IMAGING THE INNER AND OUTER GAPS OF THE PRE-TRANSITIONAL DISK OF HD 169142 AT 7 mm

Abstract

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