Epoch J2000,0 Equinox J2000,0
|Right ascension||04h 55m 10.49s|
|Declination||−68° 20′ 29.08″|
|Apparent magnitude (V)||18.46|
|Apparent magnitude (K)||6.85|
|Radial velocity (Rv)||~300 km/s|
|Absolute magnitude (MV)||-8.9|
|Radius||1,540 - 1,730 R☉|
|Surface gravity (log g)||-0.5 cgs|
WOH G64, 2MASS J04551048-6820298
WOH G64 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, 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.
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. Westerlund also discovered another notable cool hypergiant star, Westerlund 1-26, found in the massive super star cluster Westerlund 1 in the constellation Ara.
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, 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.
The star 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. 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.
- 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.
- 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. doi:10.1017/S1743921308028858.
- 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.
- 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. Bibcode:2009AcA....59..239S.
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