2006A&A...449.1067H

We present adaptive-optics high-angular resolution (∼0.1'') spectroscopic observations in the 3µm region of eight well-known Herbig Ae/Be stars with circumstellar disks. We detected the aromatic emission feature at 3.3µm for four out of six of our objects with flared disks (HD 169142, HD 97048, HD 100453, HD 100546), some additional features at 3.4 and 3.46µm, and strong diamond features at 3.43 and 3.53µm in two of our flared objects (HD 100546 and HD 97048 respectively). We also detected hydrogen recombination line at 3.74µm in practically all the objects. The emission in the polycyclic aromatic hydrocarbon (PAHs) feature at 3.3µm and in the additional carbon dust features in the 3.4-3.5µm region is, for the first time, spatially resolved in all the sources where the features are detected. The full-width at half-maximum sizes that we derive are typical of emission arising in a circumstellar disk. On the other hand, the continuum emission remains unresolved, with the exception of HD 97048 where it is marginally resolved. We compared the observed spatial distribution of the 3.3µm PAH feature and the adjacent continuum to the predictions of a disk model that includes transiently heated small grains and PAHs, in addition to large grains in thermal equilibrium (Habart et al., 2004A&A...427..179H). The model predicts that, as observed, the 3.3µm PAH emission feature is significantly broader than that of the adjacent continuum and also that about 50% of its integrated intensity comes from a radius R< 30 AU. We find that the predicted brightness profiles reproduce the observed ones very well. This proves beyond doubt that the energetic 3.3µm PAH emission feature takes its origin in the inner disk regions.