Theta Cygni

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θ Cygni
Cygnus constellation map.svg
Red circle.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
Distance59.8 ± 0.2 ly
(18.34 ± 0.05 pc)
Absolute magnitude (MV)3.14[2]
θ Cyg A
Mass1.35 - 1.39[7] M
Radius1.49±0.002[7] R
Luminosity4.265±0.090[8] L
Surface gravity (log g)4.23±0.03[7] cgs
Temperature6697±78[7] K
Metallicity [Fe/H]−0.02±0.06[7] dex
Rotational velocity (v sin i)7[9] km/s
Age1.0 - 1.6[7] Gyr
θ Cyg B
Mass0.35[10] M
Radius0.36[7] R
Luminosity0.01[7] L
Temperature3,000 - 3,500[7] K
GSC 03564-00642
Radius0.28[7] R
Luminosity0.013[7] L
Temperature3,700[7] K
Other designations
13 Cyg, θ Cyg, BD+49 3062, GJ 765, HD 185395, HR 7469, SAO 31815, HIP 96441
B: 2MASS 19362771+5013419, KIC 11918644
GJ 765B: 2MASS 19362286+5013034, KIC 11918614
GSC 03564-00642: 2MASS J19361440+5013096, KIC 11918550
Database references
θ Cygni B
θ Cygni C
θ Cygni D
GJ 765B
GSC 03564-00642

Theta Cygni (θ Cygni, θ Cyg) is a star in the northern constellation of Cygnus. It has an apparent visual magnitude of 4.5, 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. It is suspected of hosting an extrasolar planet.


The spectrum of the primary 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,[8] which gives it the yellow-white hue typical of F-type stars.[11] Theta Cygni is larger than the Sun, with about 38%[10] more mass and a 58%[12] greater radius. The estimated age of this star is probably in the range of 0.6–1.9 billion years.[13]


θ Cygni has several faint companions. The closest is θ Cygni B, a 13th magnitude red dwarf around 3" distant, and believed to be in orbit around 46 AU from θ Cygni. A 12th magnitude star around an arc minute distant is catalogued as component C and is believed to be an optical companion. Component D is a magnitude 12.5 star also thought to be an optical companion. GJ 765B, not to be confused with θ Cygni B, is 13th magnitude and a possible subdwarf companion. GSC 03564-00642 is another 13th magnitude red dwarf and thought to be a common proper montion companion to θ Cygni.[7]

θ Cygni B has an apparent visual magnitude of 13.03,[3] which is too faint to be seen without a telescope. It has a stellar classification of M3 V[5] and an estimated mass of about 0.33 times the mass of the Sun.[10] θ Cygni A and B are traveling together through space with a high proper motion of 0.261 arcseconds per year, or 0.4° per century.[3] It is possible that θ Cygni B is itself a close binary containing two red dwarfs, each of which would be fainter and less massive than calculated for a single star.[7]

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)[10] 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 roughly 150 days.[10] This extrasolar planet has yet to be confirmed. Observations made at Lick Observatory show evidence for radial velocity variation at this period as well as at yearly aliases, however these signals have not reached statistical significance.[14]

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 van Leeuwen, F. (November 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. ^ a b c 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:0811.3982, 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/0412070, 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: 79, 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: 140.07, 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 g h i j k l m n Guzik, J. A.; et al. (2016). "Detection of Solar-like Oscillations, Observational Constraints, and Stellar Models for θ Cyg, the Brightest Star Observed by the Kepler Mission". The Astrophysical Journal. 831 (1). 17. arXiv:1607.01035. Bibcode:2016ApJ...831...17G. doi:10.3847/0004-637X/831/1/17.
  8. ^ a b 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:1112.3316, Bibcode:2012ApJ...746..101B, doi:10.1088/0004-637X/746/1/101. See Table 10.
  9. ^ Bernacca, P. L.; Perinotto, M. (1970), "A catalogue of stellar rotational velocities", Contributi Osservatorio Astronomico di Padova in Asiago, 239 (1): 1, Bibcode:1970CoAsi.239....1B
  10. ^ a b c d e 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:0908.4521, Bibcode:2009A&A...506.1469D, doi:10.1051/0004-6361/200911731
  11. ^ "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, retrieved 2012-01-16
  12. ^ 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/0607235, Bibcode:2007ApJS..168..297T, doi:10.1086/509763
  13. ^ 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
  14. ^ Howard, Andrew W.; Fulton, Benjamin J. (2016). "Limits on Planetary Companions from Doppler Surveys of Nearby Stars". Publications of the Astronomical Society of the Pacific. 128 (969). 114401. arXiv:1606.03134. Bibcode:2016PASP..128k4401H. doi:10.1088/1538-3873/128/969/114401.