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One of the highest excitation nebulae AB7 in the Magellanic Clouds.jpg
AB7 is one of the highest excitation nebulae in the Magellanic Clouds.
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Tucana
Right ascension 01h03m35.93s[1]
Declination -72°03′22.0″[1]
Apparent magnitude (V) 13.016[1]
Spectral type WN4 + O6I[1]
U−B color index -1.21[1]
B−V color index -0.62[1]
Distance 197,000 ly
(61,000 pc)
Absolute magnitude (MV) -6.1 (combined)[2]
Mass 28 + 54[2] M
Radius ~6[2] R
Luminosity 1,200,000 (WR component)[2] L
Temperature 80,000[2] K
Other designations
AB 7, SMC WR 7, OGLE SMC-SC9 37124, SBC9 2395
Database references

AB7, also known as SMC WR7, is a binary star in the Small Magellanic Cloud galaxy,[2] consisting of one Wolf-Rayet star, highly evolved massive star, and a mid-age massive companion of spectral type O. They orbit in a period of 19.579 days.[3]

These exceptional stars have very strong stellar winds and they continuously eject energetic particles — like the "solar wind" from the Sun — but some 10 million to 1 billion times more intensely than our star. These powerful winds exert an enormous pressure on the surrounding interstellar material and forcefully shape those clouds into "bubbles", well visible in the photos by their blue colour.

AB7 is particularly remarkable: the associated huge nebula and He-II region indicate that this star is one of the hottest WR-star known so far, with a surface temperature in excess of 80,000 degrees,[2] although other studies suggest a slightly lower temperature.[3][1] The luminosity of the WR component is primarily in the ultra-violet and so depends strongly on the actual temperature since observations are made in the visual and infra-red. Just outside this nebula, a small network of green filaments is visible - they are the remains of another supernova explosion.


  1. ^ a b c d e f g Bonanos, A. Z.; Lennon, D. J.; Köhlinger, F.; Van Loon, J. Th.; Massa, D. L.; Sewilo, M.; Evans, C. J.; Panagia, N.; Babler, B. L.; Block, M.; Bracker, S.; Engelbracht, C. W.; Gordon, K. D.; Hora, J. L.; Indebetouw, R.; Meade, M. R.; Meixner, M.; Misselt, K. A.; Robitaille, T. P.; Shiao, B.; Whitney, B. A. (2010). "Spitzer SAGE-SMC Infrared Photometry of Massive Stars in the Small Magellanic Cloud". The Astronomical Journal 140 (2): 416. arXiv:1004.0949. Bibcode:2010AJ....140..416B. doi:10.1088/0004-6256/140/2/416. 
  2. ^ a b c d e f g Niemela, V. S.; Massey, P.; Testor, G.; Gimenez Benitez, S. (2002). "The massive Wolf-Rayet binary SMC WR7". Monthly Notices of the Royal Astronomical Society 333 (2): 347. doi:10.1046/j.1365-8711.2002.05395.x.  edit
  3. ^ a b Foellmi, C.; Moffat, A. F. J.; Guerrero, M. A. (2003). "Wolf--Rayet binaries in the Magellanic Clouds and implications for massive-star evolution -- I. Small Magellanic Cloud". Monthly Notices of the Royal Astronomical Society 338 (2): 360. doi:10.1046/j.1365-8711.2003.06052.x.  edit