Interferometric evidence for quantum heated particles in the inner region of protoplanetary disks around Herbig stars

Abstract

Context. To understand the chemical composition of planets, it is important to know the chemical composition of the region where they form in protoplanetary disks. Because of its fundamental role in chemical and biological processes, carbon is a key element to trace. Aims. We identify the carriers and processes behind the extended near-infrared (NIR) flux observed around several Herbig stars. Methods. We compared the extended NIR flux from objects in the PIONIER Herbig Ae/Be survey with their flux in the policyclic aromatic hydrocarbon (PAH) features. HD 100453 is used as a benchmark case to investigate the influence of quantum heated particles, like PAHs or very small carbonaceous grains, in more detail. We use the Monte Carlo radiative transfer code MCMax to do a parameter study of the quantum heated particle (QHP) size and scale height and examine the influence of quantum heating on the amount of extended flux in the NIR visibilities. Results. There is a correlation between the PAH feature flux of a disk and the amount of its extended NIR flux. We find that very small carbonaceous grains create the observed extended NIR flux around HD 100453 and still lead to a realistic SED. These results cannot be achieved without using quantum heating effects, e.g. only with scattered light and grains in thermal equilibrium. Conclusions. It is possible to explain the extended NIR emission around Herbig stars with the presence of carbonaceous, quantum heated particles. Interferometric observations can be used to constrain the spatial distribution and typical size of carbonaceous material in the terrestrial planet forming region.