Spatially resolved PAH emission in the inner disks of Herbig Ae/Be stars

¹ Osservatorio Astrofisico di Arcetri, INAF, Largo E.Fermi 5, 50125 Firenze, Italy e-mail: habart@arcetri.astro.it
² Laboratoire Universitaire d'Astrophysique de Nice, UMR 6525 du CNRS, Parc Valrose, 06108 Nice Cedex 2, France

Received: 4 March 2005
Accepted: 11 October 2005

Abstract

We present adaptive-optics high-angular resolution (~0.1″) spectroscopic observations in the 3 μm region of eight well-known Herbig Ae/Be stars with circumstellar disks. We detected the aromatic emission feature at 3.3 μm 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 3.46 μm, and strong diamond features at 3.43 and 3.53 μm  in two of our flared objects (HD 100546 and HD 97048 respectively). We also detected hydrogen recombination line at 3.74 μm in practically all the objects. The emission in the polycyclic aromatic hydrocarbon (PAHs) feature at 3.3 μm and in the additional carbon dust features in the 3.4–3.5 μm 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 3.3 μm 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). The model predicts that, as observed, the 3.3 μm 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 30 AU. We find that the predicted brightness profiles reproduce the observed ones very well. This proves beyond doubt that the energetic 3.3 μm PAH emission feature takes its origin in the inner disk regions.