A Summary of the "UIR" Bands

Paper presented at the meeting
"Diffuse Infrared Radiation and the IRTS,"
Institute of Space and Astronautical Sciences, Tokyo,
November 1996

A summary of the "Unidentified Infrared" (UIR) bands at 3-30 µm is presented. There is a group of prominent emission bands that always occur together (3.29, 6.2, 7.6/7.7, 8.6, 11.3, and 12.7 µm) and that are thought to arise from a type of aromatic hydrocarbon material or a carbonaceous material containing aromatic hydrocarbon groups. Although these emission bands are commonly attributed to polycyclic aromatic hydrocarbons (PAHs), a critical assessment of this proposed identification is presented. An alternative descriptive name for these emission bands is "carbonaceous emission bands." In addition, strong emission bands at 21 and 30 µm are also observed in some post-AGB stars. The carriers of the 21 µm and 30 µm emission bands are uncertain, but they may be SiS and MgS, respectively.

Key words: UIR bands, infrared emission bands