16 Cygni

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.

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
Characteristics
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
Astrometry
16 Cyg A
Proper motion (μ) RA: −148.299±0.063[2] mas/yr
Dec.: −158.961±0.070[2] mas/yr
Parallax (π)47.2771 ± 0.0327[2] mas
Distance68.99 ± 0.05 ly
(21.15 ± 0.01 pc)
Absolute magnitude (MV)4.29
16 Cyg B
Proper motion (μ) RA: −134.791±0.049[3] mas/yr
Dec.: −162.493±0.045[3] mas/yr
Parallax (π)47.2754 ± 0.0245[3] mas
Distance68.99 ± 0.04 ly
(21.15 ± 0.01 pc)
Absolute magnitude (MV)4.53
Details
16 Cyg A
Mass1.08±0.02[4] M☉
Radius1.229±0.008[4] R☉
Luminosity1.55±0.07[4] L☉
Surface gravity (log g)4.292±0.003[4] cgs
Temperature5,830 ± 11[5] K
Metallicity [Fe/H]0.101 ± 0.008[5] dex
Rotation23.8+1.5
−1.8 d[6]
Rotational velocity (v sin i)2.23 ± 0.07[6] km/s
Age7.07±0.26[4] Gyr
16 Cyg B
Mass1.04±0.02[4] M☉
Radius1.116±0.006[4] R☉
Luminosity1.25±0.05[4] L☉
Surface gravity (log g)4.359±0.002[4] cgs
Temperature5,751 ± 11[5] K
Metallicity [Fe/H]0.054 ± 0.008[5] dex
Rotation23.2+11.5
−3.2 d[6]
Rotational velocity (v sin i)1.35 ± 0.08[6] km/s
Age6.74±0.24[4] 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
SIMBADdata
A data2
B data3
Extrasolar Planets
Encyclopaedia		data

Distance

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
16 Cygni in optical light

16 Cygni is a hierarchical triple system. Stars A and C form a close binary with a projected separation of 73 AU.[7] 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.[8]

Both 16 Cygni A and 16 Cygni B are yellow dwarf stars similar to the Sun. Their spectral types have been given as G1.5V and G3V,[9] with A being a little hotter than the Sun, and B somewhat cooler. The system was within the field of view of the original mission of the Kepler spacecraft, which collected extremely precise photometric data of the stars. From these measurements, asteroseismology models have calculated precise masses of 1.08 and 1.04 times the solar mass for 16 Cygni A and 16 Cygni B respectively, and independent ages of around 7 billion years for each star.[4] The system has also been observed through interferometry, which allowed the determination of the angular diameter of each star.[10] The angular diameters together with the asteroseismology models were used to calculate radii of 1.229 and 1.116 times the solar radius for components A and B respectively.[4]

Abundances

Despite having the same age and presumably the same primordial composition, observations show a small difference in the metallicity of the two 16 Cygni stars. The primary star has an iron abundance of 1.26 times the solar value, compared to 1.13 for the secondary star. A similar trend has been found for all other metals, with the primary component having an average of 10% more metals than B. One possibility is that this difference is linked to the planet 16 Cygni Bb, since its formation may have removed metals from the protoplanetary disk around 16 Cygni B.[11][5] However, another study found no difference in heavy element abundances between 16 Cygni A and B.[12]

Another chemical peculiarity between the stars is in their lithium abundance. Measurements of the lithium abundance in the system show a 4 times higher abundance in component A than in 16 Cygni B. Compared to the Sun, 16 Cygni A has 1.66 as much lithium, while 16 Cygni B has only 0.35.[13] It has been hypothesized that the accretion of about 1 Earth mass of metals by 16 Cygni B soon after the system's formation may have destroyed the lithium in the star's atmosphere.[13] Another proposed scenario is the engulfment of a Jupiter-mass planet by 16 Cygni A, which increased the amount of lithium in the star's outer atmosphere.[14]

Planetary system

In 1996 an extrasolar planet in an eccentric orbit was announced around the star 16 Cygni B. The discovery by the radial velocity method was made from independent observations from the McDonald Observatory and Lick Observatory.[15][16] The planet's orbit takes 799.5 days to complete, with a semimajor axis of 1.69 AU.[17] It has a very high eccentricity of 0.69, which might be the result of gravitational perturbations from 16 Cygni A. In particular, simulations show the planet's eccentricity oscillates between low and high values in timescales of tens of millions of years.[18][19]

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°.[17]

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.[20]

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.[20]

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.[21]

The 16 Cygni planetary system[17]
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination Radius
b 2.38 ± 0.04 MJ 1.693 799.5 0.689 ± 0.011 — —

