Mid-IR spectra of inner and outer discs around three young stars

Schematic view of a circumstellar disc and the MIDI-spectra observed of the inner and outer regions of the discs around three young stars, HD 163296, HD 144432 and HD 142527 (black lines). In all of them, there are clear spectral differences between the inner and outer regions, indicating a difference in mineralogy. The general broadening of the spectral "mountain" in the inner discs is a sign of larger grains and the spectral peak at wavelength 11.3 µm indicates the presence of crystalline silicates. Also shown are best-fit model spectra (red lines), based on mixtures of the mentioned mineral species.