Beta Draconis, a name Latinized from β Draconis, is a

binary star 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 ...

system and the third-brightest

star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

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 ...

Draco Draco is the Latin word for serpent or dragon. Draco or Drako may also refer to: People * Draco (lawgiver) (from Greek: Δράκων; 7th century BC), the first lawgiver of ancient Athens, Greece, from whom the term ''draconian'' is derived * ...

. The two components are designated Beta Draconis A (officially named Rastaban , the traditional name of the system) and B respectively. With a 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 2.79, it is bright enough to be easily seen with the naked eye. Based upon

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 from 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 ...

astrometry satellite, it lies at a distance of about from the

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

. The system is drifting closer with a

radial velocity The radial velocity or line-of-sight velocity, also known as radial speed or range rate, of a target with respect to an observer is the temporal rate of change, rate of change of the distance or Slant range, range between the two points. It is e ...

of −21 km/s. The binary system consists of a

bright giant A giant star is a star with substantially larger radius and luminosity than a main-sequence (or ''dwarf'') star of the same surface temperature.Giant star, entry in ''Astronomy Encyclopedia'', ed. Patrick Moore, New York: Oxford University Press ...

orbited by a

dwarf Dwarf or dwarves may refer to: Common uses *Dwarf (folklore), a being from Germanic mythology and folklore * Dwarf, a person or animal with dwarfism Arts, entertainment, and media Fictional entities * Dwarf (''Dungeons & Dragons''), a humanoid ...

companion once every four

millennia A millennium (plural millennia or millenniums) is a period of one thousand years, sometimes called a kiloannum (ka), or kiloyear (ky). Normally, the word is used specifically for periods of a thousand years that begin at the starting point (ini ...

or so. The companion is about 11 magnitudes fainter than the primary star, and the two are separated by . The

spectrum A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum. The word was first used scientifically in optics to describe the rainbow of colors i ...

of the primary, Beta Draconis A, matches 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 G2Ib-IIa, showing mixed features of a

and a

supergiant star Supergiants are among the most massive and most luminous stars. Supergiant stars occupy the top region of the Hertzsprung–Russell diagram with absolute visual magnitudes between about −3 and −8. The temperature range of supergiant stars ...

, and is listed as a standard star for that spectral class. It is about 65 million years old and is currently undergoing its first convective

dredge-up A dredge-up is any one of several stages in the evolution of some stars. By definition, during a ''dredge-up'', a convection zone extends all the way from the star's surface down to the layers of material that have undergone fusion. Consequently, th ...

. Compared to the Sun, Beta Draconis A is an enormous star with six times

the mass Mass is the main Eucharistic liturgical service in many forms of Western Christianity. The term ''Mass'' is commonly used in the Catholic Church, in the Western Rite Orthodox, in Old Catholic, and in Independent Catholic churches. The term is ...

and roughly 40 times the radius. At this size, it is emitting about 950 times the

luminosity of the Sun The solar luminosity (), is a unit of radiant flux (power emitted in the form of photons) conventionally used by astronomers to measure the luminosity of stars, galaxies and other celestial objects in terms of the output of the Sun. One nominal s ...

from its outer envelope at an

effective temperature The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation. Effective temperature is often used as an estimate of a body's surface temperature ...

of 5,160 K, giving it the yellow hue of a

G-type star A G-type main-sequence star (Spectral type: G-V), also often, and imprecisely called a yellow dwarf, or G star, is a main-sequence star (luminosity class V) of spectral type G. Such a star has about 0.9 to 1.1 solar masses and an effective tempe ...

. The star has a particularly strong chromospheric emission that is generating

X-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...

and far-UV radiation. There is a detectable

magnetic field A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...

with a longitudinal field strength of . Beta Draconis lies on or near the

cepheid instability strip The unqualified term instability strip usually refers to a region of the Hertzsprung–Russell diagram largely occupied by several related classes of pulsating variable stars: Delta Scuti variables, SX Phoenicis variables, and rapidly oscilla ...

, yet only appears to be a microvariable with a range of about 1/100th of a magnitude. It was confirmed as a variable star with a range of about 1/100th of a magnitude by Gabriel Cristian Neagu using data from the TESS and Hipparcos missions. The variability was reported to the AAVSO (American Association of Variable Star Observers), in the Variable Star Index.

Nomenclature

''β Draconis'' ( Latinised to ''Beta Draconis'') is the system'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. ...

. The designations of the two components as ''Beta Draconis A'' and ''B'' derive from the convention used by the Washington Multiplicity Catalog (WMC) for

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 ...

s, and adopted by 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 ...

(IAU). It bore the traditional name ''Rastaban'', which has also been used for

Gamma Draconis Gamma Draconis (γ Draconis, abbreviated Gamma Dra, γ Dra), formally named Eltanin , is a star in the northern constellation of Draco. Contrary to its gamma-designation (historically third-ranked), it is the brightest star in Draco at m ...

. This name, less commonly written ''Rastaben'', derives 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 ...

phrase ''ra's ath-thu'ban'' "head of the serpent/dragon". It was also known as ''Asuia'' and ''Alwaid'' , the latter from the Arabic ''al-ʽawāʼidh'' "the old mother camels". In 2016, the IAU 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 ''Rastaban'' for the component Beta Draconis A on 21 August 2016 and it is now so included in the List of IAU-approved Star Names. Beta Draconis is part of the asterism of the Mother Camels (Arabic ''al'awa'id''), along with Gamma Draconis (Eltanin),

Mu Draconis Mu Draconis (μ Draconis, abbreviated Mu Dra, μ Dra) is a multiple star system near the head of the constellation of Draco. With a combined magnitude of 4.92, it is visible to the naked eye. Based on parallax estimates by the ...

(Erakis),

Nu Draconis Nu Draconis (also known as ν Dra, ν Draconis, or traditionally as Kuma ) is a double star in the constellation Draco. The respective components are designated ν1 Draconis and ν2 Draconis. The second component is a spectroscopic bin ...

(Kuma) and

Xi Draconis Xi Draconis (ξ Draconis, abbreviated Xi Dra, ξ Dra) is a double or binary star in the northern circumpolar constellation of Draco. It has an apparent visual magnitude of 3.75. Based upon parallax measurements, it is located at a dis ...

(Grumium), which was later known as the ''Quinque Dromedarii''. 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 ...

, (), meaning '' Celestial Flail'', refers to an asterism consisting of Beta Draconis, Xi Draconis, Nu Draconis, Gamma Draconis and

Iota Herculis Iota Herculis (ι Herculis, ι Her) is a fourth-magnitude variable star system in the constellation Hercules, consisting of at least four stars all about away. The brightest is a β Cephei variable, a pulsating star. Visibility Iot ...

. 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 Beta Draconis itself is known as (, en, the Third Star of Celestial Flail).

References

External links

* {{DEFAULTSORT:Beta Draconis G-type bright giants G-type supergiants Binary stars Draco (constellation) Draconis, Beta BD+52 2065 Draconis, 23 159181 085670 6536 Rastaban