Variation of Anomalous Stages of Ionization with Spectral Type for Be Stars

Abstract

One of the interesting results of ultraviolet (UV) astronomy was the discovery of ions from unexpected stages of ionization in spectra of O,B stars. The most common ions concerned are O VI and N V, but also C IV and Si IV in B stars. The presence of these ions is anomalous because generally their abundance is expected to be negligible if they are produced by photoionization by stellar radiation, either in the photosphere or in a cool circumstellar envelope (CE). The same ions are observed in the UV spectra of Be stars. Previous investigations, largely with Copernicus spectra, have reported O VI and N V in late Oe and early Be stars and Si IV in stars as cool as B5 (Marlborough, 1981 and references therein). In this paper we present the results of a preliminary survey of IUE spectra of Be stars covering a wide range of spectral type.