The Light Curve of the Weakly-Accreting T Tauri Binary KH 15D from 2005-10: Insights into the Nature of its Protoplanetary Disk

TL;DR

This study presents a detailed analysis of the light curve of the KH 15D binary system from 2005-2010, revealing insights into its warped circumbinary disk and ongoing eclipses caused by disk precession.

Contribution

It provides new observational evidence of the disk's structure and variability, supporting a model of a warped, thin, optically thick disk influencing the system's photometric behavior.

Findings

The binary's photospheres are fully obscured, visible only by scattered light.

Periodic brightness variations depend solely on binary phase, explaining previous light curve features.

Color changes during minima suggest a third light source or changing disk reflectance.

Abstract

Photometry of the unique pre-main sequence binary system KH 15D is presented, spanning the years 2005-2010. This system has exhibited photometric variations and eclipses over the last 50 years caused by a precessing circumbinary disk. Advancement of the occulting edge across the binary orbit has continued and the photospheres of both stars are now completely obscured at all times. The system is now visible only by scattered light, and yet it continues to show a periodic variation on the orbital cycle with an amplitude exceeding two magnitudes. This variation, which depends only on the binary phase, has likely been present in the data since at least 1995. It can, by itself, account for shoulders on the light curve prior to ingress and following egress, obviating the need for components of extant models such as a scattering halo around star A or forward scattering from a fuzzy disk edge. A plausible source for the variable scattering component is reflected light from the far side of a warped occulting disk. We have detected color changes in V-I of several tenths of a magnitude to both the blue and red that occur during times of minima. These may indicate the presence of a third source of light (faint star) within the system, or a change in the reflectance properties of the disk as the portion being illuminated varies with the orbital motion of the stars. The data support a picture of the circumbinary disk as a geometrically thin, optically thick layer of perhaps mm or cm-sized particles that has been sculpted by the binary stars and possibly other components into a decidedly nonplanar configuration. A simple (infinitely sharp) knife-edge model does a good job of accounting for all of the recent (2005-2010) occultation data.