HD 169142 VLT/VISIR images

The data probe the spatial variation of the flux in the 3.3{mu}m, 8.6{mu}m, and 11.3{mu}m aromatic bands. To constrain the radial distribution of carbonaceous nano-grains, the observations were compared to model predictions using The Heterogeneous dust Evolution Model for Interstellar Solids (THEMIS), which is integrated into the POLARIS radiative transfer code by calculating the thermal and stochastic heating of micro-and nanometer-sized dust grains for a given disk structure.

Our data show show predominant nano-particle emission at all radii (accessible with our resolution of about 0.1" or ~12AU at 3um and ~0.3", 35AU at 10um) in the HD 169142 disk. This unambiguously shows that carbonaceous nano-grains dominate radiatively the infrared spectrum in most of the disk, a finding that has been suggested in previous studies. In order to account for both VISIR and NACO emission maps, we show the need for aromatic particles distributed within the disk from the outermost regions to a radius of 20AU, corresponding to the outer limit of the inner cavity derived from previous observations.

In the inner cavity, these aromatic particles might be present but their abundance would then be significantly decreased.