4 Cygni

4 Cygni is a binary star[7] system in the northern constellation of Cygnus. It is a faintly visible to the naked eye with an apparent visual magnitude of 5.17.[2] The distance to 4 Cygni, as determined from its annual parallax shift of 5.8 mas,[1] is about 560 light years.

4 Cygni
Observation data
Epoch J2000      Equinox J2000
Constellation Cygnus
Right ascension 19h 26m 09.12787s[1]
Declination +36° 19′ 04.4369″[1]
Apparent magnitude (V) 5.17[2]
Characteristics
Evolutionary stage main sequence[3]
Spectral type B8p Si (Fe II)[4]
B−V color index −0.120±0.001[2]
Variable type α2 CVn[5]
Astrometry
Radial velocity (Rv)−22[6] km/s
Proper motion (μ) RA: +3.769[1] mas/yr
Dec.: +13.236[1] mas/yr
Parallax (π)5.8357 ± 0.1372[1] mas
Distance560 ± 10 ly
(171 ± 4 pc)
Absolute magnitude (MV)−1.51[2]
Orbit[7]
Period (P)35.0225±0.0002 d
Eccentricity (e)0.45±0.13
Periastron epoch (T)2438929.1±1.1 JD
Argument of periastron (ω)
(secondary)		290±21°
Semi-amplitude (K1)
(primary)		5.7±0.6 km/s km/s
Details[3]
Mass4.08±0.18 M☉
Radius5.03[8] R☉
Luminosity501+130
−103 L☉
Temperature12,190+399
−387 K
Rotational velocity (v sin i)30±4[9] km/s
Age145 Myr
Other designations
4 Cyg, V1741 Cygni, BD+36°3557, FK5 3554, GC 26846, HD 183056, HIP 95556, HR 7395, SAO 68301[10]
Database references
SIMBADdata

This is single-lined spectroscopic binary with an orbital period of 35 days and an eccentricity of 0.45.[7] The visible component is a B-type star with a stellar classification of B8p Si (Fe II),[4] where the suffix notation indicates this is type of chemically peculiar star known as a silicon star. It displays an overabundance of iron in the visual spectrum, while the star appears helium-weak in the ultraviolet.[4]

4 Cygni A is an Alpha2 Canum Venaticorum variable that varies by 0.02 magnitude over a period of 0.68674 days.[5] The average quadratic field strength of the magnetic field is (254.7±57.2)×10−4 T.[11] With an age of 145 million years, it has four[3] times the mass of the Sun and five[8] times the Sun's radius. It radiates around 501 times the Sun's luminosity from its photosphere at an effective temperature of 12,190 K.[3]

References
  1. 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.
  2. Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015, S2CID 119257644.
  3. Kochukhov, O.; Bagnulo, S. (2006), "Evolutionary state of magnetic chemically peculiar stars", Astronomy and Astrophysics, 450 (2): 763, arXiv:astro-ph/0601461, Bibcode:2006A&A...450..763K, doi:10.1051/0004-6361:20054596, S2CID 18596834.
  4. Jaschek, M.; Jaschek, C. (October 1980), "Ground-based observations of some stars classified in the satellite ultraviolet with spectral particularities.", Astronomy and Astrophysics Supplement Series, 42: 115–118, Bibcode:1980A&AS...42..115J.
  5. Samus, N. N.; et al. (2017), "General Catalogue of Variable Stars", Astronomy Reports, 5.1, 61 (1): 80–88, Bibcode:2017ARep...61...80S, doi:10.1134/S1063772917010085, S2CID 125853869.
  6. Wilson, Ralph Elmer (1953), "General catalogue of stellar radial velocities", Washington, Carnegie Institution of Washington: 0, Bibcode:1953GCRV..C......0W.
  7. Abt, Helmut A.; Snowden, Michael S. (February 1973), "The Binary Frequency for AP Stars", Astrophysical Journal Supplement, 25: 137, Bibcode:1973ApJS...25..137A, doi:10.1086/190265.
  8. Shulyak, D.; et al. (2014), "Interferometry of chemically peculiar stars: Theoretical predictions versus modern observing facilities", Monthly Notices of the Royal Astronomical Society, 443 (2): 1629, arXiv:1406.6093, Bibcode:2014MNRAS.443.1629S, doi:10.1093/mnras/stu1259, S2CID 96452769.
  9. Royer, F.; et al. (2002), "Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin i", Astronomy and Astrophysics, 393 (3): 897–912, arXiv:astro-ph/0205255, Bibcode:2002A&A...393..897R, doi:10.1051/0004-6361:20020943, S2CID 14070763.
  10. "4 Cyg". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-01-08.
  11. Bychkov, V. D.; et al. (2009), "Catalogue of averaged stellar effective magnetic fields - II. Re-discussion of chemically peculiar A and B stars", Monthly Notices of the Royal Astronomical Society, 394 (3): 1338, Bibcode:2009MNRAS.394.1338B, doi:10.1111/j.1365-2966.2008.14227.x.
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