WOH G64

WOH G64

Artist's rendition of WOH G64
Observation data
Epoch J2000,0      Equinox J2000,0
Constellation Dorado (LMC)
Right ascension 04h 55m 10.482s[1]
Declination −68° 20′ 29.81″[1]
Apparent magnitude (V) 18.46[1]
Characteristics
Spectral type M5I[2]
Apparent magnitude (K) 6.85[1]
Astrometry
Radial velocity (Rv)294[2] km/s
Distance163,000 ly
(50,000 pc)
Details
Mass<25[3] M☉
Radius1,540[2] R☉
Luminosity2.8×105[2][3] L☉
Surface gravity (log g)-0.5[2] cgs
Temperature3,400[2] K
Other designations
WOH G64, 2MASS J04551048-6820298
Database references
SIMBADdata

WOH G64[4] is a red hypergiant star in the Large Magellanic Cloud satellite galaxy in the southern constellation of Dorado. It is 168,000 light years away from Earth and is one of the largest known stars, with a radius 1,540 times that of the Sun,[2] or about 1.07 billion kilometres (7.14 AU), corresponding to a volume some 3.65 billion times bigger than the Sun. If placed at the center of the Solar System, the star's surface would engulf Jupiter.

History

The star was discovered in the 1970s by Westerlund, Olander and Hedin. Like NML Cygni, the "WOH" in the star's name comes from the names of its three discoverers, but in this case refers to a whole catalogue of giant and supergiant stars in the LMC.[4] Westerlund also discovered another notable cool hypergiant star, Westerlund 1-26, found in the massive super star cluster Westerlund 1 in the constellation Ara.

Characteristics

The combination of the star's temperature and luminosity places it at the upper right corner of the Hertzsprung–Russell diagram. The star's evolved evolutionary state means that it can no longer hold on to its atmosphere due to low density, high radiation pressure, and the relatively opaque products of thermonuclear fusion. The intervening dust clouds makes the study of the star very difficult. It may be even possible that it has a bright hot companion,[2] however there has been no confirmation of this observation. The strong stellar wind of WOH G64 has created a torus-shaped cloud roughly a light year in diameter containing 3-9 solar masses of expelled material.[3]

WOG G64 varies regularly in brightness by over a magnitude with a primary period of around 800 days.[5] It has been described as a carbon-rich Mira or Long-period variable, which would necessarily be an asymptotic-giant-branch star rather than a supergiant.[6] Brightness variability has been confirmed by other researchers in some spectral bands, but it is unclear what the actual variable type is. No significant spectral variation has been found.[2]

The physical parameters found by the most recent research are consistent the largest red supergiants found elsewhere and with theoretical models of the coolest and largest possible stars (eg. the Hayashi limit). Previous results had calculated sizes approaching 2,000 R☉. Unexpectedly high luminosity values from spectral energy distribution fitting assuming spherical symmetry have been modified by modelling a dusty torus viewed nearly face on.[2][3]

See also

References

  1. 1 2 3 4 Cutri, R. M.; Skrutskie, M. F.; Van Dyk, S.; Beichman, C. A.; Carpenter, J. M.; Chester, T.; Cambresy, L.; Evans, T.; Fowler, J.; Gizis, J.; Howard, E.; Huchra, J.; Jarrett, T.; Kopan, E. L.; Kirkpatrick, J. D.; Light, R. M.; Marsh, K. A.; McCallon, H.; Schneider, S.; Stiening, R.; Sykes, M.; Weinberg, M.; Wheaton, W. A.; Wheelock, S.; Zacarias, N. (2003). "VizieR Online Data Catalog: 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)". VizieR On-line Data Catalog: II/246. Originally published in: 2003yCat.2246....0C 2246. Bibcode:2003yCat.2246....0C.
  2. 1 2 3 4 5 6 7 8 9 10 Levesque, E. M.; Massey, P.; Plez, B.; Olsen, K. A. G. (2009). "The Physical Properties of the Red Supergiant Woh G64: The Largest Star Known?". The Astronomical Journal 137 (6): 4744. arXiv:0903.2260. Bibcode:2009AJ....137.4744L. doi:10.1088/0004-6256/137/6/4744.
  3. 1 2 3 4 Ohnaka, K.; Driebe, T.; Hofmann, K. H.; Weigelt, G.; Wittkowski, M. (2009). "Resolving the dusty torus and the mystery surrounding LMC red supergiant WOH G64". Proceedings of the International Astronomical Union 4: 454. Bibcode:2009IAUS..256..454O. doi:10.1017/S1743921308028858.
  4. 1 2 Westerlund, B. E.; Olander, N.; Hedin, B. (1981). "Supergiant and giant M type stars in the Large Magellanic Cloud". Astronomy & Astrophysics Suppl. Ser. 43: 267–295. Bibcode:1981A&AS...43..267W.
  5. ↑ Fraser, Oliver J.; Hawley, Suzanne L.; Cook, Kem H. (2008). "The Properties of Long-Period Variables in the Large Magellanic Cloud from MACHO". The Astronomical Journal 136 (3): 1242. arXiv:0808.1737. Bibcode:2008AJ....136.1242F. doi:10.1088/0004-6256/136/3/1242.
  6. ↑ Soszyñski, I.; Udalski, A.; Szymañski, M. K.; Kubiak, M.; Pietrzyñski, G.; Wyrzykowski, Ł.; Szewczyk, O.; Ulaczyk, K.; Poleski, R. (2009). "The Optical Gravitational Lensing Experiment. The OGLE-III Catalog of Variable Stars. IV. Long-Period Variables in the Large Magellanic Cloud". Acta Astronomica 59: 239. arXiv:0910.1354. Bibcode:2009AcA....59..239S.
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