DO THE INFRARED-EMISSION FEATURES NEED ULTRAVIOLET EXCITATION

We present the results of imaging spectroscopy of the reflection nebul a vdB 133, obtained with the infrared camera and circular variable fil ter wheel on the Infrared Space Observatory. Our observations reveal t he infrared emission features (IEFs), at 6.2, 7.7, 8.7, 11.3, and 12.7 mu m, and associated 5-15 mu m continuum emission. The stellar system illuminating vdB 133 has the lowest ratio of ultraviolet (shortward o f 0.4 mu m) to total flux of any stars demonstrated to date to excite the IEFs and associated continuum emission from adjacent inter-stellar dust, as opposed to circumstellar dust. The low fraction of UV flux f rom this system poses a problem for existing models for the emission m echanism and emitting material, which all require substantial UV radia tion for the excitation of the IEFs and associated continuum.