Ultraviolet spectra of planetary nebulae

Abstract

The short-wave spectra of gaseous and, in particular, of planetary nebulae have for long attracted the attention of astrophysicists. In the 6Os the first attempts were made aimed at plotting the expected spectra of planetary nebulae in the ultraviolet, in the region of wavelengths shorter than 3000 ~ and down to 912 A (Code, 1960; Aller, 1961). This was followed by an analysis of the expected forbidden lines (some thirty in number) in the ultraviolet, and the possibility of the discovery with their help of some physical parameters was indicated (Gurzadyan, 1965; Osterbrock, 1963). Even more accurate calculations were made aimed at finding the intensities of more powerful ultraviolet lines in the spectrum of highly excited nebulae (Fowler, 1968). At the same time, pre-estimates were made of atomic parameters for various transitions -the collision strengths, the probabilities of forbidden transitions, etc. (Czyzak et al., 1968; Garstang, 1968). The attempts at drawing up various models of planetary nebulae also bear on the above studies (Harrington, 1968; Kirkpatrick, 1970).