Gamma Leonis
 Algieba (circled) is the γ star in the lion's mane |
|
| Observation data Epoch J2000 Equinox J2000 |
|
|---|---|
| Constellation | Leo |
| Right ascension | 10h 19m 58.35056s |
| Declination | +19° 50′ 29.3468″ |
| Apparent magnitude (V) | 2.08 (2.37/3.64) |
| Characteristics | |
| Spectral type | K0III + G7IIIb |
| U−B color index | 1.00 |
| B−V color index | 1.14 |
| Astrometry | |
| Radial velocity (Rv) | –36.24 ± 0.18 km/s |
| Proper motion (μ) |
RA: +304.30 mas/yr Dec.: –154.28 mas/yr |
| Parallax (π) | 25.07 ± 0.52mas |
| Distance | 130 ± 3 ly (39.9 ± 0.8 pc) |
| Absolute magnitude (MV) | –0.27/+0.98 |
| Orbit | |
| Period (P) | 510.3 yr |
| Semi-major axis (a) | 4.24" |
| Eccentricity (e) | 0.845 |
| Inclination (i) | 76.0° |
| Longitude of the node (Ω) | 143.4° |
| Periastron epoch (T) | 1671.3 |
| Details | |
| γ Leo A | |
| Mass | 1.23 M☉ |
| Radius | 31.88 R☉ |
| Luminosity | 320 L☉ |
| Surface gravity (log g) | 2.35 cgs |
| Temperature | 4,470 K |
| Metallicity [Fe/H] | –0.49 ± 0.12 dex |
| γ Leo B | |
| Radius | 10 R☉ |
| Luminosity | 40 L☉ |
| Surface gravity (log g) | 2.98 cgs |
| Temperature | 4,980 K |
| Metallicity [Fe/H] | –0.52 ± 0.11 dex |
| Other designations | |
| γ Leo A: HD 89484, HR 4057, SAO 81298 | |
| γ Leo B: HD 89485, HR 4058, SAO 81299 | |
| Database references | |
| SIMBAD | data |
| Exoplanet Archive | data |
| Extrasolar Planets Encyclopaedia |
data |
Gamma Leonis (γ Leonis, abbreviated Gamma Leo, γ Leo), also named Algieba, is a binary star system in the constellation of Leo. In 2009, a planetary companion around the primary was announced.
γ Leonis (Latinised to Gamma Leonis) is the star's Bayer designation.
It also bore the traditional name Algieba or Al Gieba, which originated from the Arabic الجبهة Al-Jabhah, meaning 'the forehead' (despite this meaning, the star actually appears in the mane of Leo). In 2016, the International Astronomical Union organized a Working Group on Star Names (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 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).
Algieba (gamma), Adhafera (Zeta Leonis), and Al Jabbah (Eta Leonis) have collectively been called 'the Sickle', which is an asterism formed from the head of Leo.
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 of +2.28 and is of spectral class K1-IIIbCN-0.5. The giant K star has a surface temperature of 4,470 K, a luminosity 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 170 AU apart (four times the distance between the Sun and Pluto), 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.
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