A star that varies in brightness as it rotates, due to an ellipsoidal shape or non-uniform surface brightness. Irregular surface brightness may result from magnetic effects, as in a magnetic variable or an oblique rotator, or the presence of starspots. See alpha2 canum venaticorum star; by draconis star; ellipsoidal variable; fk comae berenices star; rs canum venaticorum star; sx arietis star.