Gamma Leonis (γ Leonis, abbreviated Gamma Leo, γ Leo), also named Algieba , 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 in the

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 Leo. In 2009, a planetary companion around the primary was announced.

Nomenclature

''γ Leonis'' ( Latinised to ''Gamma Leonis'') is the

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 ...

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 A and B components of the binary are often referred to as γ¹ Leonis and γ² Leonis, respectively. It also bore the traditional name ''Algieba'' or ''Al Gieba'', which originated 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 ...

''الجبهة'' ''Al-Jabhah'', meaning 'the forehead' (despite this meaning, the star actually appears in the mane of Leo). 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 catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016 included a table of the first two batches of names approved by the WGSN, which included ''Algieba'' for this star. The star's traditional

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

name was ''Juba''. It is known as 軒轅十二 (the Twelfth Star of Xuanyuan) in Chinese (Xuanyuan is the name of the

Yellow Emperor The Yellow Emperor, also known as the Yellow Thearch or by his Chinese name Huangdi (), is a deity ('' shen'') in Chinese religion, one of the legendary Chinese sovereigns and culture heroes included among the mytho-historical Three Soverei ...

). Algieba, along with

Zeta Leonis Zeta Leonis (ζ Leonis, abbreviated Zeta Leo, ζ Leo), also named Adhafera , is a third-magnitude star in the constellation of Leo (constellation), Leo, the lion. It forms the second star (after Gamma Leonis) in the blade of the sickle, ...

Regulus Regulus is the brightest object in the constellation Leo and one of the brightest stars in the night sky. It has the Bayer designation designated α Leonis, which is Latinized to Alpha Leonis, and abbreviated Alpha Leo or α Leo. Re ...

Mu Leonis Mu Leonis (μ Leonis, abbreviated Mu Leo, μ Leo), also named Rasalas , is a star in the constellation of Leo. The apparent visual magnitude of this star is 3.88, which is bright enough to be seen with the naked eye. Based upon an annual p ...

Epsilon Leonis Epsilon Leonis (ε Leo, ε Leonis) is the fifth-brightest star in the constellation Leo, consistent with its Bayer designation Epsilon. It is known as Algenubi or Ras Elased Australis. Both names mean "the southern star of the lion's hea ...

and

Eta Leonis Eta Leonis (η Leo, η Leonis) is a fourth-magnitude star in the constellation Leo, about away. Properties Eta Leonis is a white supergiant with the stellar classification A0Ib. Since 1943, the spectrum of this star has served as o ...

, have collectively been called ''the Sickle'', which is an asterism that marks the head of Leo.

Stellar system

The bright binary system in Leo with orange-red and yellow or greenish-yellow components is visible through a modest telescope under good atmospheric conditions. To the naked eye, the Algieba system shines at mid-second magnitude, but a telescope easily splits the pair. The brighter component has an

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 ...

of +2.28 and is of

spectral class 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 the ...

K1-IIIbCN-0.5. The giant K star has a surface temperature of , a

luminosity Luminosity is an absolute measure of radiated electromagnetic power (light), the radiant power emitted by a light-emitting object over time. In astronomy, luminosity is the total amount of electromagnetic energy emitted per unit of time by a st ...

180 times that of the Sun, and a diameter 23 times that of the Sun. The companion star has an apparent magnitude of +3.51 and belongs to the spectral class G7IIICN-I. The giant G star has a temperature of 4,980 K, a luminosity of 50 times that of the Sun, and a diameter 10 times that of the Sun. With angular separation of just over 4″, the two stars are at least apart (four times the distance between the Sun and

Pluto Pluto (minor-planet designation: 134340 Pluto) is a dwarf planet in the Kuiper belt, a ring of trans-Neptunian object, bodies beyond the orbit of Neptune. It is the ninth-largest and tenth-most-massive known object to directly orbit the S ...

), and have an orbital period of over 500 years. Because the orbital period is so long, only a fraction of the full path has been observed since discovery. Both stars are almost certainly true giants, meaning that they have stopped fusing

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...

helium Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table. ...

in their cores and have expanded to great proportions. Although there has been too little observation of their

orbit In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as a p ...

to calculate their masses, comparison with evolutionary calculations suggests that each are about double the mass of the Sun. Originating from the same interstellar cloud some two billion years ago, the stars have

iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in f ...

contents about a third that of the Sun. It is hard to tell how far along they might be in their life cycle. They both may be fusing helium in their cores, or they could be giants in development, with quiet helium cores that are waiting to fire up. The chemical composition at the surface, which is influenced by age, suggests the former.

Variability

γ Leonis is a suspected variable star, with a

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 ...

range of 1.84 to 2.03. It is not known which of the two components is variable. In 1959, the star was mistakenly published as an

eclipsing binary 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 ...

due to a typographical error when referring to Y Leonis.

Planetary system

On November 6, 2009, the discovery of a planetary companion around primary star γ¹ Leonis (γ Leonis A) was announced. The

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 ...

measurements suggest two additional periodicities of 8.5 and 1,340 days. The former is likely due to stellar pulsation, whereas the latter could be indicative of the presence of an additional planetary companion with 2.14

Jupiter mass Jupiter mass, also called Jovian mass, is the unit of mass equal to the total mass of the planet Jupiter. This value may refer to the mass of the planet alone, or the mass of the entire Jovian system to include the moons of Jupiter. Jupiter is b ...

es, moderate eccentricity (e=0.13) and located at 2.6 AU away from the giant star. Nevertheless, the nature of such a signal is still unclear and further investigations are needed to confirm or rule out an additional substellar companion.

References

External links

Algieba
at Jim Kaler's Stars

{{DEFAULTSORT:Gamma Leonis Leo (constellation) Leonis, Gamma Leonis, 41 Binary stars Planetary systems with one confirmed planet Algieba K-type giants G-type giants 4057 089484 050583 BD+20 2467 Suspected variables