| Description |
We propose a search for far-infrared features from polycyclic aromatic hydrocarbon molecules (PAHs) in a small sample of protoplanetary disks around late-type T Tau stars. These objects were identified in the course of our large Spitzer-IRS survey of the Orion A cloud to have mid-infrared PAH features with unusual profiles, which are far too bright to explain by photoexcitation by their host stars; they must be excited by ultraviolet light from their more massive neighbors. Recent laboratory spectra of PAHs demonstrate the variation of wavelength and strength with molecule size for the far-infrared features of PAHs, a sensitivity that is lacking in the mid-infrared features. The observation of such features in disks around low-mass stars, in which we frequently see the effects of coagulation and growth among the silicate-grain population, represents an opportunity to search for size variation among the PAH population, a congruence with the PAH molecules found in the primitive meteorites, and perhaps hints of the role played by carbonaceous molecules in the assembly of solid bodies in disks. |
