ζ Geminorum
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Zeta Geminorum (ζ Geminorum, abbreviated Zeta Gem, ζ Gem) is a bright star with cluster components, distant
optical components Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of optical instruments, instruments that use or Photodetector, detect it. Optics usually describes t ...
and a likely spectroscopic partner in the
zodiac The zodiac is a belt-shaped region of the sky that extends approximately 8° north and south celestial latitude of the ecliptic – the apparent path of the Sun across the celestial sphere over the course of the year. Within this zodiac ...
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 first constellati ...
of
Gemini Gemini most often refers to: * Gemini (constellation), one of the constellations of the zodiac * Gemini (astrology), an astrological sign Gemini may also refer to: Science and technology Space * Gemini in Chinese astronomy, the Gemini constellat ...
— in its south, on the left 'leg' of the twin Pollux. It is a
classical Cepheid Classical Cepheids are a type of Cepheid variable star. They are young, population I variable stars that exhibit regular radial pulsations with periods of a few days to a few weeks and visual amplitudes ranging from a few tenths of a magnitude u ...
variable star A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes systematically with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are ...
, of which over 800 have been found in our galaxy. As such its regular pulsation and luminosity (proven in its class to correspond) and its relative proximity means the star is a useful calibrator in computing the
cosmic distance ladder The cosmic distance ladder (also known as the extragalactic distance scale) is the succession of methods by which astronomers determine the distances to celestial objects. A ''direct'' distance measurement of an astronomical object is possible ...
. 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, it is approximately 1,200
light-year A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by the International Astr ...
s from the
Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...
. Zeta Geminorum 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 J07041+2034. It bears traditional name Mekbuda, usually anglicised to .


Nomenclature

''ζ Geminorum'' ( Latinised to ''Zeta Geminorum'') 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 J07041+2034 A 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 ...
. The designations of the two components as WDS J03158-0849 Aa and Ab 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. It may sometimes be used to refer to a single star. A large group of stars bound by gravitation is generally called a ''st ...
s, and adopted by 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 ...
(IAU). Zeta Geminorum bore the traditional name ''Mekbuda'', from an
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 ...
phrase meaning "the lion's folded paw" (Zeta and
Epsilon Geminorum Epsilon Geminorum or ε Geminorum, formally named Mebsuta , is a star in the constellation of Gemini, on the outstretched right 'leg' of the twin Castor. The apparent visual magnitude of +3.06 makes it one of the brighter stars in this ...
(Mebsuta) were the paws of a lion). 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 decided to attribute proper names to individual stars rather than entire multiple systems. It approved the name ''Mekbuda'' for the component WDS J07041+2034 Aa on 12 September 2016 and it is now so included in the List of IAU-approved Star Names. In Chinese, (), meaning ''
Well A well is an excavation or structure created on the earth by digging, driving, or drilling to access liquid resources, usually water. The oldest and most common kind of well is a water well, to access groundwater in underground aquifers. The ...
( asterism)'' consists of eight stars in Gemini: Zeta, Mu,
Gamma Gamma (; uppercase , lowercase ; ) is the third letter of the Greek alphabet. In the system of Greek numerals it has a value of 3. In Ancient Greek, the letter gamma represented a voiced velar stop . In Modern Greek, this letter normally repr ...
, Nu, Xi,
Epsilon Epsilon (, ; uppercase , lowercase or ; ) is the fifth letter of the Greek alphabet, corresponding phonetically to a mid front unrounded vowel or . In the system of Greek numerals it also has the value five. It was derived from the Phoenic ...
, 36 and
Lambda Lambda (; uppercase , lowercase ; , ''lám(b)da'') is the eleventh letter of the Greek alphabet, representing the voiced alveolar lateral approximant . In the system of Greek numerals, lambda has a value of 30. Lambda is derived from the Phoen ...
. Zeta is (, ).香港太空館 - 研究資源 - 亮星中英對照表
, Hong Kong Space Museum. Accessed on line November 23, 2010.


Observation history

In 1844, German astronomer Julius Schmidt discovered that Zeta Geminorum varies in brightness with a period of about 10 days, although it had been suspected of variability as early as 1790. It was recognised as being related to the Cepheid class of variable stars, although was often treated as the prototype of its own class, the Geminids, because of its symmetrical light curve. In 1899, American astronomer W. W. Campbell announced the star to have a variable
radial velocity The radial velocity or line-of-sight velocity of a target with respect to an observer is the rate of change of the vector displacement between the two points. It is formulated as the vector projection of the target-observer relative velocity ...
. (This variation was independently discovered by Russian astronomer
Aristarkh Belopolsky Aristarkh Apollonovich Belopolsky (Аристарх Аполлонович Белопольский; – 16 May 1934) was a Russian and later Soviet astronomer. He was born in Moscow but his father's ancestors are from a Serbian town called B ...
, published in 1901.) Based on his observations, Campbell later published
orbital elements Orbital elements are the parameters required to uniquely identify a specific orbit. In celestial mechanics these elements are considered in two-body systems using a Kepler orbit. There are many different ways to mathematically describe the same o ...
for the binary. However, he found that the curve departed from a keplerian orbit and even suggested that it was a
triple 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 ...
to explain the irregularities. The periodic variation in radial velocity of the
Cepheid variable A Cepheid variable () is a type of variable star that pulsates radially, varying in both diameter and temperature. It changes in brightness, with a well-defined stable period (typically 1–100 days) and amplitude. Cepheids are important cosmi ...
s was later explained as being due to pulsations in the atmosphere of the star. The periodicity of the star is itself variable, a trend first noted by German astronomer
Paul Guthnick Paul Guthnick (January 12, 1879 – September 6, 1947) was a German astronomer. Born in Hitdorf am Rhein, he studied at the University of Bonn receiving his doctorate in 1901 under Friedrich Küstner. He worked from 1901 at the Royal Observat ...
in 1920, who suspected that the period change was the result of an orbiting companion. In 1930, Danish astronomer Axel Nielsen suggested that the change was instead the result in a steady decrease of about 3.6 seconds per year in the period.


