Theta Cygni

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Theta Cygni A/B
Diagram showing star positions and boundaries of the Cygnus constellation and its surroundings
Cercle rouge 100%.svg

Location of θ Cygni (circled)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Cygnus
Right ascension 19h 36m 26.53436s[1]
Declination +50° 13′ 15.9646″[1]
Apparent magnitude (V) 4.490[2]/13.03[3]
Spectral type F3 V[4] + M3 V[5]
U−B color index –0.03[6]
B−V color index +0.38[6]
Radial velocity (Rv) –27.4[2] km/s
Proper motion (μ) RA: –8.87[1] mas/yr
Dec.: +262.45[1] mas/yr
Parallax (π) 54.54 ± 0.15[1] mas
Distance 59.8 ± 0.2 ly
(18.34 ± 0.05 pc)
Absolute magnitude (MV) 3.14[2]
θ Cyg A
Mass 1.38±0.05[7] M
Radius 1.58±0.002[8] R
Luminosity 4.265±0.090[9] L
Surface gravity (log g) 4.30[10] cgs
Temperature 6381±65[9] K
Metallicity [Fe/H] 0.01[10] dex
Rotational velocity (v sin i) 7[11] km/s
Age 1.3+0.6
[10] Gyr
θ Cyg B
Mass 0.33[7] M
Other designations
A: 13 Cyg, Tet Cyg, BD+49 3062 A, GJ 765 A, HD 185395, HR 7469, SAO 31815, HIP 96441, NLTT 48025.[12]
B: BD+49 3062 B, GJ 765 B, NLTT 48024.

Theta Cygni (θ Cygni, θ Cyg) is a star in the northern constellation of Cygnus. It has an apparent visual magnitude of 4.5,[2] so it can be seen from the northern hemisphere with the naked eye in sufficiently dark skies. Based upon parallax measurements, it is at a distance of about 59.8 light-years (18.3 parsecs) from the Earth.[1] It is suspected of hosting an extrasolar planet.[7]

The spectrum of this star matches a stellar classification of F3 V.[4] The luminosity class 'V' is associated with a category of stars called main sequence, which, like the Sun, are generating energy through the nuclear fusion of hydrogen at their cores. The outer envelope of this star is radiating 4.2 times the luminosity of the Sun at an effective temperature of about 6,381 K,[9] which gives it the yellow-white hue typical of F-type stars.[13] Theta Cygni is larger than the Sun, with about 38%[7] more mass and a 58%[8] greater radius. The estimated age of this star is probably in the range of 0.6–1.9 billion years.[10]

Theta Cygni has a faint companion star at an angular separation of about three arcseconds and a position angle of 56°.[14] This star has an apparent visual magnitude of 13.03,[3] which is too faint to be seen without a telescope. It is a red dwarf star with a stellar classification of M3 V[5] and an estimated mass of about 0.33 times the mass of the Sun.[7] Both components of this system are traveling together through space with a high proper motion of 0.261 arcseconds per year, or 0.4° per century.[3]

Planetary companion?[edit]

Radial velocity variations of Theta Cygni have been detected by the ELODIE team while searching of extrasolar planets. Desort et al. (2009)[7] infer these variations are not caused by a dim stellar companion roughly 80 Astronomical Units away from the star, but suggest instead the presence of a perturbing planetary object, twice as massive as Jupiter and orbiting around the primary star in less than half a year. This extrasolar planet has yet to be confirmed.

The Theta Cygni planetary system
(in order from star)
Mass Semimajor axis
Orbital period
Eccentricity Inclination Radius
b (unconfirmed) ≈2.3 MJ 0.635 154.5 0


  1. ^ a b c d e f van Leeuwen, F. (November 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 Holmberg, J.; Nordstrom, B.; Andersen, J. (July 2009), "The Geneva-Copenhagen survey of the solar neighbourhood. III. Improved distances, ages, and kinematics", Astronomy and Astrophysics, 501 (3): 941–947, arXiv:0811.3982Freely accessible, Bibcode:2009A&A...501..941H, doi:10.1051/0004-6361/200811191 
  3. ^ a b c Lépine, Sébastien; Shara, Michael M. (March 2005), "A Catalog of Northern Stars with Annual Proper Motions Larger than 0.15" (LSPM-NORTH Catalog)", The Astronomical Journal, 129 (3): 1483–1522, arXiv:astro-ph/0412070Freely accessible, Bibcode:2005AJ....129.1483L, doi:10.1086/427854 
  4. ^ a b Eggen, O. J. (1962), "Space-velocity vectors for 3483 stars with proper motion and radial velocity", Royal Observatory Bulletin, 51, Bibcode:1962RGOB...51...79E 
  5. ^ a b Haas, Michael Robert; et al. (January 2011), "Public Kepler Data on the Bright Star Theta Cygni", Bulletin of the American Astronomical Society, 43, Bibcode:2011AAS...21714007H 
  6. ^ a b Nicolet, B. (1978), "Photoelectric photometric Catalogue of homogeneous measurements in the UBV System", Astronomy and Astrophysics Supplement Series, 34: 1–49, Bibcode:1978A&AS...34....1N 
  7. ^ a b c d e f Desort, M.; et al. (November 2009), "Extrasolar planets and brown dwarfs around A-F type stars. VII. θ Cygni radial velocity variations: planets or stellar phenomenon?", Astronomy and Astrophysics, 506 (3): 1469–1476, arXiv:0908.4521Freely accessible, Bibcode:2009A&A...506.1469D, doi:10.1051/0004-6361/200911731 
  8. ^ a b Takeda, Genya; et al. (2007), "Structure and Evolution of Nearby Stars with Planets. II. Physical Properties of 1000 Cool Stars from the SPOCS Catalog", The Astrophysical Journal Supplement Series, 168 (2): 297–318, arXiv:astro-ph/0607235Freely accessible, Bibcode:2007ApJS..168..297T, doi:10.1086/509763 
  9. ^ a b c Boyajian, Tabetha S.; et al. (February 2012), "Stellar Diameters and Temperatures. I. Main-sequence A, F, and G Stars", The Astrophysical Journal, 746 (1): 101, arXiv:1112.3316Freely accessible, Bibcode:2012ApJ...746..101B, doi:10.1088/0004-637X/746/1/101 . See Table 10.
  10. ^ a b c d Cunha, Katia; et al. (February 2000), "A Uniform Analysis of Boron in F and G Disk Dwarfs fromHubble Space Telescope Archival Spectra", The Astrophysical Journal, 530 (2): 939–948, Bibcode:2000ApJ...530..939C, doi:10.1086/308415 
  11. ^ Bernacca, P. L.; Perinotto, M. (1970), "A catalogue of stellar rotational velocities", Contributi Osservatorio Astronomico di Padova in Asiago, 239 (1), Bibcode:1970CoAsi.239....1B 
  12. ^ "LTT 15729 -- High proper-motion Star", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2012-01-15 
  13. ^ "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, retrieved 2012-01-16 
  14. ^ van Biesbroeck, G. (November 1974), "Micrometric Measures of Double Stars", Astrophysical Journal Supplement, 28: 413, Bibcode:1974ApJS...28..413V, doi:10.1086/190327  Listed as ADS 12695.