8-13 micron spectroscopy of young stars

We present 8-13 mu m spectra of 23 young stars acquired with the UKIRT CGS3 spectrometer, including T Tauri, Herbig Ae/Be, and FU Orionis stars. Silicate emission and absorption features can generally be matched with the Trapezium emissivity, by employing simple models to account for optical depth effects. Two Herbig Ae/Be objects, LkH alpha 208 and LkH alpha 198, have emission features that peak at 9.3 mu m These spectra can be adequately fitted with the Trapezium emissivity and a variable optical depth model, plus a hydrocarbon component. A different emissivity peaking at shorter wavelength is not ruled out; however, it is not a necessary conclusion from the observed spectra. Two absorption sources appear to require a narrower emissivity profile. The 11.2 mu m peak of crystalline olivine observed in comets is not seen in our YSO spectra, to a limit of 5% for emission sources and 15% for absorption profiles. Aromatic hydrocarbon emission is frequently present in our sample of Herbig Ae/Be stars and is also seen in the T Tauri stars SU Aurigae (G2 III) and DK Tau (K7). Five objects were observed at higher spectral resolution (R similar to 200) to search for spectral structure in the 11 mu m region; the aromatic hydrocarbon band at 11.2 mu m is resolved into two components at 11.22 and 11.06 mu m in LkH alpha 198 and SU Aur.