Gamma Geminorum
 Location of γ Geminorum (circled) |
|
| Observation data Epoch J2000 Equinox J2000 |
|
|---|---|
| Constellation | Gemini |
| Right ascension | 06h 37m 42.71050s[1] |
| Declination | +16° 23′ 57.4095″[1] |
| Apparent magnitude (V) | 1.915[2] |
| Characteristics | |
| Spectral type | A1.5IV+ |
| U−B color index | +0.137[2] |
| B−V color index | +0.005[2] |
| Astrometry | |
| Radial velocity (Rv) | -12.5[3] km/s |
| Proper motion (μ) | RA: +13.81[1] mas/yr Dec.: -54.96[1] mas/yr |
| Parallax (π) | 29.84 ± 2.23[1] mas |
| Distance | 109 ± 8 ly (34 ± 3 pc) |
| Orbit[4] | |
| 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[5] M☉ |
| Radius | 3.3[6] R☉ |
| Luminosity | 123[6] L☉ |
| Surface gravity (log g) | 3.60[7] cgs |
| Temperature | 9,260[7] K |
| Metallicity [Fe/H] | –0.12[7] dex |
| Rotational velocity (v sin i) | 15[8] km/s |
| Other designations | |
| Database references | |
| SIMBAD | data |
Gamma Geminorum (γ Gem, γ Geminorum) is the third brightest star in the constellation Gemini. It has the traditional names Alhena and Almeisan. This star has an apparent visual magnitude of 1.9,[2] 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 Earth.[1]
Contents
Properties
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.[10] Compared to the Sun it has 2.8[5] times the mass and 3.3[6] times the radius. It is radiating around 123[6] times the luminosity of the Sun from its outer envelope at an effective temperature of 9,260 K.[7] This gives it a white hue typical of an A-class star.[11]
This is a spectroscopic binary system with a period of 12.6 years (4,614.51 days) in a highly eccentric Keplerian orbit.[4]
Etymology
The term Alhena is derived from the Arabic الهنعه 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 μ Gem (Tejat Posterior), ν Gem, η Gem (Tejat Prior) and ξ Gem (Alzirr). They also were associated in Al Nuḥātai, the dual form of Al Nuḥāt, "a Camel's Hump".[12]
In the catalogue of stars in the Calendarium of Al Achsasi Al Mouakket, this star was designated Nir al Henat, which was translated into Latin as Prima του al Henat, meaning the brightest of Al Henat.[13]
In Chinese, 井宿 (Jǐng Su), meaning Well (asterism), refers to an asterism consisting of γ Geminorum, μ Geminorum, ν Geminorum, ξ Geminorum, ε Geminorum, 36 Geminorum, ζ Geminorum and λ Geminorum.[14] Consequently, γ Geminorum itself is known as 井宿三 (Jǐng Su sān, English: the Third Star of Well.)[15]
In culture
Alhena was the name of a Dutch ship that rescued many people from an Italian cruise liner, the Principessa Mafalda, in October 1927.[16] In addition, the American attack cargo ship USS Alhena (AKA-9) was named after the star.
References
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- ↑ 2.0 2.1 2.2 2.3 Lua error in package.lua at line 80: module 'strict' not found.
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- ↑ 6.0 6.1 6.2 6.3 Lua error in package.lua at line 80: module 'strict' not found.
- ↑ 7.0 7.1 7.2 7.3 Lua error in package.lua at line 80: module 'strict' not found.
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- ↑ (Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.
- ↑ (Chinese) 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.
- ↑ http://www.markos.it/quaderni/plata.htm Italian account of the Principessa Malfeda.
