Transient components in the Lyman lines of hot stars Evidence for the ejection of shells or puffs on very short timescales

The existence of H I transient components in the stellar wind of Epsilon Per toward eight early type stars observed by the Copernicus satellite is systematically investigated. It is shown that such transient components are indeed present in the spectra of five of these stars and have characteristics very similar to the one found in the case of Epsilon Per. It is shown that such components can be interpreted in terms of coherent 'puffs' or shells of matter ejected by the stars. They would be caused by an increase of the stellar mass loss rate by a factor of 1.5 to 3 during one hour or less, and would be accelerated more slowly than the quiet wind. It is suggested that such events must be due to instabilities in these stars which are all slightly evolved stars ranging in spectral types between O9 and B1. The instabilities are probably similar to those in Beta Cephei stars, i.e., nonradial pulsations.