Wolf–Rayet star

Wolf–Rayet stars (often referred to as WR stars) are a heterogeneous set of stars with unusual spectra showing prominent broad emission lines of highly ionised helium and nitrogen or carbon. The spectra indicate very high surface temperatures of 30,000 K to around 200,000 K, surface enhancement of heavy elements, and strong stellar winds.

Classic (or Population I) Wolf–Rayet stars are evolved, massive stars, O-type stars over 20 solar masses when they were on the main sequence, that have now completely lost their outer hydrogen and are fusing helium or heavier elements in the core. A subset of WR stars are the central stars of planetary nebulae (CSPNe), post Asymptotic Giant Branch stars that were similar to the Sun while on the main sequence, but have now ceased fusion and shed their atmospheres to show a bare carbon-oxygen core. Another group (type WNh) show hydrogen lines in their spectra and are young extremely massive stars still fusing hydrogen at the core, with nitrogen mixed to the surface and strong radiation-driven mass loss. They are all highly luminous due to their high temperatures, thousands of times the bolometric luminosity of the Sun (L_☉) for the CSPNe, hundreds of thousands L_☉ for the Population I WR stars, to over a million L_☉ for the WNh stars, although not exceptionally bright visually since most of their radiation output is in the ultraviolet.

Rayet

Rayet is a commune in the Lot-et-Garonne department in south-western France.

See also

Rayet (crater)

Rayet is a small lunar impact crater that lies on the far side of the Moon, past the northeast limb. It lies to the southwest of the larger crater Millikan, and east of the comparably sized Petrie.

This crater is roughly circular in shape, with a sharp edge and relatively featureless inner walls that slope downward to the nearly level interior floor. The diameter of the floor is roughly two-thirds that of the crater. This formation has not been notably worn by impact erosion, and is otherwise undistinguished.

This feature is named after the French astronomer Georges Rayet (1839–1906).

Satellite craters

By convention these features are identified on lunar maps by placing the letter on the side of the crater midpoint that is closest to Rayet.

References

Wolf–Rayet

Wolf–Rayet (WR) can mean:

WR 104

Coordinates: 18^h 02^m 04.07^s, −23° 37′ 41.2″

WR 104 is a binary star system located about 7,500 light years from Earth, surrounded by a distinctive pinwheel nebula. The primary is a Wolf-Rayet star and the secondary is a main sequence OB star. Within the next few hundred thousand years, the system has a small probability of firing a gamma-ray burst in the general direction of the Earth.

Structure

WR 104 is surrounded by a distinctive dusty pinwheel nebula over 200 astronomical units long formed by interaction between the stellar winds of the two stars as they rotate and orbit. The spiral is composed of dust that would normally be prevented from forming by WR 104's intense radiation were it not for the star's companion. The region where the stellar wind from the two massive stars interacts compresses the material enough for the dust to form, and the rotation of the system causes the spiral-shaped pattern. The round appearance of the spiral leads to the conclusion that the system is seen almost pole on, and an almost circular orbital period of 220 days had been assumed from the pinwheel outflow pattern.