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]
Primary1 Gem A
Companion1 Gem B
Period (P)4,877.6±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)
Semi-amplitude (K1)
11.34±0.03 km/s
Semi-amplitude (K2)
8.07±0.04 km/s
Primary1 Gem Ba
Companion1 Gem Bb
Period (P)9.60 d
Semi-major axis (a)0.002638±0.000005"
(0.1234±0.0001 au)
Eccentricity (e)0.0024±0.0005
Inclination (i)93.2±1.1°
Longitude of the node (Ω)137.5±1.9°
Argument of periastron (ω)
Semi-amplitude (K1)
52.0±0.1 km/s
Semi-amplitude (K2)
87.7±0.2 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
NSV 16765, BD+23°1170, FK5 1163, HD 41116, HIP 28734, HR 2134, SAO 77915
Database references

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, by 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.

In 1948, 1 Geminorum was discovered to be a close double star whilst using it to focus a telescope for observations of the planet Uranus. From initial observations of the spectrum, it was estimated that both components were giants and that the secondary was itself double.[8] Radial velocity variations had been found in 1906, but only one set of absorption lines could be detected in the spectrum and it was not possible to calculate a reliable orbit until 1976.[9]

1 Geminorum is a triple star system 0.17 degree south of the ecliptic. The primary component of the system, 1 Geminorum A, is a K-type red clump giant star around twice the mass of the Sun.[10] Component A is orbited by a spectroscopic binary pair of stars at a separation of about 9.4 astronomical units every 4877.6 days. The two secondary components, 1 Geminorum Ba and Bb, have not been resolved, but regular periodic Doppler shifts in the spectrum indicate orbital motion of a binary pairing consisting of an F-type subgiant and a solar-mass star that may be G-type, separated by approximately 0.1234 astronomical units.[4]

In 1893, a 14th magnitude companion was reported by Sherburne Wesley Burnham 94 from the naked-eye star,[11] but it is a distant background object.[12]

1 Geminorum is listed as a suspected variable star with an amplitude of 0.05 magnitudes.[13]


  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:0708.1752. 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 h 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/9911002. Bibcode:1999A&A...352..555A.
  8. ^ Kuiper, Gerard P. (1948). "A New Bright Double Star". The Astrophysical Journal. 108: 542. Bibcode:1948ApJ...108..542K. doi:10.1086/145095.
  9. ^ Griffin, R. F.; Radford, G. A. (1976). "Spectroscopic binary orbits from photoelectric radial velocities. Paper 10: 1 Geminorum B". The Observatory. 96: 188. Bibcode:1976Obs....96..188G.
  10. ^ Zhao, G.; Qiu, H. M.; Mao, Shude (2001). "High-Resolution Spectroscopic Observations of Hipparcos Red Clump Giants: Metallicity and Mass Determinations". The Astrophysical Journal. 551 (1): L85. Bibcode:2001ApJ...551L..85Z. doi:10.1086/319832.
  11. ^ Mason, Brian D.; Wycoff, Gary L.; Hartkopf, William I.; Douglass, Geoffrey G.; Worley, Charles E. (2001). "The 2001 US Naval Observatory Double Star CD-ROM. I. The Washington Double Star Catalog". The Astronomical Journal. 122 (6): 3466. Bibcode:2001AJ....122.3466M. doi:10.1086/323920.
  12. ^ Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  13. ^ 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.