A highly evolved star obscured by a thick cocoon of gas and dust which it has ejected. Most of the energy from the star is absorbed by the dust and reradiated at infrared (IR) wavelengths. The gas is rich in the hydroxyl (OH) radical, which is excited by infrared radiation to produce a powerful maser. Other circumstellar masers of water (H2O) and silicon monoxide (SiO) are also excited.
Subjects: Astronomy and Astrophysics.