Xi Scorpii (ξ Sco) is a quintuple

star system A star system or stellar system is a small number of stars that orbit each other, bound by gravitational attraction. A large group of stars bound by gravitation is generally called a '' star cluster'' or '' galaxy'', although, broadly speak ...

in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the e ...

Scorpius. It was assigned this designation by

Bayer Bayer AG (, commonly pronounced ; ) is a German multinational corporation, multinational pharmaceutical and biotechnology company and one of the largest pharmaceutical companies in the world. Headquartered in Leverkusen, Bayer's areas of busi ...

, although Ptolemy had catalogued the star in

Libra Libra generally refers to: * Libra (constellation), a constellation * Libra (astrology), an astrological sign based on the star constellation Libra may also refer to: Arts and entertainment * ''Libra'' (novel), a 1988 novel by Don DeLillo Musi ...

Flamsteed John Flamsteed (19 August 1646 – 31 December 1719) was an English astronomer and the first Astronomer Royal. His main achievements were the preparation of a 3,000-star catalogue, ''Catalogus Britannicus'', and a star atlas called ''Atlas Coe ...

assigned it the designation 51 Librae, but this has fallen out of use since modern constellation boundaries assign the star to Scorpius.

Nomenclature

ξ Scorpii (Latinized to Xi Scorpii) is the star's

Bayer designation A Bayer designation is a stellar designation in which a specific star is identified by a Greek or Latin letter followed by the genitive form of its parent constellation's Latin name. The original list of Bayer designations contained 1,564 stars. ...

. Xi Scorpii has no proper name, though it was erroneously known as ''Graffias'' before that name was applied to

Beta Scorpii Beta Scorpii (β Scorpii, abbreviated Beta Sco, β Sco) is a multiple star system in the southern zodiac constellation of Scorpius. It bore the traditional proper name of Acrab , though the International Astronomical Union now regards ...

. Its Flamsteed designation is ''51 Librae''. When the modern constellation boundaries were drawn, Xi Scorpii was assigned to Scorpius, and the Flamsteed designation fell out of use. The five stars of Xi Scorpii all have different designations. Depending on the catalogue, however, some designations apply to more than one stars. Xi Scorpii A, B, and C appear very close together in the sky and are often given one designation, while D and E are sometimes also given a single designation. Struve's catalogue of multiple stars includes the pair AB and C as Σ1998 and the pair D and E as Σ1999.

Properties

The Xi Scorpii system consists of five stars in two groups separated by about 4.7 arcminutes (or 0.08°) on the sky. The brighter group contains Xi Scorpii A, B, and C. A and B are both yellow-white F-type stars. A is slightly brighter and warmer. They are separated by 0.744

arcsecond A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of one degree. Since one degree is of a turn (or complete rotation), one minute of arc is of a turn. The na ...

s on average, and orbit around a common center once every 45.9 years. The dimmer, seventh-magnitude Xi Scorpii C orbits this pair at about ten times the distance, having a separation of around 7.6 arcseconds. The second group contains Xi Scorpii D and E. Both D and E are

K-type main-sequence star A K-type main-sequence star, also referred to as a K-type dwarf or an orange dwarf, is a main-sequence (hydrogen-burning) star of spectral type K and luminosity class V. These stars are intermediate in size between red M-type main-sequence stars ...

s, which are separated by about 11.9 arcseconds. They are known to be associated to each other and with the rest of the stars, because all stars share similar

proper motion Proper motion is the astrometric measure of the observed changes in the apparent places of stars or other celestial objects in the sky, as seen from the center of mass of the Solar System, compared to the abstract background of the more dista ...

s. A sixth component, the 11th-magnitude Xi Scorpii F, is located 81 arcseconds from D, but is not known to be gravitationally bound to the other five components. Therefore, it is not considered to be part of the system.

References

External links

* * * {{Stars of Scorpius Scorpii, Xi Scorpius (constellation) 6 5 F-type main-sequence stars G-type main-sequence stars K-type main-sequence stars Librae, 51 Durchmusterung objects 9540 1 078727 38 5977 8 144069 70 87 88