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16 Cygni

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16 Cygni
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Cygnus
16 Cygni A
Right ascension 19h 41m 48.95s[1]
Declination +50° 31′ 30.2″[1]
Apparent magnitude (V) 5.96
16 Cygni B
Right ascension 19h 41m 51.97s[1]
Declination +50° 31′ 03.1″[1]
Apparent magnitude (V) 6.20
Spectral type G1.5Vb / G2.5Vb / M?V
U−B color index 0.19 / 0.20
B−V color index 0.64 / 0.66
Variable type None
16 Cyg A
Proper motion (μ) RA: −147.82 ± 0.30[1] mas/yr
Dec.: −159.01 ± 0.28[1] mas/yr
Parallax (π) 47.44 ± 0.27[1] mas
Distance 68.8 ± 0.4 ly
(21.1 ± 0.1 pc)
Absolute magnitude (MV) 4.29
16 Cyg B
Proper motion (μ) RA: 135.11 mas/yr
Dec.: −163.78 mas/yr
Parallax (π) 47.14 ± 0.27[1] mas
Distance 69.2 ± 0.4 ly
(21.2 ± 0.1 pc)
Absolute magnitude (MV) 4.53
16 Cyg A
Mass 1.02 M
Radius 1.7 R
Luminosity 1.6 L
Temperature 5,803 ± 3.1[2] K
Metallicity 114%Sun
Rotation 26.9
Age 10.4 Gyr
16 Cyg B
Mass 0.97 M
Radius 1.2 R
Luminosity 1.3 L
Temperature 5,752 ± 3.5[2] K
Metallicity 123% Sun
Rotation 29.1
Age 9.9 Gyr
Other designations
16 Cygni A
BD+50 2847, GCTP 4634.00, GJ 765.1 A, HD 186408, HIP 96895, HR 7503, LTT 15750, SAO 31898, Struve 4046A
16 Cygni B
BD+50 2848, GJ 765.1 B, HD 186427, HIP 96901, HR 7504, LTT 15751, SAO 31899, Struve 4046B, KIC 12069449
Database references
A data2
B data3
Extrasolar Planets

16 Cygni or 16 Cyg is the Flamsteed designation of a triple star system approximately 69 light-years away from Earth in the constellation of Cygnus. It consists of two Sun-like yellow dwarf stars, 16 Cygni A and 16 Cygni B, together with a red dwarf, 16 Cygni C. In 1996 an extrasolar planet was discovered in an eccentric orbit around 16 Cygni B.


The parallax of the two brightest stars were measured as part of the Hipparcos astrometry mission. This yielded a parallax of 47.44 milliarcseconds for 16 Cygni A[1] and 47.14 milliarcseconds for 16 Cygni B.[1] Since the two components are associated, it is reasonable to assume they lie at the same distance, so the different parallaxes are a result of experimental error (indeed, when the associated parallax errors are taken into account, the ranges of the parallaxes overlap). Using the parallax of the A component, the distance is 21.1 parsecs. The parallax of the B component corresponds to a distance of 21.2 parsecs.

Stellar components[edit]

16 Cygni is a hierarchal triple system. Stars A and C form a close binary with a projected separation of 73 AU.[3] The orbital elements of the A–C binary are currently unknown. At a distance of 860 AU from A is a third component designated 16 Cygni B. The orbit of B relative to the A–C pair was determined in 1999 and not updated since (as of June 2007): plausible orbits range in period from 18,200 to 1.3 million years, with a semimajor axis ranging from 877 to 15,180 AU. In addition B orbits between 100 and 160 degrees inclination, that is against the A–C pole such that 90 degrees would be ecliptical.[4]

Both 16 Cygni A and 16 Cygni B are yellow dwarf stars like the Sun. According to data from the Geneva–Copenhagen survey, both stars have masses similar to the Sun.[5][6] Age estimates for the two stars vary slightly, but 16 Cygni is likely to be much older than the Solar System, at around 10,000 million years old. 16 Cygni C is much fainter than either of these stars, and may be a red dwarf.[3]

Planetary system[edit]

The 16 Cygni planetary system[7]
(in order from star)
Mass Semimajor axis
Orbital period
Eccentricity Inclination Radius
b 2.38 ± 0.04 MJ 1.693 799.5 0.689 ± 0.011

In 1996 an extrasolar planet in an eccentric orbit was announced around the star 16 Cygni B.[8] The planet's orbit takes 798.5 days to complete, with a semimajor axis of 1.68 AU.[9]

Like the majority of extrasolar planets detectable from Earth, 16 Cygni Bb was deduced from the radial velocity of its parent star. At the time that only gave a lower limit on the mass: in this case, about 1.68 times that of Jupiter. In 2012, two astronomers, E. Plavalova and N.A. Solovaya, showed that the stable orbit would demand about 2.38 Jupiter masses, such that its orbit was inclined at either 45° or 135°.[7]

