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...

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...

Spectral line formation theory is at the heart of astrophysical diagnostic. Our knowledge of abundances, in both stellar and interstellar contexts, comes almost enti- rely from line analysis, as does a major fraction of our ability to model stellar atmospheres. As new facets of the universe become observable so the techniques of high reso- lution spectroscopy are brought to bear, with great reward. Improved instruments, such as echelle spectrographs, employ- ing detectors of high quantum efficiency, have revolutioned our ability to observe high quality line profiles, although until now this...