Carbon IV absorption troughs in the ultraviolet spectra of Be stars - Gone with the wind?

IUE observations of five Be stars reveal striking and previously unrecognized forms of stellar wind variability. Broad C IV double-lambda 1548,1550 absorption troughs, which underlie shortward-shifted narrow absorption components, may disappear or reappear. The C IV equivalent width can vary by a factor approximately equal to or greater than 5 on a time scale of approximately 3 months, implying considerable changes in the mass loss rate or source of superionization in the wind or both. The shifted narrow absorption components may themselves disappear or reappear, and are not necessarily superposed on a broad absorption trough. Some narrow components may persist at an essentially constant velocity; such components may occur at any velocity in the wind. The profiles of narrow components may display an abrupt longward edge and extended shortward absorption.