Unveiling the gas and dust disk structure in HD 163296 using ALMA observations

TL;DR

This study uses ALMA observations and radiative transfer modeling to reveal the detailed vertical and radial structure of the gas and dust in the protoplanetary disk around HD 163296, highlighting differences in size and temperature.

Contribution

It provides the first sub-millimeter imaging of the vertical structure of a gaseous disk and refines models of the dust and gas distribution around HD 163296.

Findings

Gaseous disk is over twice as large as the dust disk.

Vertical structure details of the gaseous disk are unveiled at sub-millimeter frequencies.

CO gas depletion occurs at temperatures below 20 K.

Abstract

Aims: The aim of this work is to study the structure of the protoplanetary disk surrounding the Herbig Ae star HD 163296. Methods: We have used high-resolution and high-sensitivity ALMA observations of the CO(3-2) emission line and the continuum at 850 microns, as well as the 3- dimensional radiative transfer code MCFOST to model the data presented in this work. Results: The CO(3-2) emission unveils for the first time at sub-millimeter frequencies the vertical structure details of a gaseous disk in Keplerian rotation, showing the back- and the front-side of a flared disk. Continuum emission at 850 microns reveals a compact dust disk with a 240 AU outer radius and a surface brightness profile that shows a very steep decline at radius larger than 125 AU. The gaseous disk is more than two times larger than the dust disk, with a similar critical radius but with a shallower radial profile. Radiative transfer models of the continuum data confirms the need for a sharp outer edge to the dust disk. The models for the CO(3-2) channel map require the disk to be slightly more geometrically thick than previous models suggested, and that the temperature at which CO gas becomes depleted (frozen-out) from the outer regions of the disk midplane is T < 20 K, in agreement with previous studies.