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

TL;DR

This study models the variable brightness of HD 163296, a Herbig Ae star, attributing observed dips and brightening to changes in disk wind and bipolar cavity structures, using radiative transfer simulations.

Contribution

It introduces three detailed radiative transfer models that explain the star's brightness variability through structural changes in the disk wind and bipolar cavity.

Findings

Successful simulation of brightness drop with filled bipolar cavity.

Reproduction of near-IR brightening with structural changes in disk wind.

Quiescent state modeled without filled bipolar cavity.

Abstract

HD 163296 is a Herbig Ae star that underwent a dramatic $\sim$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 travelling 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-on-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.