AR Cassiopeiae (AR Cas) is a variable star 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 ...

of Cassiopeia. It is thought to be a member of a septuple star system, one of only two known

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 ...

s with a multiplicity of 7, the other being

Nu Scorpii Nu Scorpii (ν Scorpii, abbreviated Nu Sco, ν Sco) is a multiple star system in the constellation of Scorpius. It is most likely a septuple star system, consisting of two close groups (designated Nu Scorpii AB and CD) that are separated ...

Nomenclature

The multiple star system as a whole has the designations ADS 16795, CCDM J23300+5833, and WDS J23300+5833AB in the Aitken Double Star Catalogue, the

Catalogue of Components of Double and Multiple Stars The Catalog of Components of Double and Multiple Stars, or CCDM, is an astrometric star catalogue of double and multiple stars. It was made by Jean Dommanget and Omer Nys at the Royal Observatory of Belgium in order to provide an input catalo ...

, and the Washington Double Star Catalog respectively. AR Cassiopeiae has been referred to as IH Cas in some literature, looking similar to a variable star designation although not a valid one since the second letter of a variable star designation is always equal to the first or occurs later in the alphabet. The origin of the designation "IH Cassiopeiae" is from the 17th century catalogue and constellation map by Johannes Hevelius, which was kept in use due to the lack of a Flamsteed designation or

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. ...

for the star. It was the first star in Cassiopeia that

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 ...

's edition of Hevelius catalogued, thus "1 Hev. Cas" or "1 H. Cas" (similar to Gould designations), which becomes IH Cas through corruption.

Properties

The primary star system, AR Cassiopeiae, is a triple. AR Cassiopeiae B is located 0.800″ away from AR Cassiopeiae A. AR Cassiopeiae A itself is an Algol-type eclipsing binary with an orbital period of about 6.07 days. Its primary is a B-type main-sequence star, and the secondary an

A-type main-sequence star An A-type main-sequence star (A V) or A dwarf star is a main-sequence (hydrogen-burning) star of spectral type A and luminosity class V (five). These stars have spectra defined by strong hydrogen Balmer absorption lines. They measure between 1 ...

. The secondary star may be an Am star. Farther out are two other stars, designated components C and D. They are 76.1″, or about 1.27′, away from the central system. Their combined spectrum matches that of another B-type main-sequence star. This pair is also designated HD 221237. 67.2″ (1.12′) away from AR Cassiopeiae is another pair of stars, F and G, both F-type stars. All these stars are known to be common

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 ...

companions. However, the star listed as component E in most multiple star catalogues is an unrelated background star.

References

{{Stars of Cassiopeia Cassiopeia (constellation) Algol variables 7 Cassiopeiae, AR Durchmusterung objects 221253 8926 115990 B-type main-sequence stars