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

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

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.[1] Hydroxyl (OH) radicals can be produced by photodissociation or collisional dissociation.[2]

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.[3]


Examples



OH/IR stars



OH/IR supergiants[4]



Notes


  1. Later found to be an AGB star.

References


  1. Kemper, F.; De Koter, A.; Waters, L. B. F. M.; Bouwman, J.; Tielens, A. G. G. M. (2002). "Dust and the spectral energy distribution of the OH/IR star OH 127.8+0.0: Evidence for circumstellar metallic iron". Astronomy and Astrophysics. 384 (2): 585. arXiv:astro-ph/0201128. Bibcode:2002A&A...384..585K. doi:10.1051/0004-6361:20020036. S2CID 17649812.
  2. Goldreich, P.; Scoville, N. (1976). "OH-IR stars. I - Physical properties of circumstellar envelopes" (PDF). Astrophysical Journal. 205: 144. Bibcode:1976ApJ...205..144G. doi:10.1086/154257.
  3. Lewis, B. M. (2002). "On Dead OH/IR Stars". The Astrophysical Journal. 576 (1): 445–449. Bibcode:2002ApJ...576..445L. doi:10.1086/341534.
  4. Bowers, P. F. (December 1981). "Supergiant OH/IR stars". The Astronomical Journal. 86: 1930–1934. Bibcode:1981AJ.....86.1930B. doi:10.1086/113074. ISSN 0004-6256.


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На других языках

[de] OH/IR-Stern

OH/IR-Sterne sind hinter einer Staubhülle verborgene Rote Riesen, die Strahlung überwiegend im Infraroten und sub-mm-Bereich aussenden. Das OH im Namen stammt vom Hydroxylradikal, dessen typische Emissionslinie im Spektrum dieser Sterne enthalten ist.
- [en] OH/IR star


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