Kinematics signature of a giant planet in the disk of AS 209

TL;DR

This study detects a large-scale kinematic perturbation in the AS 209 protoplanetary disk, consistent with a giant planet of 3-5 Jupiter masses at 100 au, using ALMA observations and semi-analytic modeling.

Contribution

It provides evidence for a giant planet in the disk based on gas kinematics, refining the planet's possible location and mass through comparison with models.

Findings

Detected a kinematic kink in CO emission lines.

A planet of 3-5 Jupiter masses at 100 au explains the perturbation.

The planet's position angle is constrained to 60-100 degrees.

Abstract

[abridged] ALMA observations of dust in protoplanetary disks are revealing the existence of sub-structures such as rings, gaps and cavities. Such morphology are expected to be the outcome of dynamical interaction between the disk and planets. However, other mechanisms are able to produce similar dust sub-structures. A solution is to look at the perturbation induced by the planet to the gas surface density and/or to the kinematics. In the case of the disk around AS 209, a prominent gap has been reported in the surface density of CO at $r \sim 100\,$au. Recently, Bae et al. (2022) detected a localized velocity perturbation in the $^{12}$CO $J=2-1$ emission along with a clump in $^{13}$CO $J=2-1$ at nearly 200 au, interpreted as a gaseous circumplanetary disk. We report a new analysis of ALMA archival observations of $^{12}$CO and $^{13}$CO J=2-1. A clear kinematics perturbation (kink) is detected in multiple channels and over a wide azimuth range in both dataset. We compared the observed perturbation with a semi-analytic model of velocity perturbations due to planet-disk interaction. The observed kink is not consistent with a planet at 200\,au as this would require a low gas disk scale height ($< 0.05$) in contradiction with previous estimate ($h/r \sim 0.118$ at $r = 100$ au). When we fix the disk scale height to 0.118 (at $r = 100$ au) we find instead that a planet of 3-5 M$_{\rm Jup}$ at 100 au induces a kinematics perturbation similar to the observed one. Thus, we conclude that a giant protoplanet orbiting at $r \sim 100\,$au is responsible of the large scale kink as well as of the perturbed dust and gas surface density previously detected. The position angle of the planet is constrained to be between 60$^{\circ}$-100$^{\circ}$. Future observations with high contrast imaging technique in the near- and mid- infrared are needed to confirm the presence and position of such a planet.