Gamma Leonis is a binary star in the constellation Leo, whose components have a combined magnitude of +2.21. Its traditional name, Algieba, originates from the Arabic "Al Jabhah", meaning "the forehead". Despite this meaning, the star actually appears in the mane of Leo; the name was originally applied to several of the stars of Leo's "Sickle" (γ, ζ, and η Leo). The star's Latin name is Juba. It is known as the Twelfth Star of Xuanyuan, the Yellow Emperor, in Chinese.
Algieba marks the radiant of the annual Leonid meteor shower, which is the debris of Comet Temple-Tuttle. The Leonids return as a "meteor storm" with varying degrees of intensity every 33 years, most recently in 1998; the storm produced a fantastic rate of 100,000 meteors per hour in 1833.
Components
γ Leo is an attractive binary star discovered in 1782 by William Herschel. A modest telescope easily splits the pair under good atmospheric conditions. Its components have apparent magnitudes of +2.28 and +3.51, with an angular separation of 4.4". Even though their colors are fairly similar, the eye enhances them; some observers see them as orange and yellow, others as yellow and greenish.
At a distance of 125 light years, the two stars are at about 170 AU apart (four times the distance between Pluto and the Sun). They have an orbital period of over 500 years; only a fraction of the orbit has been observed since its discovery. A very high eccentricity (e=0.845) takes the two between 15 and 180 AU apart.
Two tenth magnitude companions appear some 6' away; one of them may actually belong to the system. If so, it is at least 14,000 AU away and would take roughly a million years to orbit Algieba proper.
Properties and Evolution
The brighter component is an orange giant of spectral class K1 IIIb. This star has a surface temperature of 4470 K, a luminosity of 180 suns, and a diameter 23 times the Sun's. The companion star belongs to spectral class G7 III, with a temperature of 4980 K, a luminosity of 50 suns, and a diameter 10 times the Sun's. Although their orbit has not been observed well enough to calculate their masses, evolutionary theory suggests that each contains about 2.35 solar masses.
Originating from the same interstellar cloud some two billion years ago, both stars have almost certainly stopped fusing hydrogen to helium in their cores, and now have expanded to great proportions. It is hard to tell how far along they might be in their giant stages. 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 (the stars have about a third of the Sun's iron content). The pair moves with rather high speed relative to the Sun (71 km/sec); that is over four times normal and suggests that they come from a different part of the galaxy.
[Adapted from STARS by Jim Kaler, Professor Emeritus of Astronomy, University of Illinois]