Delta Cassiopeiae (δ Cassiopeiae, abbreviated Delta Cas, δ Cas) is an

eclipsing binary A binary star is a system of two stars that are 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 using a telescope as separate stars, in wh ...

star system in the northern

circumpolar constellation A circumpolar star is a star that, as viewed from a given latitude on Earth, never sets below the horizon due to its apparent proximity to one of the celestial poles. Circumpolar stars are therefore visible from said location toward the nearest po ...

of Cassiopeia. Based on

parallax Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight and is measured by the angle or semi-angle of inclination between those two lines. Due to foreshortening, nearby objects ...

measurements taken during the

Hipparcos ''Hipparcos'' was a scientific satellite of the European Space Agency (ESA), launched in 1989 and operated until 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial obj ...

mission, it is approximately from the

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

. Delta Cassiopeiae is the primary or 'A' component of a

multiple 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 speaki ...

designated WDS J01258+6014. Delta Cassiopeiae's two components are therefore designated WDS J01258+6014 Aa and Ab. Aa is officially named Ruchbah , the traditional name for the system.

Nomenclature

''δ Cassiopeiae'' ( Latinised to ''Delta Cassiopeiae'') 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. ...

. WDS J01258+6014A is its designation in the

Washington Double Star Catalog The Washington Double Star Catalog, or WDS, is a catalog of double stars, maintained at the United States Naval Observatory. The catalog contains positions, magnitudes, proper motions and spectral types and has entries for (as of June 2017) 141, ...

. It also bore the traditional names ''Ruchbah'' and ''Ksora''; the former deriving from the

Arabic Arabic (, ' ; , ' or ) is a Semitic languages, Semitic language spoken primarily across the Arab world.Semitic languages: an international handbook / edited by Stefan Weninger; in collaboration with Geoffrey Khan, Michael P. Streck, Janet C ...

word ركبة ''rukbah'' meaning "knee", and the latter appeared in a 1951 publication, ''Atlas Coeli'' (

Skalnate Pleso Atlas of the Heavens The ''Skalnaté Pleso Atlas of the Heavens'' (''Atlas Coeli Skalnaté Pleso 1950.0'') is a set of 16 celestial charts covering the entire sky. It is named after the Skalnaté Pleso Observatory in Slovakia where it was produced. The first versi ...

) by Czech astronomer

Antonín Bečvář Antonín Bečvář (; 10 June 1901 – 10 January 1965) was a Czech astronomer who was active in Slovakia. He was born (and died) in Stará Boleslav. Among his chief achievements is the foundation of the Skalnaté Pleso Observatory and the ...

. Professor Paul Kunitzch has been unable to find any clues as to the origin of the name. The star Alpha Sagittarii also bore the traditional name ''Ruchbah'' (as well as ''Rukbat''). In 2016, the

International Astronomical Union The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreac ...

organized a

Working Group on Star Names The International Astronomical Union (IAU) established a Working Group on Star Names (WGSN) in May 2016 to catalog and standardize proper names for stars for the international astronomical community. It operates under Division C – Education ...

(WGSN) to catalogue and standardize proper names for stars. The WGSN approved the name ''Ruchbah'' for the component WDS J01258+6014 Aa on 21 August 2016 and it is now so included in the List of IAU-approved Star Names (Alpha Sagittarii's primary was given the name ''Rukbat''). In

Chinese Chinese can refer to: * Something related to China * Chinese people, people of Chinese nationality, citizenship, and/or ethnicity **''Zhonghua minzu'', the supra-ethnic concept of the Chinese nation ** List of ethnic groups in China, people of va ...

, (), meaning '' Flying Corridor'', refers to an asterism consisting of Delta Cassiopeiae, Iota Cassiopeiae,

Epsilon Cassiopeiae Epsilon Cassiopeiae or ε Cassiopeiae, officially named Segin (), is a single star in the northern constellation of Cassiopeia. With an apparent visual magnitude of 3.4, this is one of the brightest stars in the constellation. The dista ...

, Theta Cassiopeiae, Nu Cassiopeiae and Omicron Cassiopeiae. Consequently, the

Chinese name Chinese names or Chinese personal names are names used by individuals from Greater China and other parts of the Chinese-speaking world throughout East and Southeast Asia (ESEA). In addition, many names used in Japan, Korea and Vietnam are often a ...

for Delta Cassiopeiae itself is (, en, the Third Star of Flying Corridor).

Properties

Delta Cassiopeiae is a possible

star system consisting of a pair of stars that orbit about each other over a period of 759 days. The combined

apparent visual magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's lig ...

of the two stars is 2.68, making it readily observable with the naked eye. Eclipses have been reported with a period of 759 days, when the brightness drops by 0.07 magnitudes. Modern studies have shown no brightness variations greater than 0.01 magnitudes. The primary member of the system (WDS J01258+6014 Aa) has a

stellar classification In astronomy, stellar classification is the classification of stars based on their stellar spectrum, spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a Prism (optics), prism or diffraction grati ...

of A5 IV, with the

luminosity class In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the ...

of IV indicating that it has exhausted the hydrogen at its core and has begun to evolve through the

subgiant A subgiant is a star that is brighter than a normal main-sequence star of the same spectral class, but not as bright as giant stars. The term subgiant is applied both to a particular spectral luminosity class and to a stage in the evolution of ...

phase into a

giant star A giant star is a star with substantially larger radius and luminosity than a main sequence, main-sequence (or ''dwarf'') star of the same effective temperature, surface temperature.Giant star, entry in ''Astronomy Encyclopedia'', ed. Patrick Moo ...

. It is calculated that it is 4% beyond the end of its main sequence lifetime, with an age of about 600 million years. It has expanded to about 3.9 times the Sun's radius. An excess infrared emission has been observed at a wavelength of 60 μm, which suggests the presence of a circumstellar

debris disk A debris disk (American English), or debris disc (Commonwealth English), is a circumstellar disk of dust and debris in orbit around a star. Sometimes these disks contain prominent rings, as seen in the image of Fomalhaut on the right. Debris dis ...

. This emission can be characterized by heat radiated from dust at a temperature of 85 K, which corresponds to an orbital radius of 88

Astronomical Unit The astronomical unit (symbol: au, or or AU) is a unit of length, roughly the distance from Earth to the Sun and approximately equal to or 8.3 light-minutes. The actual distance from Earth to the Sun varies by about 3% as Earth orbits t ...

s, or 88 times the distance of the Earth from the Sun. For comparison, the region of the remote

Kuiper belt The Kuiper belt () is a circumstellar disc in the outer Solar System, extending from the orbit of Neptune at 30 astronomical units (AU) to approximately 50 AU from the Sun. It is similar to the asteroid belt, but is far larger—20 times ...

in the

Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar S ...

extends from 30–50 AU. The

lists a 12th magnitude companion away. It is an unrelated background object.

References

{{Stars of Cassiopeia Cassiopeia (constellation) Cassiopeiae, Delta Eclipsing binaries A-type subgiants Ruchbah Cassiopeiae, 37 006686 0403 008538 Durchmusterung objects