OH/IR star

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

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

^ Later found to be a possible super-AGB star.

References

^ 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.
^ 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.
^ Lewis, B. M. (2002). "On Dead OH/IR Stars". The Astrophysical Journal. 576 (1): 445–449. Bibcode:2002ApJ...576..445L. doi:10.1086/341534.
^ 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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[5] Later found to be a possible super-AGB star.

[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.

[bowers1981-4] 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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