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.
Although gravitational collapse is supposed to play an essential role in the star formation process, infall motions have been always elusive to detect. So far, only a few observational signatures have been commonly used to claim for the presence of i
nfall. Often these features consist in either blue-asymmetries or absorption at red-shifted velocities (e.g., inverse P-Cygni profiles). Both signatures are based only on the shape of the line profile and they do not guarantee by themselves the presence of dominant infall motions. More robust mapping signatures can be obtained from images that angularly resolve the infalling gas. Here we present VLA observations of the ammonia inversion transitions (2,2), (3,3), (4,4), (5,5), and (6,6) towards the hot molecular core (HMC) near G31.41+0.31 that show the signatures of protostellar infall theoretically predicted by Anglada et al. (1991). The intensity of the ammonia emission is compact and sharply increases towards the centre in the blue-shifted velocity channel maps, while it shows a more flattened distribution in the red-shifted velocity channels. Additionally, the emission becomes more compact with increasing (relative) velocity for both red and blue-shifted channels. We introduce a new infall signature, the central blue spot, easily identifiable in the first-order moment maps. We show that rotation produces an additional, independent signature, making the distribution of the emission in the channel maps asymmetric with respect to the central position, but without masking the infall signatures. All these mapping signatures, which are identified here for the first time, are present in the observed ammonia transitions of G31 HMC.
We present a model aimed to reproduce the observed spectral energy distribution (SED) as well as the ammonia line emission of the G31.41+0.31 hot core. The core is modeled as an infalling envelope onto a massive star that is undergoing an intense acc
retion phase. We assume an envelope with a density and velocity structure resulting from the dynamical collapse of a singular logatropic sphere. The stellar and envelope physical properties are determined by fitting the SED. From these physical conditions, the ammonia line emission is calculated and compared with subarcsecond resolution VLA data of the (4,4) transition. The only free parameter in this line fitting is the ammonia abundance. The observed properties of the NH3(4,4) lines and their spatial distribution can be well reproduced provided it is taken into account the steep increase of the abundance in the hotter (> 100 K), inner regions of the core produced by the sublimation of icy mantles where ammonia molecules are trapped. The model predictions for the (2,2), (4,4), and (5,5) transitions are also in reasonably agreement with the single-dish spectra available in the literature. The best fit is obtained for a model with a star of 25 Msun, a mass accretion rate of 0.003 Msun/yr, and a total luminosity of 200,000 Lsun. The gas-phase ammonia abundance ranges from 2 times 10^{-8} in the outer region to 3 times 10^{-6} in the inner region. To our knowledge, this is the first time that the dust and molecular line data of a hot molecular core, including subarcsecond resolution data that spatially resolve the structure of the core, have been simultaneously explained by a physically self-consistent model. This modeling shows that massive protostars are able to excite high excitation ammonia transitions up to the outer edge (30,000 AU) of the large scale envelope.
