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]
Proper motion (μ) RA: −3.779±0.058[4] mas/yr
Dec.: 2.934±0.052[4] mas/yr
Parallax (π)0.1919 ± 0.0409[4] mas
Distanceapprox. 17,000 ly
(approx. 5,000 pc)
Absolute magnitude (MV)-3.62[2]
Mass13[2] M
Radius1.26[2] R
Luminosity229,000[2] L
Temperature112,000[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 light-years) 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 K.

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.[5]

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.[5][6]


  1. ^ a b Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357.
  2. ^ a b c d e f Sota, A.; Maíz Apellániz, J.; Morrell, N. I.; Barbá, R. H.; Walborn, N. R.; Gamen, R. C.; Arias, J. I.; Alfaro, E. J.; Oskinova, L. M. (2019). "The Galactic WN stars revisited. Impact of Gaia distances on fundamental stellar parameters". arXiv:1904.04687 [astro-ph.SR].
  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. ^ a b c Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  5. ^ 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.
  6. ^ 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. arXiv:1406.2463. Bibcode:2014MNRAS.443...12Z. doi:10.1093/mnras/stu1138.

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