Illumination of the circumbinary disk by an effectively point source located at the compact object. The azimuthal angle is measured from the line connecting the companion with the compact object; thus intensity 1 at azimuthal angle 0° corresponds to illumination of that patch of the circumbinary ring closest to the compact object. The illumination pattern rotates round the ring with a period of 13.08 days. The curve corresponds to a ring orbit radius of 1.6A and a mass for the compact object a little less than that of the companion.For He I the emission function was taken to be that of the illumination, apart from the eclipse range of 30° on each side of 180°, where it was set equal to zero. For Hα the illumination function was truncated initially above 0.25 (double ended arrow) to yield the emission, with a value of 0.1 in the eclipse zone (inward arrows; see text).