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 instruments that use or detect it. Optics usually describes the behaviour of visible, ultravio ...
and a likely
spectroscopic partner in the
zodiac
The zodiac is a belt-shaped region of the sky that extends approximately 8° north or south (as measured in celestial latitude) of the ecliptic, the Sun path, apparent path of the Sun across the celestial sphere over the course of the year. ...
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 origins of the e ...
of
Gemini
Gemini may refer to:
Space
* Gemini (constellation), one of the constellations of the zodiac
** Gemini in Chinese astronomy
* Project Gemini, the second U.S. crewed spaceflight program
* Gemini Observatory, consisting of telescopes in the Northern ...
— in its south, on the left 'leg' of the twin
Pollux. It is a
classical Cepheid
Classical Cepheids (also known as Population I Cepheids, Type I Cepheids, or Delta Cepheid variables) are a type of Cepheid variable star. They are population I variable stars that exhibit regular radial pulsations with periods of a few days to a ...
variable star
A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are classified as ...
, 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 o ...
. 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, it is approximately 1,200
light-year
A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...
s 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 ...
.
[
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. A large group of stars bound by gravitation is generally called a '' star cluster'' or '' galaxy'', although, broadly speaki ...
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 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 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 June 2017) 141, ...
. 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. 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).
Zeta Geminorum bore the traditional name ''Mekbuda'', from an 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 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; 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 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
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 ''Well
A well is an excavation or structure created in the ground 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 ; ''gámma'') 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 re ...
, Nu, Xi, Epsilon
Epsilon (, ; uppercase , lowercase or lunate ; el, έψιλον) 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 der ...
, 36 and Lambda
Lambda (}, ''lám(b)da'') is the 11th 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 Phoenician Lamed . Lambda gave rise ...
. Zeta is (, en, the Seventh Star of Well).[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
William Wallace Campbell (April 11, 1862 – June 14, 1938) was an American astronomer, and director of Lick Observatory from 1901 to 1930. He specialized in spectroscopy. He was the tenth president of the University of California from 1923 to ...
announced the star to have a variable 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 ...
.[ (This variation was independently discovered by Russian astronomer ]Aristarkh Belopolsky
Aristarkh Apollonovich Belopolsky (Аристарх Аполлонович Белопольский) (, Moscow – 16 May 1934, Pulkovo (Saint Petersburg), Pulkovo, Leningrad Oblast, Leningrad) was a Russian astronomer. He was born in Moscow ...
, 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 ...
for the binary. However, he found that the curve departed from a keplerian orbit
Johannes Kepler (; ; 27 December 1571 – 15 November 1630) was a German astronomer, German mathematician, mathematician, astrologer, Natural philosophy, natural philosopher and writer on music. He is a key figure in the 17th-century Scienti ...
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. A large group of stars bound by gravitation is generally called a ''star cluster'' or ''galaxy'', although, broadly speaking, ...
to explain the irregularities.[ The periodic variation in radial velocity of the ]Cepheid variable
A Cepheid variable () is a type of star that pulsates radially, varying in both diameter and temperature and producing changes in brightness with a well-defined stable period and amplitude.
A strong direct relationship between a Cepheid varia ...
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 June 2017) 141, ...
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 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 Her ...
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 is a system of two star, 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 using a telescope as separa ...
, 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 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 ...
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 ...
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 (also known as Population I Cepheids, Type I Cepheids, or Delta Cepheid variables) are a type of Cepheid variable star. They are population I variable stars that exhibit regular radial pulsations with periods of a few days to a ...
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 V ...
, the apparent 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 ...
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.][ 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 (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most versa ...
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 of celestial obj ...
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 ...
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
In astronomy, a period-luminosity relation is a relationship linking the bolometric luminosity, luminosity of pulsating variable stars with their pulsation period.
The best-known relation is the direct proportionality law holding for Classical Ceph ...
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 o ...
.[ The ]Gaia Data Release 2
The ''Gaia'' catalogues are star catalogues created using the results obtained by ''Gaia'' space telescope.
The catalogues are released in stages that will contain increasing amounts of information; the early releases also miss some stars, especia ...
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