The eccentric orbit and mass of 16 Cygni Bb makes it extremely unlikely that a terrestrial sized planet will be found orbiting within the star's habitable zone,[10]

For the 16 Cyg B system, only particles inside approximately 0.3 AU remained stable within a million years of formation, leaving open the possibility of short-period planets. For them, observation rules out any such planet of over a Neptune mass.[11]

There was a METI message sent to the 16 Cygni system. It was transmitted from Eurasia's largest radar—the 70-meter (230-foot) Eupatoria Planetary Radar. The message was named Cosmic Call 1; it was sent on May 24, 1999, and it will reach 16 Cygni in November 2069.[12]

The 16 Cygni system is within the field of view of the Kepler space telescope.

See also[edit]


  1. ^ a b c d e f g h i j van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. Bibcode:2007A&A...474..653V. arXiv:0708.1752Freely accessible. doi:10.1051/0004-6361:20078357.  Vizier catalog entry for A Vizier catalog entry for B
  2. ^ a b Kovtyukh; Soubiran, C.; Belik, S. I.; Gorlova, N. I.; et al. (2003). "High precision effective temperatures for 181 F-K dwarfs from line-depth ratios". Astronomy and Astrophysics. 411 (3): 559–564. Bibcode:2003A&A...411..559K. arXiv:astro-ph/0308429Freely accessible. doi:10.1051/0004-6361:20031378. 
  3. ^ a b Raghavan; Henry, Todd J.; Mason, Brian D.; Subasavage, John P.; Jao, Wei‐Chun; Beaulieu, Thom D.; Hambly, Nigel C.; et al. (2006). "Two Suns in The Sky: Stellar Multiplicity in Exoplanet Systems". The Astrophysical Journal. 646 (1): 523–542. Bibcode:2006ApJ...646..523R. arXiv:astro-ph/0603836Freely accessible. doi:10.1086/504823. 
  4. ^ Hauser, H.; Marcy, G. (1999). "The Orbit of 16 Cygni AB". Publications of the Astronomical Society of the Pacific. 111 (757): 321–334. Bibcode:1999PASP..111..321H. doi:10.1086/316328. 
  5. ^ Holmberg; et al. (2007). "Record 13627". Geneva-Copenhagen Survey of Solar neighbourhood. Retrieved 19 November 2008. 
  6. ^ Holmberg; et al. (2007). "Record 13631". Geneva-Copenhagen Survey of Solar neighbourhood. Retrieved 19 November 2008. 
  7. ^ a b E. Plávalová; N. A. Solovaya (2012). "Analysis of the motion of an extrasolar planet in a binary system". Astronomy & Astrophysics. 146: 108. Bibcode:2013AJ....146..108P. arXiv:1212.3843Freely accessible. doi:10.1088/0004-6256/146/5/108. 
  8. ^ Cochran; Hatzes, Artie P.; Butler, R. Paul; Marcy, Geoffrey W.; et al. (1997). "The Discovery of a Planetary Companion to 16 Cygni B". The Astrophysical Journal. 483 (1): 457–463. Bibcode:1997ApJ...483..457C. arXiv:astro-ph/9611230Freely accessible. doi:10.1086/304245. 
  9. ^ Butler; Wright, J. T.; Marcy, G. W.; Fischer, D. A.; Vogt, S. S.; Tinney, C. G.; Jones, H. R. A.; Carter, B. D.; Johnson, J. A.; McCarthy, C.; Penny, A.J.; et al. (2006). "Catalog of Nearby Exoplanets". The Astrophysical Journal. 646 (1): 505–522. Bibcode:2006ApJ...646..505B. arXiv:astro-ph/0607493Freely accessible. doi:10.1086/504701. 
  10. ^ Wittenmyer, R. A.; Endl, M.; Cochran, W. D.; Levison, H. F. (2007). "Dynamical and Observational Constraints on Additional Planets in Highly Eccentric Planetary Systems". The Astronomical Journal. 134 (3): 1276–1284. Bibcode:2007AJ....134.1276W. arXiv:0706.1962Freely accessible. doi:10.1086/520880. 
  11. ^ Wittenmyer; Endl, Michael; Cochran, William D.; Levison, Harold F.; et al. (2007). "Dynamical and Observational Constraints on Additional Planets in Highly Eccentric Planetary Systems". The Astronomical Journal. 134 (3): 1276–1284. Bibcode:2007AJ....134.1276W. arXiv:0706.1962Freely accessible. doi:10.1086/520880. 
  12. ^ (in Russian)

External links[edit]

Coordinates: Sky map 19h 41m 51.9720s, +50° 31′ 03.083″