Episodic mass loss and narrow lines in Gamma Cassiopeiae and in otherearly-type stars.

Abstract

High-resolution ultraviolet spectra obtained with the IUE of the B0.5 IVe star γ Cas have revealed conspicuous changes in the profiles of the resonance doublet lines of C IV, N V, and Si IV. In 18 out of the 28 available spectra, narrow absorption components of varying strengths are found at the blueshifted side of the rest wavelength. The central velocities of the narrow lines are between -650 and -1500 km s^-1. A comparison of the occurrence and properties of the narrow lines in γ Cas with those in a sample of 26 OB stars analyzed by Lamers, Gathier, and Snow, suggests that these lines may be a common phenomenon in all early-type stars, irrespective of luminosity class or Be characteristics. It is suggested that these lines are formed in a rapidly expanding region of the stellar wind which has a higher density than the ambient "quiet" wind, and which has resulted from an enhanced mass flux of the star during a short time (about 1 day).