2008ApJ...681.1377S

The periodic eclipses of the pre-main-sequence binary KH 15D have been explained by a circumbinary dust ring inclined to the orbital plane, which causes occultations of the stars as they pass behind the ring edge. We compute the extinction and forward scattering of light by the edge of the dust ring in order to explain (1) the gradual slope directly preceding total eclipse, (2) the gradual decline at the end of ingress, and (3) the slight rise in flux at mideclipse. The size of the forward-scattering halo indicates that the dust grains have a radius of a∼6(D/3 AU) µm, where D is the distance of the edge of the ring from the system barycenter. This dust size estimate agrees well with estimates of the dust grain size from polarimetry, adding to the evidence that the ring lies at several AU. Finally, the ratio of the fluxes during an eclipse to those not during an eclipse independently indicates that the ring lies at a few AU.