Atomic Collision Processes in Gaseous Nebulae

Abstract

Publisher Summary This chapter deals with atomic collision processes in ionized nebulae, characterized by bright emission lines in the visible spectrum. There are two main types, the diffuse nebulae, such as Orion, which are of irregular shape and contain a number of hot stars, and the planetary nebulae, which are more regular and contain a single hot star. A great deal of subsequent effort has been devoted to obtaining accurate observations and to calculating accurate reaction rates for atomic processes. It is now possible to make detailed quantitative interpretations of nebular spectra and to obtain results that are of very general astrophysical importance. For the free electrons, it is assumed that the redistribution of energy in electron–electron collisions is much faster than radiative and inelastic collision processes, and hence that a Maxwell distribution is set up. In comparing observed and calculated continuum intensities, there is a need to consider the energy distribution in the continuum, the strength of the continuum relative to the strength of the lines, and the magnitude of the discontinuity at the Balmer limit.