Shape of the trapping potential function U(r) for two hypothetical stars: the M-type star with half the solar mass and 4 times the rotation rate, and the A-type star with twice the solar mass and 23 times the solar rotation rate. The ratio of stellar radiation pressure to gravity β was assumed to be 0.1 for the M star and 0.4 for the A star. The cases of no corotation (solid line), maximum corotation (dotted), and moderate corotation (dashed line) are shown. The horizontal lines show the conserved energy values for each case.