Highly Ionized Stellar Winds in Be Stars: The Evidence for Aspect Dependence

Abstract

The authors present the results of an ultraviolet survey of stellar winds in 62 Be and 43 normal B stars covering spectral types B0.5 - B5 and luminosity classes V - III. They find that the wind absorption seen in the resonance lines of C IV, Si IV, and Si III in Be stars is often the result of blended absorption from multiple shortward-shifted discrete absorption components. There is evidence of a threshold in v sin i for the presence of strong and highly variable winds in Be stars. Wind absorption in the form of shortward-shifted discrete components is observed only for Be stars having v sin i ≥ 150 km s^-1. The recent discovery that many, if not all, Be stars appear to be nonradial pulsators, and the observation that the pulsation characteristics of these stars change at v sin i = 150 km s^-1 suggests that nonradial pulsation may be important in generating the Be phenomenon. The authors also present evidence that the high-velocity and highly ionized stellar wind observed in some, but not all, moderate to high v sin i Be stars is a function of latitude.