Zeta Tauri (ζ Tauri, abbreviated Zeta Tau, ζ Tau) 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 w ...

in the zodiac constellation of

Taurus Taurus is Latin for 'bull' and may refer to: * Taurus (astrology), the astrological sign * Taurus (constellation), one of the constellations of the zodiac * Taurus (mythology), one of two Greek mythological characters named Taurus * ''Bos tauru ...

, the Bull. It has an

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 li ...

of about 3.0, which is bright enough to be seen with the naked eye. Parallax measurements place it at a distance of roughly 440 light-years 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 two components are designated Zeta Tauri A (officially named Tianguan ) and Zeta Tauri B.

Nomenclature

''ζ Tauri'' ( Latinised to ''Zeta Tauri'') 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. T ...

; it also bears the

Flamsteed designation A Flamsteed designation is a combination of a number and constellation name that uniquely identifies most naked eye stars in the modern constellations visible from southern England. They are named for John Flamsteed who first used them while co ...

of 123 Tauri. The designations of the two components as ''Zeta Tauri 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 speaking ...

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, outreach ...

(IAU). In

Chinese astronomy Astronomy in China has a long history stretching from the Shang dynasty, being refined over a period of more than 3,000 years. The ancient Chinese people have identified stars from 1300 BCE, as Chinese star names later categorized in the twe ...

, Zeta Tauri is called 天關, Pinyin: Tiānguān, formerly transliterated ''Tien Kwan'', meaning ''Celestial rontierGate'', an asterism within the Net (畢宿 ''Bì Xiù'') mansion). 天關 (Tiānguān) has also been transliterated as ''Tien Kwan''. (Technically, Tiānguān refers not just to Zeta Tauri but to the Celestial Gate asterism of which Zeta Tauri is the main star, alongside 113, 126, 128, 129, 130 and 127 Tauri .) 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 catalog and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems. It approved the name ''Tianguan'' for the component Zeta Tauri A on 30 June 2017 and it is now so included in the List of IAU-approved Star Names.

Properties

Zeta Tauri is a single-lined spectroscopic binary system, which means the two components are orbiting so close to each other that they can not be resolved with a

telescope A telescope is a device used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation. Originally meaning only an optical instrument using lenses, curved mirrors, or a combination of both to observ ...

. Instead, the orbital motion of the primary component is indicated by

Doppler effect The Doppler effect or Doppler shift (or simply Doppler, when in context) is the change in frequency of a wave in relation to an observer who is moving relative to the wave source. It is named after the Austrian physicist Christian Doppler, who d ...

shifts in the

absorption line A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used to identi ...

s in its

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 ...

. The two components are separated by an estimated distance of about 1.17

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 ...

s, or 117% of the distance from the Earth to the Sun. They are following circular orbits with a

period Period may refer to: Common uses * Era, a length or span of time * Full stop (or period), a punctuation mark Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (or rhetorical period), a concept ...

of nearly 133 days. Compared to the Sun, the primary, Zeta Tauri A, is an enormous star with more than 11 times the mass and 5–6 times the radius. It is rotating rapidly with a

projected rotational velocity Stellar rotation is the angular motion of a star about its axis. The rate of rotation can be measured from the spectrum of the star, or by timing the movements of active features on the surface. The rotation of a star produces an equatorial bulge ...

of . The companion, Zeta Tauri B, has about 94% the mass of the Sun, although it is unknown whether this is a main-sequence star, a neutron star, or a

white dwarf A white dwarf is a stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very dense: its mass is comparable to the Sun's, while its volume is comparable to the Earth's. A white dwarf's faint luminosity comes f ...

. If it is a main sequence star, then the mass indicates it may have a

stellar classification 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 th ...

of G4. The spectrum of the primary component has a

of B2 IIIpe. A luminosity class of 'III' indicates this is a giant star that has exhausted the hydrogen at its core and

evolved Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variati ...

away from the

main sequence In astronomy, the main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar H ...

. The 'p' suffix indicates an unspecified chemical peculiarity in the spectrum, while 'e' is used for stars that display

emission line A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used to identi ...

s. For

Be star Be stars are a heterogeneous set of stars with B spectral types and emission lines. A narrower definition, sometimes referred to as ''classical Be stars'', is a non-supergiant B star whose spectrum has, or had at some time, one or more Balmer e ...

s such as this, the emission lines are produced by a rotating circumstellar disk of gas, made of material that has been ejected from the star's outer envelope. An oscillatory pattern in this spectrum is being caused by a single-armed spiral density wave in the disk. The disk may be precessing from the gravitational influence of the secondary component. Zeta Tauri shows variation in its spectrum and brightness. The

General Catalogue of Variable Stars The General Catalogue of Variable Stars (GCVS) is a list of variable stars. Its first edition, containing 10,820 stars, was published in 1948 by the Academy of Sciences of the USSR and edited by B. V. Kukarkin and P. P. Parenago. Second and thi ...

lists it as an

eclipsing variable 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 ...

and a

Gamma Cassiopeiae variable A Gamma Cassiopeiae variable (γ Cassiopeiae variable) is a type of variable star, named for its prototype γ Cassiopeiae. Variability γ Cassiopeiae variables show irregular changes in brightness on a timescale of decades. These typically hav ...

, but it may not be either. Hrvoje Božić and Krešimer Pavlovski, of Hvar Observatory in Croatia, monitored the brightness of Zeta Tauri from 1981 to 1986 and noticed an eclipse like effect in the light curve. A latter study of all the available photometric data, including from the '' Hipparcos'' spacecraft, failed to confirm the presence of eclipses.

References

{{DEFAULTSORT:Zeta Tauri Tauri, Zeta B-type giants Gamma Cassiopeiae variable stars Spectroscopic binaries Taurus (constellation)

Tianguan Zeta Tauri (ζ Tauri, abbreviated Zeta Tau, ζ Tau) is a binary star in the zodiac constellation of Taurus, the Bull. It has an apparent visual magnitude of about 3.0, which is bright enough to be seen with the naked eye. Parallax measure ...

Tauri, 123

1910 Events January * January 13 – The first public radio broadcast takes place; live performances of the operas ''Cavalleria rusticana'' and ''Pagliacci'' are sent out over the airwaves, from the Metropolitan Opera House in New York Ci ...

026451 037202 BD+21 0908

Nomenclature

Properties

See also

References