Infrared Space Observatory mid-infrared spectra of reflection nebulae

We present 5-15 mu m imaging spectroscopy of the reflection nebulae vdB 17 (NGC 1333), vdB 59 (NGC 2068), vdB 101, vdB 111, vdB 133, and vdB 135, obta ined with the infrared camera and circular variable filter wheel on the Inf rared Space Observatory (ISO). These nebulae are illuminated by stars with T-eff = 3,600-19,000 K, implying UV (lambda < 400 nm) to total stellar flux ratios of F-(lambda<400nm)/F-total = 0.01-0.87. We detect the infrared emi ssion features (IEFs) at 6.2, 7.7, 8.6, 11.3, and 12.7 mu m, broad emission features at 6-9 mu m and 11-13 mu m, and 5-15 mu m continuum emission, fro m the interstellar medium in vdB 17, vdB 59, and vdB 133 (F-(lambda<400nm)/ F-total = 0.22-0.87), and place upper limits on the emission from the inter stellar medium in vdB 101, vdB 111, and vdB 135 (F-(lambda<400nm)/F-total = 0.01-0.20). Our goal is to test predictions of models attributing the IEFs to polycyclic aromatic hydrocarbons (PAHs). Interstellar models predict PA Hs change from singly ionized to neutral as the UV intensity, G(0), decreas es. The ratio of PAH emission at 6-10 mu m to PAH emission at 10-14 pm is e xpected to be 10 times higher in ionized than in neutral PAHs. We observe n o spectroscopic differences with varying T-eff. We analyze the spectra of v dB 17 and vdB 59 as a function of distance from the star to see how the spe ctra depend on G(0) within each source. The only quantitative difference we find is a broadening of the 7.7 mu m IEF at G(0) = 20-60 within vdB 17. We observe only a 40% change in the 6-10 pm to 10-14 pm flux ratio over G(0) = 20-6 x 10(4).