See also

References
  1. 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. Vizier catalog entry for A Vizier catalog entry for B
  2. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  3. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  4. Metcalfe, Travis S.; Creevey, Orlagh L.; Davies, Guy R. (2015). "Asteroseismic Modeling of 16 Cyg A & B using the Complete Kepler Data Set". The Astrophysical Journal Letters. 811 (2). L37. arXiv:1508.00946. Bibcode:2015ApJ...811L..37M. doi:10.1088/2041-8205/811/2/L37.
  5. Tucci Maia, Marcelo; Meléndez, Jorge; Ramírez, Iván (2014). "High Precision Abundances in the 16 Cyg Binary System: A Signature of the Rocky Core in the Giant Planet". The Astrophysical Journal. 790 (2): L25. arXiv:1407.4132. Bibcode:2014ApJ...790L..25T. doi:10.1088/2041-8205/790/2/L25. S2CID 118403440.
  6. Davies, G. R; Chaplin, W. J; Farr, W. M; García, R. A; Lund, M. N; Mathis, S; Metcalfe, T. S; Appourchaux, T; Basu, S; Benomar, O; Campante, T. L; Ceillier, T; Elsworth, Y; Handberg, R; Salabert, D; Stello, D (2015). "Asteroseismic inference on rotation, gyrochronology and planetary system dynamics of 16 Cygni". Monthly Notices of the Royal Astronomical Society. 446 (3): 2959. arXiv:1411.1359. Bibcode:2015MNRAS.446.2959D. doi:10.1093/mnras/stu2331. S2CID 119110862.
  7. 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. arXiv:astro-ph/0603836. Bibcode:2006ApJ...646..523R. doi:10.1086/504823. S2CID 5669768.
  8. 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.
  9. Gray, R. O; Corbally, C. J; Garrison, R. F; McFadden, M. T; Robinson, P. E (2003), "Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 Parsecs: The Northern Sample. I", The Astronomical Journal, 126 (4): 2048, arXiv:astro-ph/0308182, Bibcode:2003AJ....126.2048G, doi:10.1086/378365, S2CID 119417105
  10. White, T. R; Huber, D; Maestro, V; Bedding, T. R; Ireland, M. J; Baron, F; Boyajian, T. S; Che, X; Monnier, J. D; Pope, B. J. S; Roettenbacher, R. M; Stello, D; Tuthill, P. G; Farrington, C. D; Goldfinger, P. J; McAlister, H. A; Schaefer, G. H; Sturmann, J; Sturmann, L; Ten Brummelaar, T. A; Turner, N. H (2013). "Interferometric radii of bright Kepler stars with the CHARA Array: θ Cygni and 16 Cygni a and B". Monthly Notices of the Royal Astronomical Society. 433 (2): 1262. arXiv:1305.1934. Bibcode:2013MNRAS.433.1262W. doi:10.1093/mnras/stt802. S2CID 8165381.
  11. Ramírez, I; Meléndez, J; Cornejo, D; Roederer, I. U; Fish, J. R (2011). "Elemental Abundance Differences in the 16 Cygni Binary System: A Signature of Gas Giant Planet Formation?". The Astrophysical Journal. 740 (2): 76. arXiv:1107.5814. Bibcode:2011ApJ...740...76R. doi:10.1088/0004-637X/740/2/76. S2CID 119257511.
  12. Schuler, Simon C; Cunha, Katia; Smith, Verne V; Ghezzi, Luan; King, Jeremy R; Deliyannis, Constantine P; Boesgaard, Ann Merchant (2011). "Detailed Abundances of the Solar Twins 16 Cygni a and B: Constraining Planet Formation Models". The Astrophysical Journal. 737 (2): L32. arXiv:1107.3183. Bibcode:2011ApJ...737L..32S. doi:10.1088/2041-8205/737/2/L32.
  13. Deal, Morgan; Richard, Olivier; Vauclair, Sylvie (1 December 2015). "Accretion of planetary matter and the lithium problem in the 16 Cygni stellar system". Astronomy & Astrophysics. 584: A105. arXiv:1509.06958. Bibcode:2015A&A...584A.105D. doi:10.1051/0004-6361/201526917. S2CID 119293969.
  14. Carlos, Marília; et al. (March 2016), "Correlation between lithium abundances and ages of solar twin stars", Astronomy & Astrophysics, 587 (100): 6, arXiv:1601.05054, Bibcode:2016A&A...587A.100C, doi:10.1051/0004-6361/201527478, S2CID 119268561, A100.
  15. Cochran, W. D; Hatzes, A. P; Butler, R. P; Marcy, G. W (1996), "Detection of a planetary companion to 16 Cygni B", AAA/Division for Planetary Sciences Meeting Abstracts #28, 28: 12.04, Bibcode:1996DPS....28.1204C
  16. Cochran, William D.; et al. (1997). "The Discovery of a Planetary Companion to 16 Cygni B". The Astrophysical Journal. 483 (1): 457–463. arXiv:astro-ph/9611230. Bibcode:1997ApJ...483..457C. doi:10.1086/304245.
  17. Plávalová, Eva; Solovaya, Nina A. (2013). "Analysis of the motion of an extrasolar planet in a binary system". The Astronomical Journal. 146 (5): 108. arXiv:1212.3843. Bibcode:2013AJ....146..108P. doi:10.1088/0004-6256/146/5/108.
  18. Holman, Matthew; Touma, Jihad; Tremaine, Scott (1997). "Chaotic variations in the eccentricity of the planet orbiting 16 Cygni B". Nature. 386 (6622): 254. Bibcode:1997Natur.386..254H. doi:10.1038/386254a0. S2CID 4312547.
  19. Mazeh, Tsevi; Krymolowski, Yuval; Rosenfeld, Gady (1997). "The High Eccentricity of the Planet Orbiting 16 Cygni B". The Astrophysical Journal. 477 (2): L103. arXiv:astro-ph/9611135. Bibcode:1997ApJ...477L.103M. doi:10.1086/310536. S2CID 15736587.
  20. Wittenmyer, R. A.; et al. (2007). "Dynamical and Observational Constraints on Additional Planets in Highly Eccentric Planetary Systems". The Astronomical Journal. 134 (3): 1276–1284. arXiv:0706.1962. Bibcode:2007AJ....134.1276W. doi:10.1086/520880.
  21. (in Russian) http://www.cplire.ru/rus/ra&sr/VAK-2004.html

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