Of-WN evolution: spectral types and effective temperatures

Abstract

Because of the growing evidence (Conti 1976, Snow and Morton 1976, Chiosi et al. 1978, de Loore etal. 1977) that some Of stars are evolving into WN stars, we reexamine the classification of WN stars. There are four schemes for classifying WN stars, those of the IAU (1938), Hiltner and Schild (1966), Smith (1968), and Walborn (1974). All of these schemes involve estimating by eye the ratio of the nitrogen line strengths. Walborn's scheme is the most useful because he avoids problems that may arise from the use of helium lines. In other respects Walborn's scheme gives WN classifications similar to those found by Smith.