The two-dimensional pressure structure of the HD 163296 protoplanetary disk as probed by multi-molecule kinematics

TL;DR

This study uses high-resolution ALMA data and a multi-molecule approach to analyze the 2D pressure structure of the HD 163296 protoplanetary disk, providing detailed insights into its kinematics and physical parameters.

Contribution

It introduces a multi-molecule kinematic analysis method that accounts for thermal stratification to characterize the disk's pressure structure in two dimensions.

Findings

Estimated stellar mass of 1.89 solar masses.

Derived disk mass of 0.12 solar masses.

Showed thermal stratification explains velocity discrepancies.

Abstract

[Abridged] Gas kinematics is a new and unique way to study planet-forming environments by an accurate characterization of disk velocity fields. High angular resolution ALMA observations allow deep kinematical analysis of disks, by observing molecular line emission at high spectral resolution. In particular, rotation curves are key tools for studying the disk pressure structure and estimating fundamental disk parameters, such as mass and radius. In this work, we explore the potential of a multi-molecule approach to gas kinematics to provide a 2D characterization of the HD 163296 disk. From the high quality data of the MAPS Large Program we extracted the rotation curves of rotational lines from seven distinct molecular species, spanning a wide radial and vertical range. To obtain reliable rotation curves for hyperfine lines, we extended standard methodologies to fit multi-component line profiles. We then sampled the likelihood of a thermally stratified model that reproduces all the rotation curves simultaneously, taking into account the molecular emitting layers and disk thermal structure. We obtained dynamical estimates of the stellar mass $M_\star=1.89$ M$_\odot$, the disk mass $M_\text{d}=0.12$ M$_\odot$, and scale radius $R_\text{c}=143$ au. We also explore how rotation curves and the parameter estimates depend on the adopted emitting layers: the disk mass proves to be the most affected by these systematics, yet the main trends we find do not depend on the adopted parameterization. Finally, we investigated the impact of thermal structure on gas kinematics, showing that the thermal stratification can efficiently explain the measured rotation velocity discrepancies between tracers at different heights. Our results show that such a multi-molecule approach, tracing a large range of emission layers, can provide unique constraints on the ($R,z$) pressure structure of protoplanetary disks.