Shell profiles in Be star spectra

Extract

Although very different in shape, Be-type and Be-shell-type spectral lines are thought to arise from the same kind of circumstellar environment, a disklike envelope. The only discrimination between these two types of spectra is the inclination angle: If sufficiently high, a large column depth of circumstellar material causes partial obscuration of the stellar disk, i.e. shell absorption; otherwise a pure emission line is observed. A shell line can be considered as equivalent to P Cygni-type absorption trough for different geometry (disk instead of sphere) and kinematics (rotation instead of outflow; see Hanuschik, these proceedings).