P Cygni stars
P Cygni starsA small group of hot variable stars whose prototype is the BIe star P Cygni. Their spectra show numerous strong emission lines, like those of Be stars and Wolf-Rayet stars, and sharp absorption lines that have a blueshift. The blueshifted absorption components originate in an expanding shell of low-density matter continuously ejected from the hot star. Many, like P Cygni, suffer random outbursts. The characteristic shape of the spectral lines – blueshifted absorption on an emission feature – has led to the term P Cygni profile being used for similarly shaped spectral lines in other types of astronomical bodies. In all cases it is due to an outflow of absorbing gases. See also luminous blue variables.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006