HD 56925

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HD 56925
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Canis Major
Right ascension 07h 18m 29.1316s
Declination −13° 13′ 01.507″
Apparent magnitude (V) 11.4
Spectral type WN4-s[1]
U−B color index -0.47
B−V color index 0.28
Variable type None
Proper motion (μ) RA: -3.74 mas/yr
Dec.: 3.52 mas/yr
Parallax (π) -0.66 ± 2.55 mas
Distance 3662 ly
(1124[citation needed] pc)
Absolute magnitude (MV) -3.84[1]
Mass 16[1] M
Radius 1.41[1] R
Luminosity 280,000[1] L
Temperature 112,000[1] K
Age 20 million[citation needed] years
Other designations
WR 7, HIP 35378.
Database references

In astronomy WR 7 or HD 56925/HIP 35 378 is a Wolf-Rayet star which is a central part of the nebula NGC 2359 (also known as the Thor's Helmet Nebula) in the constellation of Canis Major.

The distance is uncertain, varying 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.

Studies of the interaction between WR 7 and the surrounding nebula assumes a distance of 5 kiloparsecs, and have discovered the existence of a HI region of 70x37 kiloparsecs that expands at 12 km/s, possibly created by the progenitor of the current star, a type-O main sequence star. It seems likely that there is a bow shock acting on the southern edge of the nebula, possibly reduced when the star was at the stage of red supergiant.


  1. ^ a b c d e f Hamann, W. -R.; Gräfener, G.; Liermann, A. (2006). "The Galactic WN stars". Astronomy and Astrophysics 457 (3): 1015. arXiv:astro-ph/0608078. Bibcode:2006A&A...457.1015H. doi:10.1051/0004-6361:20065052.  edit