Gamma Geminorum

"Alhena" redirects here. For other uses, see Alhena (disambiguation).
γ 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 A1IV + G[3]
U−B color index +0.137[2]
B−V color index +0.005[2]
Astrometry
Radial velocity (Rv)−12.5[4] km/s
Proper motion (μ) RA: +13.81[1] mas/yr
Dec.: −54.96[1] mas/yr
Parallax (π)29.84 ± 2.23 mas[1]
Distance109 ± 8 ly
(34 ± 3 pc)
Absolute magnitude (MV)−0.68[5]
Orbit[6]
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
γ Gem A
Mass2.81[7] M☉
Radius4.95±0.32[8] R☉
Luminosity123[9] L☉
Surface gravity (log g)3.53±0.04[8] cgs
Temperature9,113±89[8] K
Metallicity [Fe/H]–0.12[10] dex
Rotational velocity (v sin i)10.7±0.2[11] km/s
γ Gem B
Mass1.07[3] M☉
Other designations
Alhena, 24 Geminorum, BD+16°1223, FK5 251, GCTP1539.00, HIP 31681, HD 47105, HR 2421, SAO 95912[1][12]
Database references
SIMBADdata

Gamma Geminorum (γ Geminorum, abbreviated Gamma Gem, γ Gem), formally named Alhena /ælˈhiːnə/,[13] is the third-brightest object in the constellation of Gemini. It 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 the Sun.[1]

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