Imaging the Inner and Outer Gaps of the Pre-Transitional Disk of HD 169142 at 7 mm

TL;DR

This study uses 7 mm VLA observations to image large dust grains in HD 169142's protoplanetary disk, revealing gaps and asymmetries that suggest planet formation activity and a pre-transitional disk structure.

Contribution

First detailed 7 mm imaging of HD 169142's disk showing large dust grain distribution and gaps, linking these features to potential planet formation.

Findings

Detection of a bright ring at 25-30 AU with an inner cavity.

Outer gap observed from 40 to 70 AU.

Evidence of a pre-transitional disk with possible planet-induced gaps.

Abstract

We present Very Large Array observations at 7 mm that trace the thermal emission of large dust grains in the HD 169142 protoplanetary disk. Our images show a ring of enhanced emission of radius ~25-30 AU, whose inner region is devoid of detectable 7 mm emission. We interpret this ring as tracing the rim of an inner cavity or gap, possibly created by a planet or a substellar companion. The ring appears asymmetric, with the western part significantly brighter than the eastern one. This azimuthal asymmetry is reminiscent of the lopsided structures that are expected to be produced as a consequence of trapping of large dust grains. Our observations also reveal an outer annular gap at radii from ~40 to ~70 AU. Unlike other sources, the radii of the inner cavity, the ring, and the outer gap observed in the 7 mm images, which trace preferentially the distribution of large (mm/cm sized) dust grains, coincide with those obtained from a previous near-infrared polarimetric image, which traces scattered light from small (micron- sized) dust grains. We model the broad-band spectral energy distribution and the 7 mm images to constrain the disk physical structure. From this modeling we infer the presence of a small (radius ~0.6 AU) residual disk inside the central cavity, indicating that the HD 169142 disk is a pre-transitional disk. The distribution of dust in three annuli with gaps in between them suggests that the disk in HD 169142 is being disrupted by at least two planets or substellar objects.