OH/IR star

File:VLT image of the surroundings of VY Canis Majoris seen with SPHERE.jpg

Very Large Telescope image of the surroundings of the red hypergiant VY Canis Majoris

An OH/IR star is an asymptotic giant branch (AGB), a red supergiant (RSG), or a red hypergiant (RHG) star that shows strong OH maser emission and is unusually bright at near-infrared wavelengths.

In the very late stages of AGB evolution, a star develops a super-wind with extreme mass loss. The gas in the stellar wind condenses as it cools away from the star, forming molecules such as water (H₂O) and silicon monoxide (SiO). This can form grains of dust, mostly silicates, which obscure the star at shorter wavelengths, leading to a strong infrared source. Hydroxyl (OH) radicals can be produced by photodissociation or collisional dissociation.

H₂O and OH can both be pumped to produce maser emission. OH masers in particular can give rise to a powerful maser action at 1612 MHz and this is regarded as a defining feature of the OH/IR stars. Many other AGB stars, such as Mira variables, show weaker OH masers at other wavelengths, such as 1667MHz or 22MHz.

Examples

OH/IR stars

• R Aquilae
• QX Puppis
• V669 Cassiopeiae
• W43A
• HV 2112

OH/IR supergiants

• S Persei
• VX Sagittarii
• V1804 Sagittarii
• VY Canis Majoris
• AH Scorpii
• MY Cephei
• PZ Cassiopeiae
• IRC −30308
• NML Cygni
• IRC +10420
• WOH G64
• IRAS 05280−6910
• IRC −10414
• RSGC1-F13