WR 20a is an

eclipsing binary star A binary star or binary star system is a Star system, system of two stars that are gravity, gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved ...

belonging to or recently (0.5 millions years before present) ejected from the young, massive cluster

Westerlund 2 Westerlund 2 is an obscured compact young star cluster (perhaps even a super star cluster) in the Milky Way, with an estimated age of about one or two million years. It contains some of the hottest, brightest, and most massive stars known. The ...

. It was discovered in 2004 to be one of the most massive binary systems for which the masses of the components have been accurately measured. Each star in the system has about eighty times the

mass Mass is an Intrinsic and extrinsic properties, intrinsic property of a physical body, body. It was traditionally believed to be related to the physical quantity, quantity of matter in a body, until the discovery of the atom and particle physi ...

of the

Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...

. It is not clear why this system is located away from the center of the cluster. It is possible that the system was formed in the core, but that it was ejected by dynamical interactions. V712CarLightCurve

Every 3.6 days the two stars in this system revolve around each other. Although the stars are in a very tight

orbit In celestial mechanics, an orbit (also known as orbital revolution) is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an ...

, both stars in the system are

detached A single-family detached home, also called a single-detached dwelling, single-family residence (SFR) or separate house is a free-standing residential building. It is defined in opposition to a multi-family residential dwelling. Definitions ...

. In 2004, Alceste Z. Bonanos ''et al.'' announced their discovery that the two stars

eclipse An eclipse is an astronomical event which occurs when an astronomical object or spacecraft is temporarily obscured, by passing into the shadow of another body or by having another body pass between it and the viewer. This alignment of three ...

each other on each orbit, producing a drop in brightness of about 0.4 magnitudes. The brightness is also continuously variable outside the eclipses due to the distorted shapes of the two stars. The primary and secondary minima are almost the same depth since the size and temperature of each star is almost identical. It is expected that within a million years the two will expand and come into

contact Contact may refer to: Interaction Physical interaction * Contact (geology), a common geological feature * Contact lens or contact, a lens placed on the eye * Contact sport, a sport in which players make contact with other players or objects * C ...

. A large nitrogen abundance has been measured on the surface of the stars, about six times the abundance of nitrogen measured in the sun. This nitrogen is probably produced in deeper layers of the star and pushed towards the surface by rotational mixing. A collision between the two winds of the systems has been detected in the visible as well as in

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 ...

s. The X-ray emitting region must be quite extended since it does not suffer from any eclipse.

References

{{DEFAULTSORT:WR 20a Wolf–Rayet stars Beta Lyrae variables Carina (constellation) J10235800-5745489 Carinae, V712 Spectroscopic binaries O-type supergiants

See also

References