Seeing Through the Ring: Near-Infrared Photometry of V582 Mon (KH 15D)

Abstract

We examine the light and color evolution of the T Tauri binary KH 15D through photometry obtained at wavelengths between 0.55 and 8.0 $\mu$m. The data were collected with ANDICAM on the 1.3 m SMARTS telescope at Cerro-Tololo Inter-American Observatory and with IRAC on the Spitzer Space Telescope. We show that the system's circumbinary ring, which acts as a screen that covers and uncovers different portions of the binary orbit as the ring precesses, has reached an orientation where the brighter component (star B) fully or nearly fully emerges during each orbital cycle. The fainter component (star A) remains fully occulted by the screen at all phases. The leading and trailing edges of the screen move across the sky at the same rate of $\sim$15 meters per second, consistent with expectation for a ring with a radius and width of $\sim$4 AU and a precession period of $\sim$6500 years. Light and color variations continue to indicate that the screen is sharp edged and opaque at \emph{VRIJH} wavelengths. However, we find an increasing transparency of the ring edge at 2.2, 3.6, and 4.5 $\mu$m. Reddening seen at the beginning of the eclipse that occurred during the CSI 2264 campaign particularly suggests selective extinction by a population of large dust grains. Meanwhile, the gradual bluing observed while star B is setting is indicative of forward scattering effects at the edge of the ring. The SED of the system at its bright phase shows no evidence of infrared excess emission that can be attributed to radiation from the ring or other dust component out to 8 microns.