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 ability has been confined to the brightest stars. Fabry-Perot interferometers and their modern deriva tives are bringing new ranges of resolving power to studies of atomic and ionic interstellar lines, and of course radio techniques imply exceedingly high resolution for the cool interstellar medium of molecules and radicals. Telescopes in space are extending the spectral range of these types of observations. Already the Copernicus and IUE high resolution spectrographs have given us a tantalizing glimmer of what it will be like to obtain ultraviolet spectra with resolution and signal to noise ratio approaching those obtainable on the ground. Fairly soon Space Telescope will be producing high resolution spectroscopic data of unparal leled quali ty and distance range. As often happens in astro physics the challenge is now coming from the observers to the theorists to provide interpretational tools which are adequate to the state of the data.
Table of ContentsI. Frequency redistribution problems in line formationtheory.- Observed and computed stellar line profiles: the roles played by partial redistribution, geometrical extent and expansion.- General aspects of partial redistribution and its astrophysical importance.- Kinetic aspects of redistribution in spectral lines.- Non local effects on the redistribution of resonant scattered photons.- Asymptotic properties of complete and partial frequency redistribution.- Some comments upon the line emission profile ??.- A modified Rybicki method with partial redistribution.- Redistribution functions: a review of computational methods.- The effect of abundance values on partial redistribution line computations.- Partial redistribution interlocking in the solar chromosphere.- Pannel discussion on partial redistribution.- II. Methods in line radiative transfer.- Numerical methods in radiative transfer.- Partial versus complete linearization.- Radiative transfer diagnostics: understanding multi-level transfer calculations.- A new method for solving multi-level non-LTE problems.- Escape probability methods.- Numerically stable discrete ordinate solutions of the radiative transfer equation.- NLTE spectral line formation in a three-dimensional atmosphere with velocity fields.- A code for line blanketing without local thermodynamic equilibrium.- Pannel discussion on radiative transfer methods.- III. Observational and theoretical aspects of spectral line formation in astrophysical and laborator environments.- a) Laboratory environment.- Line formation in laboratory plasmas.- b) Stellar environment.- Observational problems in spectral line formation.- Current problems of line formation in early-type stars.- Stellar surface inhomogeneities and the interpretation of stellar spectra.- The theory of line transfer in expanding atmospheres.- Computed HeII spectra for Wolf-Rayet stars.- Partial redistribution in the wind of red giants.- Modeling lines formed in the expanding chromospheres of red giants.- Transfer of Lyman-? radiation in solar coronal loops.- Pressure broadening and solar limb effect.- Hydrogen line formation in dense plasmas in the presence of a magnetic field.- c) Non-stellar environment.- A review of line formation in molecular clouds.- List of computer codes available at present.- Index of Subjects.