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

University of Washington
Department of Astronomy
Professor Eric Agol

KH 15D is a pre-main-sequence binary star. The KH 15D system undergoes periodic eclipses every 48 days in which it nearly disappears from view. Current theory states that the cause of the eclipses is a circumbinary ring of gas and dust that is inclined to the orbital plane. The ring of material occults the binary system and as the stars revolve around each other they are blocked from the observerís view during portions of their orbits. As time has progressed, one of the stars in the system has become completely blocked from our view. In addition, the remaining visible star spends less and less time out from behind the occulting ring as each year passes. Our predictions have estimated that the KH 15D system may disappear from our view completely as soon as 2008-2010.

Although previous researchers have developed models to describe KH 15D, the goal of our research has been to develop a complete and accurate set of model parameters. To this effect, we have attempted to expand upon current models by including new parameters, which we believe give a more physical explanation for the observed properties of KH 15D than previous publications. One of these new components accounts for a physical phenomenon theoretically caused by the surrounding dust, known as forward scattering. In this situation, a portion of the light emitted from KH 15D is scattered forward, towards the observer, causing to KH 15D to appear brighter than it would normally. This effect becomes significant specifically during ingress and egress, as well as during mid-eclipse when the hidden star approaches the edge of the ring of material. As this point, forward scattering has proven to be an important component of the model and appears to produce some of the more subtle features of the KH 15D light curve.

For the results of our research, please refer our peer-reviewed article in the July 10, 2008 issue of the Astrophysical Journal (found here) or visit the astro-ph listing of our article, which can be found here. The article contains an extended description of the KH 15D system as well as an in-depth discussion of our model and the conclusions we have reached.

For a look at our poster presented at the 209th AAS Meeting held in January of 2007, check here.

If you have questions about KH 15D or about the work that we have done, please send your queries to devin.silvia@colorado.edu.