OH/IR star

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

Contents

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

[5]

Notes

  1. ↑ Later considered a possible extreme super-AGB star or Thorne–Żytkow object.
  2. ↑ Although various papers considered it a luminous and peculiar very late-type red supergiant with a 1974 paper deriving a spectral type of M9.1 Iap, few papers and SIMBAD considered it a Mira variable and 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". 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. ↑ Tabernero, H. M.; Dorda, R.; Negueruela, I.; Marfil, E. (2021). "On the nature of VX Sagitarii. Is it a TZO, a RSG or a high-mass AGB star?". Astronomy & Astrophysics. 646: A98. arXiv: 2011.09184 . doi:10.1051/0004-6361/202039236. S2CID   227013580.
  5. ↑ 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.
  6. ↑ Wing, R. F. (1974). "Scans and narrow-band photometry of late-type stars in the one-micron region". Highlights of Astronomy. 3: 285. Bibcode:1974HiA.....3..285W. doi:10.1017/S1539299600001994.
  7. ↑ Kolena, J.; Pataki, L. (1977). "Main-line OH emission in long-period variables and infrared stars. I. Discovery of new 1665/1667-MHz OH/IR sources". Astronomical Journal. 82: 150. Bibcode:1977AJ.....82..150K. doi: 10.1086/112020 .
  8. ↑ Humphreys, Roberta M.; Helmel, Greta; Jones, Terry J.; Gordon, Michael S. (August 2020). "Exploring the Mass Loss Histories of the Red Supergiants". The Astronomical Journal . 160 (3): 145. arXiv: 2008.01108 . Bibcode:2020AJ....160..145H. doi: 10.3847/1538-3881/abab15 . S2CID   220961677.


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