The Profiles of the 3–12 Micron Polycyclic Aromatic Hydrocarbon Features

We present spectra of the 3.3 m and 11.2 m polycyclic aromatic hydrocarbon (PAH) features of a large number of stellar sources, planetary nebulae, reflection nebulae, H ii regions, and galaxies, obtained with Infrared Space Observatory Short Wavelength Spectrometer. Clear variations are present in the profiles of these features. Most of the sources show a symmetric 3.3 m feature peaking at 3.290 m, while only very few show an asymmetric 3.3 m feature peaking at a slightly longer wavelength. The profiles of the 11.2 m feature are distinctly asymmetric. The majority of the sources has a 11.2 m feature peaking between 11.20 and 11.24 m, with a very steep blue rise and a low tail-to-top ratio. A few sources show a 11.2 m feature with a peak position of 11.25 m, a less steep blue rise, and a high tail-to-top ratio. The sources are classified independently on the basis of the 3.3 and 11.2 m feature profiles and peak positions. Correlations between these classes and those based on the 6–9 m features (Peeters et al.) are found. In particular, sources with the most common profiles in the 6–9 m region also show the most common 3.3 and 11.2 m feature profiles. However, the uncommon profiles do not correlate with each other. Also, these classifications depend on the type of object. In general, H ii regions, nonisolated Herbig AeBe stars and young stellar objects show the same profiles for all 3–12 m features. Many planetary nebulae and post–asymptotic giant branch stars show uncommon feature profiles. The