CIRCUMSTELLAR MATTER IN HERBIG AEBE STARS

I briefly summarize the observational evidence for large envelopes in the immediate environment of Herbig AeBe stars, and the results of sta r + envelope models. Then, I discuss two alternative possibilities to account for the observed mid-infrared fluxes, namely as the emission o f very small grains (VSG) and policyclic aromatic hydrocarbons (PAH) i n the envelope, or as due to the emission of circumstellar accretion d isks, and suggest how MIR high spatial resolution observations can dis criminate between these two hypotheses.