A type of rapidly rotating, irregular variable of spectral type Be with an outflow of material from its equatorial region; abbr. GCAS. The formation of equatorial rings or disks is often accompanied by brightness variations of up to 1.5 mag. The prototype is the subgiant Be star Gamma Cassiopeiae, which has a magnitude range of 1.6–3.0. It underwent a major outburst in 1936–9 but now lies around magnitude 2.4. GCAS stars are a form of shell star, and the two types can change from one into the other and back again with varying levels of mass loss.