WR 7

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HD 56925
NGC 2359, Thor's Helmet (core).jpg
WR7 at the centre of NGC 2359
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Canis Major
Right ascension 07h 18m 29.1316s[1]
Declination −13° 13′ 01.507″[1]
Apparent magnitude (V) 11.4
Spectral type WN4-s[2]
U−B color index -0.47[3]
B−V color index 0.28[3]
Variable type None
Proper motion (μ) RA: -3.74[1] mas/yr
Dec.: 3.52[1] mas/yr
Parallax (π) 0.14 ± 0.35[4] mas
Distance 3,670[5] pc
Absolute magnitude (MV) -3.84[2]
Mass 16[2] M
Radius 1.41[2] R
Luminosity 280,000[2] L
Temperature 112,000[2] K
Other designations
WR 7, HIP 35378, HD 56925, 2MASS J07182912-1313015.
Database references

WR 7 (HD 56925) is a Wolf-Rayet star in the constellation of Canis Major. It lies at the centre of a complex bubble of gas which is shocked and partially ionised by the star's radiation and winds.

The distance is uncertain, with estimates between 3.5 kiloparsecs (11,410 lightyears) and 6.9 kiloparsecs (22,500 light years). Assuming a distance of 4.8 kiloparsecs (15,600 light-years), this star is calculated to be 280,000 times brighter than our Sun, 16 times more massive, and 1.41 times larger with a surface temperature of 112,000 Kelvin.

Stars of its kind are characterised by a rapid loss of stellar mass, driven by chemically enriched high-speed stellar winds. It is estimated that it loses mass at the rate of 7x10−5 solar masses each year through winds of 1,545 km/s.[6]

The ring nebula NGC 2359 is excited by the ionising radiation of WR7. It is also known as Thor's Helmet or the Duck Nebula. The ring is approximately 4pc across and prominent at wavelengths from radio to x-ray.[6][7]


  1. ^ a b c d Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653. Bibcode:2007A&A...474..653V. arXiv:0708.1752Freely accessible. doi:10.1051/0004-6361:20078357. 
  2. ^ a b c d e f Hamann, W. -R.; Gräfener, G.; Liermann, A. (2006). "The Galactic WN stars". Astronomy and Astrophysics. 457 (3): 1015. Bibcode:2006A&A...457.1015H. arXiv:astro-ph/0608078Freely accessible. doi:10.1051/0004-6361:20065052. 
  3. ^ a b Reed, B. Cameron (1998). "UBVβ Database for Case-Hamburg Northern and Southern Luminous Stars". The Astrophysical Journal Supplement Series. 115 (2): 271. Bibcode:1998ApJS..115..271R. doi:10.1086/313088. 
  4. ^ Gaia Collaboration (2016). "VizieR Online Data Catalog: Gaia DR1 (Gaia Collaboration, 2016)". VizieR On-line Data Catalog: I/337. Originally published in: Astron. Astrophys. 1337. Bibcode:2016yCat.1337....0G. 
  5. ^ Toalá, J. A.; Guerrero, M. A.; Chu, Y.-H.; Gruendl, R. A. (2015). "On the diffuse X-ray emission from the Wolf-Rayet bubble NGC 2359". Monthly Notices of the Royal Astronomical Society. 446: 1083. Bibcode:2015MNRAS.446.1083T. arXiv:1410.2037Freely accessible. doi:10.1093/mnras/stu2163. 
  6. ^ a b Cappa, C. E.; Goss, W. M.; Niemela, V. S.; Ostrov, P. G. (1999). "A Study of Neutral and Ionized Gas of the Wolf-Rayet Ring Nebula NGC 2359". The Astronomical Journal. 118 (2): 948. Bibcode:1999AJ....118..948C. doi:10.1086/300995. 
  7. ^ Zhekov, S. A. (2014). "X-rays from wind-blown bubbles: An XMM-Newton detection of NGC 2359". Monthly Notices of the Royal Astronomical Society. 443: 12. Bibcode:2014MNRAS.443...12Z. arXiv:1406.2463Freely accessible. doi:10.1093/mnras/stu1138. 

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