A star of spectral type B, on or near the main sequence, which exhibits emission lines of hydrogen (hence the ‘e’ suffix); Be stars are sometimes referred to as ‘classical’ to distinguish them from Herbig Be stars (see Herbig Ae/be Star) and B[e] stars. The emission is usually variable, as is the brightness of the star. This class, which represents about 20% of the B-star population, consists of rapidly rotating B stars which have thrown off an equatorial disk or ring. Excitation of the gas in this disk by the star’s ultraviolet light causes the emission. Equatorial rotation velocities are 250–450 km/s, significantly higher than for normal B stars. Bright Be stars include Achernar and Gamma Cassiopeiae. See also Gamma Cassiopeiae Star; Shell Star.