1 Geminorum

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1 Geminorum
Gemini constellation map.svg
Red circle.svg
Location of 1 Geminorum (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Gemini
Right ascension 06h 04m 07.21544s[1]
Declination +23° 15′ 48.0401″[1]
Apparent magnitude (V) 4.15[2] (4.77 / 5.50)[3]
Spectral type K0III + (F6IV + G2V)[4]
U−B color index +0.53[5]
B−V color index +0.83[5]
Radial velocity (Rv)22.39 ± 0.28[6] km/s
Proper motion (μ) RA: -1.61[1] mas/yr
Dec.: -118.33[1] mas/yr
Parallax (π)21.39 ± 0.03[4] mas
Distance152.5 ± 0.2 ly
(46.75 ± 0.07 pc)
Absolute magnitude (MV)0.84[7]
Orbit: 1 Gem A/B[4]
Period (P)4877.6 ± 1.0 d
Semi-major axis (a)0.2010 ± 0.0004"
(9.399 ± 0.010 au)
Eccentricity (e)0.3709 ± 0.0004
Inclination (i)59.33 ± 0.04°
Longitude of the node (Ω)353.67 ± 0.04°
Periastron epoch (T)2445119 ± 2.3
Argument of periastron (ω)
21.29 ± 0.09°
Semi-amplitude (K1)
11.34 ± 0.03 km/s
Semi-amplitude (K2)
8.07 ± 0.04 km/s
1 Gem A
Mass1.94 ± 0.01[4] M
Surface gravity (log g)3.1[6] cgs
Metallicity [Fe/H]-0.01[6] dex
1 Gem Ba
Mass1.707 ± 0.005[4] M
1 Gem Bb
Mass1.012 ± 0.003[4] M
Other designations
BD+23° 1170, FK5 1163, HD 41116, HIP 28734, HR 2134, SAO 77915
Database references
1 Gem A
1 Gem B

1 Geminorum (1 Gem) is a star in the constellation Gemini. Its apparent magnitude is 4.15.

In the 19th century, John Flamsteed numbered the brighter stars in each constellation from west to east, and 1 Geminorum was the first star listed in Gemini. It is also listed in the Bright Star Catalogue as star 2134, usually designated HR 2134 with the HR standing for the Harvard Revised catalog, the precursor to the Bright Star Catalogue.

1 Geminorum is a triple star system 0.17 degree south of the ecliptic. The primary component of the system is a K-type red giant star. It is almost twice the mass of the Sun. It is orbited by a spectroscopic binary pair of stars at a separation of about 9.4 astronomical units every 4877.6 days. It has not been resolved, but periodic Doppler shifts in the spectrum indicate the orbital motion of two separate stars. The pair, an F-type subgiant and a solar-mass star that may be G-type, are separated by 0.1234 astronomical units.[4]

1 Geminorum is listed as a suspected variable star with an amplitude of 0.05 magnitudes.[8]


  1. ^ a b c d van Leeuwen, F.; et al. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752Freely accessible. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. 
  2. ^ Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues. 2237. Bibcode:2002yCat.2237....0D. 
  3. ^ "Sixth Catalog of Orbits of Visual Binary Stars". United States Naval Observatory. Retrieved 15 May 2017. 
  4. ^ a b c d e f g Lane, Benjamin F.; Muterspaugh, Matthew W.; Griffin, R. F.; Scarfe, C. D.; Fekel, Francis C.; Williamson, Michael H.; Eaton, Joel A.; Shao, M.; Colavita, M. M.; Konacki, Maciej (2014). "The Orbits of the Triple-Star System 1 Geminorum from Phases Differential Astrometry and Spectroscopy". The Astrophysical Journal. 783: 3. Bibcode:2014ApJ...783....3L. doi:10.1088/0004-637X/783/1/3. 
  5. ^ a b Mermilliod, J.-C. (1986). "Compilation of Eggen's UBV data, transformed to UBV (unpublished)". Catalogue of Eggen's UBV data. Bibcode:1986EgUBV........0M. 
  6. ^ a b c Massarotti, Alessandro; Latham, David W.; Stefanik, Robert P.; Fogel, Jeffrey (2008). "Rotational and Radial Velocities for a Sample of 761 Hipparcos Giants and the Role of Binarity". The Astronomical Journal. 135: 209. Bibcode:2008AJ....135..209M. doi:10.1088/0004-6256/135/1/209. 
  7. ^ Allende Prieto, C.; Lambert, D. L. (1999). "Fundamental parameters of nearby stars from the comparison with evolutionary calculations: masses, radii and effective temperatures". Astronomy and Astrophysics. 352: 555–562. arXiv:astro-ph/9911002Freely accessible. Bibcode:1999A&A...352..555A. 
  8. ^ Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/gcvs. Originally published in: 2009yCat....102025S. 1. Bibcode:2009yCat....102025S.