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

eclipsing binary 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 ...

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 p ...

Cassiopeia Cassiopeia or Cassiopea may refer to: Greek mythology * Cassiopeia (mother of Andromeda), queen of Aethiopia and mother of Andromeda * Cassiopeia (wife of Phoenix), wife of Phoenix, king of Phoenicia * Cassiopeia, wife of Epaphus, king of Egy ...

. Based on

parallax Parallax is a displacement or difference in the apparent position of an object viewed along two different sightline, lines of sight and is measured by the angle or half-angle of inclination between those two lines. Due to perspective (graphica ...

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 and distances of ...

mission, it is approximately from the

Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

. 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. It may sometimes be used to refer to a single star. A large group of stars bound by gravitation is generally called a ''st ...

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 alphabet, Greek or Latin letter followed by the genitive case, genitive form of its parent constellation's Latin name. The original list of Bayer design ...

. 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 January 2024) 1 ...

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

Arabic Arabic (, , or , ) is a Central Semitic languages, Central Semitic language of the Afroasiatic languages, Afroasiatic language family spoken primarily in the Arab world. The International Organization for Standardization (ISO) assigns lang ...

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 Czechoslovak astronomer. Biography He was born and died in Stará Boleslav. Among his chief achievements is the foundation of the Skalnaté Pleso Observatory and the discovery of the ...

. Professor Paul Kunitzch has been unable to find any clues as to the origin of the name. The star

Alpha Sagittarii Alpha Sagittarii (α Sagittarii, abbreviated Alpha Sgr, α Sgr), also named Rukbat , is a star in the constellation of Sagittarius. Properties Alpha Sagittarii is a blue, class B dwarf star. It does not appear particul ...

also bore the traditional name ''Ruchbah'' (as well as ''Rukbat''). In 2016, the

International Astronomical Union The International Astronomical Union (IAU; , UAI) is an international non-governmental organization (INGO) with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreach, education, and developmen ...

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 may refer to: * Something related to China * Chinese people, people identified with China, through nationality, citizenship, and/or ethnicity **Han Chinese, East Asian ethnic group native to China. **'' Zhonghua minzu'', the supra-ethnic ...

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

Iota Cassiopeiae Iota Cassiopeiae (ι Cas, ι Cassiopeiae) is a star system in the constellation Cassiopeia (constellation), Cassiopeia. The system has a combined apparent magnitude of about 4.5, making it visible to the naked eye. Based on its stel ...

, Epsilon Cassiopeiae,

Theta Cassiopeiae Theta Cassiopeiae or θ Cassiopeiae is a solitary star in the northern constellation of Cassiopeia (constellation), Cassiopeia. It shares the traditional name Marfak with μ Cassiopeiae, positioned less than half a degree to the WSW, w ...

, Nu Cassiopeiae and

Omicron Cassiopeiae Omicron Cassiopeiae (ο Cas, ο Cassiopeiae) is a triple star system in the constellation Cassiopeia (constellation), Cassiopeia. It is approximately 700 light-years from Earth, based on its stellar parallax, parallax. It is visible to t ...

. Consequently, the

Chinese name Chinese may refer to: * Something related to China * Chinese people, people identified with China, through nationality, citizenship, and/or ethnicity **Han Chinese, East Asian ethnic group native to China. **'' Zhonghua minzu'', the supra-ethni ...

for Delta Cassiopeiae itself is (, ).

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, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction of the object's light ca ...

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 gratin ...

of A5 IV, with the

luminosity class 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 gratin ...

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 ...

phase into a

giant star A giant star has a substantially larger radius and luminosity than a main-sequence (or ''dwarf'') star of the same surface temperature. They lie above the main sequence (luminosity class V in the Yerkes spectral classification) on the Hertzsp ...

. 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 Solar radius is a unit of distance used to express the size of objects in astronomy relative to the Sun. The solar radius is usually defined as the radius to the layer in the Sun's photosphere where the optical depth equals 2/3: 1\,R_ = 6.957\ti ...

. 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 ...

. 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 AU) is a unit of length defined to be exactly equal to . Historically, the astronomical unit was conceived as the average Earth-Sun distance (the average of Earth's aphelion and perihelion), before its m ...

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 "Sola ...

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