WR 2 is a Wolf-Rayet star located around 8,000 light years away from

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

in the constellation of Cassiopeia, in the

stellar association A stellar association is a very loose star cluster, looser than both open clusters and globular clusters. Stellar associations will normally contain from 10 to 100 or more stars. The stars share a common origin, but have become gravitationally u ...

Cassiopeia OB1. It is smaller than the Sun, but due to a

temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied o ...

over it is 282,000 times as luminous as the Sun. With a radius of 89% that of the Sun, it is the smallest known WN star in the

Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye ...

. WR 2 is considered to be a member of the nitrogen sequence of WR stars, but completely lacks lines of N_III, N_IV, N_V, and He_I. Its spectrum is dominated by broad rounded emission lines of He_II, leading to the classification of WN2-b (for broad). It is now given the spectral type of WN2-w (for weak), due to the relative strength of the continuum and lack of extremely intense emission lines. It is the only galactic WN2 star known. Weak-lined Wolf-Rayet stars often have hot luminous companions which dilute the emission. WR 2 does have a companion, but it is much fainter than the primary and not thought to be the cause of the weak-lined spectrum. WR 2 is the smallest and hottest WN star known in the galaxy. Its unusual rounded emission lines are thought to be due to extremely fast rotation, although the exact rotation rate is not known. Estimates range from 500 km/s to approximately the breakup rate for the star of 1,900 km/s. The high temperature also leads to a very fast

stellar wind A stellar wind is a flow of gas ejected from the 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 spherically symmetric. D ...

of 1,800 km/s, although the overall rate of mass loss is one of the lowest for any Wolf-Rayet star. The combination of a massive Wolf-Rayet star and rapid rotation is likely to result in a gamma-ray burst when the star explodes as a

supernova A supernova is a powerful and luminous explosion of a star. It has the plural form supernovae or supernovas, and is abbreviated SN or SNe. This transient astronomical event occurs during the last evolutionary stages of a massive star or when ...

X-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...

s have been detected from WR 2 although they may not be due to colliding winds as is common for massive stars.

References

{{Stars of Cassiopeia Cassiopeia (constellation) Wolf–Rayet stars 6327 005100