ellipsoidal variable

An ellipsoidal variable is a close binary in which the stars are so near together (though not actually in contact) that one or both are drawn out into the shape of an ellipsoid. As the components orbit one another, they are seen from different angles and therefore present a continuously varying total luminous area. The observed magnitude variations are small, typically much less than 0.2 magnitude, because there is a limit to how far a star can be stretched before it is torn apart. However, if, as in the case of Beta Lyrae stars, the components also eclipse one another, the brightness changes are much greater.