Gamma Geminorum
 Location of γ Geminorum (circled) |
|
| Observation data Epoch J2000 Equinox J2000 |
|
|---|---|
| Constellation | Gemini |
| Right ascension | 06h 37m 42.71050s |
| Declination | +16° 23′ 57.4095″ |
| Apparent magnitude (V) | 1.915 |
| Characteristics | |
| Spectral type | A1.5IV+ |
| U−B color index | +0.137 |
| B−V color index | +0.005 |
| Astrometry | |
| Radial velocity (Rv) | -12.5 km/s |
| Proper motion (μ) |
RA: +13.81 mas/yr Dec.: -54.96 mas/yr |
| Parallax (π) | 29.84 ± 2.23mas |
| Distance | 109 ± 8 ly (34 ± 3 pc) |
| Orbit | |
| Period (P) | 4,614.51 days |
| Eccentricity (e) | 0.8933 ± 0.0013 |
| Periastron epoch (T) | 244399.13 ± 0.77 |
|
Argument of periastron (ω) (secondary) |
312.60 ± 0.60° |
|
Semi-amplitude (K1) (primary) |
11.881 ± 0.068 km/s |
| Details | |
| Mass | 2.81 M☉ |
| Radius | 3.3 R☉ |
| Luminosity | 123 L☉ |
| Surface gravity (log g) | 3.60 cgs |
| Temperature | 9,260 K |
| Metallicity [Fe/H] | –0.12 dex |
| Rotational velocity (v sin i) | 15 km/s |
| Other designations | |
| Database references | |
| SIMBAD | data |
Gamma Geminorum (γ Geminorum, abbreviated Gamma Gem, γ Gem), also named Alhena, is the third-brightest star in the constellation of Gemini. It has an apparent visual magnitude of 1.9, making it easily visible to the naked eye even in urban regions. Based upon parallax measurements with the Hipparcos satellite, it is located at a distance of roughly 109 light-years (33 parsecs) from the Sun.
Alhena is an evolving star that is exhausting the supply of hydrogen at its core and has entered the subgiant stage. The spectrum matches a stellar classification of A0 IV. Compared to the Sun it has 2.8 times the mass and 3.3 times the radius. It is radiating around 123 times the luminosity of the Sun from its outer envelope at an effective temperature of 9,260 K. This gives it a white hue typical of an A-class star.
This is a spectroscopic binary system with a period of 12.6 years (4,614.51 days) in a highly eccentric Keplerian orbit.
γ Geminorum (Latinised to Gamma Geminorum) is the star's Bayer designation. The traditional name Alhena is derived from the Arabic الهنعة Al Han'ah, 'the brand' (on the neck of the camel), whilst the alternate name Almeisan is from the Arabic المیسان Al Maisan, 'the shining one.' Al Hanʽah was the name of star association consisting of this star, along with Mu Geminorum (Tejat Posterior), Nu Geminorum, Eta Geminorum (Tejat Prior) and Xi Geminorum (Alzirr). They also were associated in Al Nuḥātai, the dual form of Al Nuḥāt, 'a Camel's Hump'. 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 Alhena for this star.
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