The organic-rich carbonaceous component of dust aggregates in circumstellar disks: Effects of its carbonization on infrared spectral features of its magnesium-rich olivine counterpart

We model dust in comets, protoplanetary disks, and debris disks as aggregates consisting of submicron-sized grains with a silicate core and an organic-rich carbonaceous mantle. By computing the infrared (IR) spectra of the aggregates, we show that the degree of carbonization determines the positions of infrared peaks characteristic of magnesium-rich crystalline silicates. We discuss our results in terms of processing of organic materials by ultraviolet irradiation, ion bombardments, and thermal devolatilization. A comparison between the model IR spectra of the aggregates and the observed spectra of dust in circumstellar disks reveals that at least one third of the organic refractory component has suffered from carbonization in a very short timescale.