Scorpii beta

Acrab (Scorpii Beta/β Sco) is a multiple star located in the Constellation of the Scorpion, also known under the name of Graffias .

As opposed to what seems to indicate its designation β, Acrab is not the second most brilliant star of its constellation, but the sixth, its designation β probably having with the place of before plan which it occupies with the head of the Scorpion.

Acrab consists of several stars, the two main components of the system (noted β 1 and β 2 ) being giant of spectral Type B, separated from 14 seconds of arc, which taking into account the distance estimated at 530 light-years corresponds to approximately 2200 astronomical units. They Orbit NT one around the other in roughly 16  000 years.

β 1 have another companion, less luminous but even nearer, since separated from β 1 by only 0,5 second of arc, is approximately 80 astronomical units. Moreover β 1 seems a spectroscopic Binaire, its spectrum indicating the presence of another star, separated from 0,001 second of arc (that is to say 0,3 astronomical unit, a distance lower than that between Mercure and the Sun), with one 6,8 days orbital period.

β 2 it also is binary spectroscopic, are companion being located at 0,1 second of arc (either 16 ua).

The stellar system Acrab is thus a quintuple star, the whole of its members being of the giants of the spectral type B, i.e. very hot and very massive stars, with one rather short lifespan, about a few million years, and which will probably finish their life in Supernova E.

Acrab is located very close to the ecliptic , it thus arrives sometimes that it is occulted by the the Moon, and even, phenomenon even rarer, by one of the Planet S of the Solar system. Part of what one one knows of Acrab comes besides from the last as of these occulations, on May 13rd 1971, when the satellite of Jupiter Io occulted β 2 .

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External bond

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