Extending the Model of KH 15D: Estimating the Effects of Forward Scattering and Curvature of the Occulting Ring Edge

TL;DR

This paper refines the model of KH 15D's eclipses by incorporating forward scattering and ring edge curvature, providing better explanations for observed light curve features and estimating dust grain size and ring distance.

Contribution

It introduces a detailed model including forward scattering and curvature effects, improving understanding of the dust ring's properties and location in KH 15D.

Findings

Dust grains have a radius of about 6 microns.

The dust ring is located at several astronomical units.

Model explains the light curve features more accurately.

Abstract

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 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 mid-eclipse. The size of the forward scattering halo indicates that the dust grains have a radius of a ~ 6 (D/3 AU) microns, 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 inside and outside eclipse independently indicates that the ring lies at a few astronomical units.