostics of Hot Subdwarfs: Successes and Problems.- Temperatures, Gravities and Abundances of B Stars: Recent Progress and Remaining Problems.- Line Blanketing Without LTE: The Effect on Diagnostics for B-Type Stars.- Particle Transport in Magnetic Stellar Atmospheres.- Spectroscopic Tests of Late-Type Model Atmospheres of Dwarf Stars.- Dust in the Shells of Cool Giants and Supergiants.- NLTE Analysis of Massive OB Stars.- Formation of the K I 7699 Å Line in Sunspots.- On the Influence of Multi-Dimensional Radiative Transfer on the Energetic Contribution of the Ca K Line.- Special Session.- The Opacity Project and the Practical Utilization of Atomic Data.- New Opacity Calculations.- 40 Years Numerical Stellar Atmospheres: Concluding Remarks and Personal Considerations.