Mid-infrared emission features in WL 16

We present long-slit 7.5-13.5 mu m spectra of WL 16, a Herbig Ae star in th e rho Ophiuchi dark cloud that is surrounded by a similar to 1000 AU diamet er infrared-emitting nebula. Mid-IR emission features are detected in every I region of the nebula from center to edge, and the underlying continuum c olor temperature is approximately 10 times hotter than would be expected fr om large grains in thermal equilibrium. The 7.7 and 8.6 mu m features decre ase in intensity more rapidly with distance from the central star than the 11.3 and 12.7 mu m features, suggesting that PAH ionization effects propose d to explain similar spectral variations in other ISM sources may be import ant in WL 16 as well.