Article · Wikipedia archive · Last revised Jul 20, 2026

Phi Geminorum

Phi Geminorum, Latinized from φ Geminorum, is a binary star in the constellation Gemini, to the southeast of Pollux. It is visible to the naked eye with an apparent visual magnitude of 4.95. Based upon an annual parallax shift of 14.66 mas, this system is located around 220 light years from the Sun.

Last revised
Jul 20, 2026
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φ Geminorum
Location of φ Geminorum (circled in red)
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Gemini1
Right ascension 07h 53m 29.81390s2
Declination +26° 45′ 56.8252″2
Apparent magnitude (V) 4.953
Characteristics
Evolutionary stage main sequence4
Spectral type A3 V5
U−B color index +0.083
B−V color index +0.103
Astrometry
Radial velocity (Rv)+8.06 km/s
Proper motion (μ) RA: −34.692 mas/yr
Dec.: -30.102 mas/yr
Parallax (π)14.66±0.73 mas2
Distance220 ± 10 ly
(68 ± 3 pc)
Absolute magnitude (MV)+0.811
Orbit
Period (P)581.751 d7
Eccentricity (e)0.07
Details
Mass1.98 M☉
Luminosity36.59 L☉
Surface gravity (log g)4.08 cgs
Temperature8,551±2918 K
Rotational velocity (v sin i)16510 km/s
Age6378 Myr
Other designations
φ Gem, 83 Geminorum, BD+27°1499, FK5 1207, HD 64145, HIP 38538, HR 3067, SAO 79774.11
Database references
SIMBADdata

Phi Geminorum, Latinized from φ Geminorum, is a binary star7 in the constellation Gemini, to the southeast of Pollux. It is visible to the naked eye with an apparent visual magnitude of 4.95.3 Based upon an annual parallax shift of 14.66 mas,2 this system is located around 220 light years from the Sun.

The two components of this system have a circular orbit with a period of 582 days.7 The primary component is an A-type main sequence star with a stellar classification of A3 V.5 It is around 600 million years old and spinning relatively rapidly with a projected rotational velocity of 16510 km/s. This rate of spin is giving the star an oblate shape with an equatorial bulge that is 6% larger than the polar radius.5 The star has nearly double the mass of the Sun and radiates 36.59 times the solar luminosity from its outer atmosphere at an effective temperature of 8,5518 K.

References

References

  1. Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters. 38 (5): 331. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015. XHIP record for this object at VizieR.
  2. van Leeuwen, F. (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, S2CID 18759600.
  3. Mermilliod, J.-C. (1986), "Compilation of Eggen's UBV data, transformed to UBV (unpublished)", Catalogue of Eggen's UBV Data, SIMBAD, Bibcode:1986EgUBV........0M.
  4. Zorec, J.; Royer, F. (1 January 2012). "Rotational velocities of A-type stars. IV. Evolution of rotational velocities". Astronomy and Astrophysics. 537: A120. arXiv:1201.2052. Bibcode:2012A&A...537A.120Z. doi:10.1051/0004-6361/201117691. ISSN 0004-6361. S2CID 55586789.
  5. van Belle, Gerard T. (March 2012), "Interferometric observations of rapidly rotating stars", The Astronomy and Astrophysics Review, 20 (1): 51, arXiv:1204.2572, Bibcode:2012A&ARv..20...51V, doi:10.1007/s00159-012-0051-2, S2CID 119273474.
  6. Wilson, R. E. (1953), "General Catalogue of Stellar Radial Velocities", Carnegie Institute Washington D.C. Publication, Carnegie Institute of Washington, D.C., Bibcode:1953GCRV..C......0W.
  7. Abt, Helmut A. (August 2005), "Observed Orbital Eccentricities", The Astrophysical Journal, 629 (1): 507–511, Bibcode:2005ApJ...629..507A, doi:10.1086/431207.
  8. David, Trevor J.; Hillenbrand, Lynne A. (2015), "The Ages of Early-Type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets", The Astrophysical Journal, 804 (2): 146, arXiv:1501.03154, Bibcode:2015ApJ...804..146D, doi:10.1088/0004-637X/804/2/146, S2CID 33401607.
  9. McDonald, I.; et al. (2012), "Fundamental Parameters and Infrared Excesses of Hipparcos Stars", Monthly Notices of the Royal Astronomical Society, 427 (1): 343–57, arXiv:1208.2037, Bibcode:2012MNRAS.427..343M, doi:10.1111/j.1365-2966.2012.21873.x, S2CID 118665352.
  10. Royer, F.; et al. (February 2007), "Rotational velocities of A-type stars. III. Velocity distributions", Astronomy and Astrophysics, 463 (2): 671–682, arXiv:astro-ph/0610785, Bibcode:2007A&A...463..671R, doi:10.1051/0004-6361:20065224, S2CID 18475298.
  11. "* phi Gem". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2016-12-08.{{cite web}}: CS1 maint: postscript (link)