Companions

Zeta Geminorum has three visible companions known since the 19th century and listed 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 ...
as B, C, and D. More recently, a possible spectroscopic companion has been listed, further faint stars close by have been catalogued, and a diffuse cluster has been identified as including Zeta Geminorum. The brightest nearby star, WDS J07041+2034 C, is the magnitude 7.6 HD 268518, 91.9" away when discovered in 1779 and 101.3" distant in 2008. It is a foreground object, only a tenth the distance of Zeta Geminorum and a high proper motion star moving rapidly compared to the more distant stars. It is a G1
main sequence In astronomy, the main sequence is a classification of stars which appear on plots of stellar color index, color versus absolute magnitude, brightness as a continuous and distinctive band. Stars on this band are known as main-sequence stars or d ...
star very similar to the sun. The closest visible companion is WDS J07041+2034 D, a 12th magnitude star measured to be 67.8" away in 2008. It was 80" distant when first measured in 1905. It appears on the sky between Zeta Geminorum and component C, but is a more distant object than either. WDS J07041+2034 B is an 11th magnitude star, 76.0" distant in 1831 and 87.4" in 2008. It is itself a
spectroscopic binary A binary star or binary star system 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 as separate stars us ...
, although little is known about the two components. The combined spectrum is of an F4 main sequence star. It is thought to be physically associated with the supergiant primary and a member of a loose cluster of stars around Zeta Geminorum. A combination of photometry, spectroscopy, and astrometry has identified 26 stars approximately 355 parsecs away, which are likely to be members of the birth cluster of Zeta Geminorum. The brightest are late B and early 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 ...
s such as the 7th magnitude stars HD 49381 and HD 50634, while the faintest detected cluster members are 12th magnitude class F main sequence stars including WDS J07041+2034 B.


Properties

Zeta Geminorum has been reported to be a spectroscopic binary on the basis of
lunar occultation An occultation is an event that occurs when one object is hidden from the observer by another object that passes between them. The term is often used in astronomy, but can also refer to any situation in which an object in the foreground blocks f ...
observations, but this has not been confirmed by other methods. Zeta Geminorum's primary (WDS J07041+2034 Aa) is a
Classical Cepheid variable Classical Cepheids are a type of Cepheid variable star. They are young, population I variable stars that exhibit regular radial pulsations with periods of a few days to a few weeks and visual amplitudes ranging from a few tenths of a magnitude u ...
that undergoes regular, periodic variation in brightness because of radial pulsations. In the
V band The V band ("vee-band") is a standard designation by the Institute of Electrical and Electronics Engineers (IEEE) for a band of frequencies in the microwave portion of the electromagnetic spectrum ranging from 40 to 75 gigahertz (GHz). The ...
, the
apparent magnitude Apparent magnitude () is a measure of the Irradiance, 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 (astronomy), ...
varies between a high of 3.68 and a low of 4.16 (with a mean of 3.93) over a period of 10.148 days. This period of variation is decreasing at the rate of 3.1 seconds per year, or 0.085 seconds per cycle. The spectral classification varies between F7Ib and G3Ib over the course of a pulsation cycle. Likewise the
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 the outer envelope varies between 5,780 K and 5,260 K, while the radius varies from 61 to 69 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 ...
. On average, it is radiating about 2,900 times the luminosity of the Sun. Membership of a cluster provides independent validation of distances determined using recent
Hubble Space Telescope The Hubble Space Telescope (HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the Orbiting Solar Observatory, first space telescope, but it is one of the largest and most ...
and
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 ...
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 ...
es. This strongly constrains the star's distance:
parsec The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to or (AU), i.e. . The parsec unit is obtained by the use of parallax and trigonometry, and ...
s. Zeta Geminorum is thus an important calibrator for the Cepheid period-luminosity relation used for establishing the
cosmic distance ladder The cosmic distance ladder (also known as the extragalactic distance scale) is the succession of methods by which astronomers determine the distances to celestial objects. A ''direct'' distance measurement of an astronomical object is possible ...
. The Gaia Data Release 2 parallax of suggests the distance is towards the top end of this range, and has a comparable margin of error.


References


External links


Zeta Geminorum (Variable Star of the Month)
{{DEFAULTSORT:Zeta Geminorum Geminorum, Zeta Gemini (constellation) Classical Cepheid variables F-type supergiants Mekbuda 2650 Geminorum, 43 052973 052973 Durchmusterung objects