Theta Geminorum

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θ Geminorum
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Gemini
Right ascension 06h 52m 47.33887s[1]
Declination +33° 57′ 40.5175″[1]
Apparent magnitude (V) 3.59[2]
Spectral type A2 IV[3]
U−B color index +0.13[2]
B−V color index +0.10[2]
Radial velocity (Rv) +21[4] km/s
Proper motion (μ) RA: −1.66[1] mas/yr
Dec.: −47.31[1] mas/yr
Parallax (π) 17.25 ± 0.19[1] mas
Distance 189 ± 2 ly
(58.0 ± 0.6 pc)
Mass 1.80[5] M
Radius 5.1[6] R
Luminosity 93[7] L
Surface gravity (log g) 3.40±0.14[5] cgs
Temperature 8,502±289[5] K
Rotational velocity (v sin i) 133[8] km/s
Age 252[5] Myr
Other designations
θ Gem, 34 Geminorum, BD+34°1481, FK5 261, HD 50019, HIP 33018, HR 2540, SAO 59570.[9]

Theta Geminorum (θ Gem, θ Geminorum) is a single[10] star in the northern zodiac constellation of Gemini. It is visual to the naked eye with an apparent visual magnitude of 3.59.[2] Based upon an annual parallax shift of 17.25 mas,[1] it is about 189 light years distant from the Sun.

This is an evolving A-type subgiant star with a stellar classification of A2 IV.[3] It has 1.80[5] times the mass of the Sun and radiates 93[7] times the solar luminosity. The measured angular diameter is 0.82±0.03 mas.[11] At an estimated distance of this star, this yields a physical size of about 5.1 times the radius of the Sun.[6] It is around 252 million years old and has a projected rotational velocity of 133[8] km/s. This rotation rate is giving the star an oblate shape, with an equatorial bulge that is 11% larger than the polar radius.[12]

The Washington Visual Double Star Catalog lists five visual companions within 100; the closest and brightest such companion is the magnitude 8.6 θ Geminorum E at an angular separation of 2.4″ along a position angle of 295°, as of 2010.[13]


  1. ^ a b c d e f van Leeuwen, F. (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. ^ a b c d Mermilliod, J.-C. (1986), "Compilation of Eggen's UBV data, transformed to UBV (unpublished)", Catalogue of Eggen's UBV data, SIMBAD, Bibcode:1986EgUBV........0M. 
  3. ^ a b Abt, Helmut A.; Morrell, Nidia I. (1995), "The Relation between Rotational Velocities and Spectral Peculiarities among A-Type Stars", Astrophysical Journal Supplement, 99: 135, Bibcode:1995ApJS...99..135A, doi:10.1086/192182. 
  4. ^ Evans, D. S. (June 20–24, 1966), "The Revision of the General Catalogue of Radial Velocities", in Batten, Alan Henry; Heard, John Frederick, Determination of Radial Velocities and their Applications, Proceedings from IAU Symposium no. 30, University of Toronto: International Astronomical Union, Bibcode:1967IAUS...30...57E. 
  5. ^ a b c d e 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:1501.03154Freely accessible, Bibcode:2015ApJ...804..146D, doi:10.1088/0004-637X/804/2/146. 
  6. ^ a b Lang, Kenneth R. (2006), Astrophysical formulae, Astronomy and astrophysics library, 1 (3rd ed.), Birkhäuser, ISBN 3-540-29692-1 . The radius (R*) is given by:
  7. ^ a b 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:1208.2037Freely accessible, Bibcode:2012MNRAS.427..343M, doi:10.1111/j.1365-2966.2012.21873.x. 
  8. ^ a b Royer, F.; et al. (October 2012), "Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin i", Astronomy and Astrophysics, 393: 897−911, arXiv:astro-ph/0205255Freely accessible, Bibcode:2002A&A...393..897R, doi:10.1051/0004-6361:20020943. 
  9. ^ "tet Gem -- Star", SIMBAD Astronomical Database, Centre de Données astronomiques de Strasbourg, retrieved 2016-12-02. 
  10. ^ Eggleton, P. P.; Tokovinin, A. A. (September 2008), "A catalogue of multiplicity among bright stellar systems", Monthly Notices of the Royal Astronomical Society, 389 (2): 869–879, arXiv:0806.2878Freely accessible, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x. 
  11. ^ Richichi, A.; et al. (February 2005), "CHARM2: An updated Catalog of High Angular Resolution Measurements", Astronomy and Astrophysics, 431 (2): 773–777, Bibcode:2005A&A...431..773R, doi:10.1051/0004-6361:20042039. 
  12. ^ van Belle, Gerard T., Gerard T. (March 2012), "Interferometric observations of rapidly rotating stars", The Astronomy and Astrophysics Review, 20 (1): 51, arXiv:1204.2572Freely accessible, Bibcode:2012A&ARv..20...51V, doi:10.1007/s00159-012-0051-2. 
  13. ^ Mason, B. D.; et al. (2014), The Washington Visual Double Star Catalog, Bibcode:2001AJ....122.3466M, doi:10.1086/323920.