A kinematic excess in the annular gap and gas depleted cavity in the disc around HD 169142

TL;DR

This study uses high-resolution ALMA observations to reveal complex gas structures and kinematic features in the disc around HD 169142, indicating possible planetary influences and dynamic processes.

Contribution

First detailed ALMA imaging of gas kinematics and structures in HD 169142's disc, identifying a super-Keplerian feature and gas depletion zones.

Findings

Detection of a super-Keplerian arc feature in 12CO emission.

Identification of a central gas depleted cavity.

Evidence suggesting a potential 1 Mj planet influence.

Abstract

We present ALMA band 6 images of the 12CO, 13CO and C18O J=2-1 line emissions for the circumstellar disc around HD 169142, at ~8 au spatial resolution. We resolve a central gas depleted cavity, along with two independent near-symmetric ring-like structures in line emission: a well-defined inner gas ring [~25 au] and a second relatively fainter and diffuse outer gas ring [~65 au]. We identify a localised super-Keplerian feature or vertical flow with a magnitude of ~75m/s in the 12CO map. This feature has the shape of an arc that spans azimuthally across a PA range of ~60 to 45 degrees and radially in between the B1[26au] and B2[59au] dust rings. Through reconstruction of the gas surface density profile, we find that the magnitude of the background perturbations by the pressure support and self-gravity terms are not significant enough to account for the kinematic excess. If of planetary origin, the relative depletion in the gas-density profile would suggest a 1 Mj planet. In contrast, the central cavity displays relatively smooth kinematics, suggesting either a low mass companion and/or a binary orbit with a minimal vertical velocity component.