A maser found in the cool dusty envelope of a red giant star that is undergoing mass loss. Masers of different molecules lie in different zones around the star. Stars with oxygen-rich envelopes have circumstellar OH, H2O, and SiO masers, while stars with carbon-rich envelopes have HCN masers. The OH–IR sources have oxygen-rich envelopes with a characteristic twin-peaked OH maser at 1612 MHz and strong infrared emission from the dusty envelope.
Subjects: Astronomy and Astrophysics.