• Source: WR 7

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 229,000 times brighter than the Sun, 13 times more massive, and 1.26 times larger with a surface temperature of 112,200 K. This makes it currently the second smallest known WN star in the galaxy, after WR 2.
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.
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.




References






External links


NASA Astronomy Picture of the Day: NGC 2359: Thor's Helmet (15 February 2014)
NASA Astronomy Picture of the Day: Thor's Helmet (5 June 2010)
NASA Astronomy Picture of the Day: The Seagull and the Duck (19 March 2010)
NGC 2359 Thor's Helmet Images of the Universe
Galactic Wolf–Rayet Catalogue
NGC 2359 Thor's Helmet - Duck Nebula (HaR)GB Astrobin

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• WR 7