Variability of Disk Emission in Pre-main Sequence and Related Stars. V. Occultation Events from the Innermost Disk Region of the Herbig Ae Star HD 163296

Abstract

HD 163296 is a Herbig Ae star that underwent a dramatic ~0.8 magnitude drop in brightness in the V photometric band in 2001 and a brightening in the near-IR in 2002. Because the star possesses Herbig-Haro objects traveling in outflowing bipolar jets, it was suggested that the drop in brightness was due to a clump of dust entrained in a disk wind, blocking the line of sight toward the star. In order to quantify this hypothesis, we investigated the brightness drop at visible wavelengths and the brightening at near-IR wavelengths of HD 163296 using the Monte Carlo Radiative Transfer Code, HOCHUNK3D. We created three models to understand the events. Model 1 describes the quiescent state of the system. Model 2 describes the change in structure that led to the drop in brightness in 2001. Model 3 describes the structure needed to produce the observed 2002 brightening of the near-IR wavelengths. Models 2 and 3 utilize a combination of a disk wind and central bipolar flow. By introducing a filled bipolar cavity in Models 2 and 3, we were able to successfully simulate a jet-like structure for the star with a disk wind and created the drop and subsequent increase in brightness of the system. On the other hand, when the bipolar cavity is not filled, Model 1 replicates the quiescent state of the system.