Wolf–Rayet star
Wolf–Rayet stars, often abbreviated as WR stars, are a rare heterogeneous set of stars with unusual spectroscopy, spectra showing prominent broad emission lines of ionised helium and highly ionised nitrogen or carbon. The spectra indicate very ...
in the constellation of
Canis Major
Canis Major is a constellation in the southern celestial hemisphere. In the second century, it was included in Ptolemy's 48 constellations, and is counted among the 88 modern constellations. Its name is Latin for "greater dog" in contrast to C ...
. 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
The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to or (AU), i.e. . The parsec unit is obtained by the use of parallax and trigonometry, and ...
(11,410
light-year
A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by the International Astr ...
s) 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 wind
A stellar wind is a flow of gas ejected from the stellar atmosphere, upper atmosphere of a star. It is distinguished from the bipolar outflows characteristic of young stars by being less collimated, although stellar winds are not generally spheri ...
s. It is estimated that it loses mass at the rate of 7x10−5
solar mass
The solar mass () is a frequently used unit of mass in astronomy, equal to approximately . It is approximately equal to the mass of the Sun. It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxie ...
es each year through winds of 1,545 km/s.
The ring nebula
NGC 2359
NGC 2359 (also known as Thor's Helmet) is an emission nebulaSEDS: NGC 2359 in the constellation is excited by the
ionising radiation
Ionizing (ionising) radiation, including nuclear radiation, consists of subatomic particles or electromagnetic waves that have enough energy per individual photon or particle to ionize atoms or molecules by detaching electrons from them. Some par ...
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
Radio is the technology of communicating using radio waves. Radio waves are electromagnetic waves of frequency between 3 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmitter connec ...
to
X-ray
An X-ray (also known in many languages as Röntgen radiation) is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelength ran ...