We present the results of imaging spectroscopy of the reflection nebula vdB 133 , obtained with the infrared camera and circular variable filter wheel on the Infrared Space Observatory ( ISO ) .
Our observations reveal the infrared emission features ( IEFs ) , at 6.2 , 7.7 , 8.6 , 11.3 , and 12.7 \micron , and associated 5 – 15 \mu m continuum emission .
The stellar system illuminating vdB 133 has the lowest ratio of ultraviolet ( shortward of 0.4 \mu m ) to total flux of any stars demonstrated to date to excite the IEFs and associated continuum emission from adjacent interstellar dust , as opposed to circumstellar dust .
The low fraction of UV flux from this system poses a problem for existing models for the emission mechanism and emitting material , which all require substantial UV radiation for the excitation of the IEFs and associated continuum .