57 Cygni

57 Cygni is a close binary star[4] system in the constellation Cygnus, located about 530 light years from Earth. It is visible to the naked eye as a blue-white hued star with a baseline apparent visual magnitude of 4.80.[2] The pair have a magnitude difference of 0.34.[4] This system is moving closer to the Earth with a heliocentric radial velocity of −21 km/s.[2]

57 Cygni
Observation data
Epoch J2000      Equinox J2000
Constellation Cygnus
Right ascension  20h 53m 14.75503s[1]
Declination +44° 23′ 14.1408″[1]
Apparent magnitude (V) 4.80[2]
Characteristics
Spectral type B5 V[3]
B−V color index −0.134±0.006[2]
Astrometry
Radial velocity (Rv)−21.1±2.8[2] km/s
Proper motion (μ) RA: +11.94[1] mas/yr
Dec.: −2.08[1] mas/yr
Parallax (π)6.21 ± 0.22[1] mas
Distance530 ± 20 ly
(161 ± 6 pc)
Absolute magnitude (MV)−1.23[2]
Orbit[4]
Period (P)2.8548 days
Eccentricity (e)0.139±0.014[5]
Inclination (i)≈ 48[6]°
Periastron epoch (T)2441571.275 JD
Argument of periastron (ω)
(secondary)		159.6°
Semi-amplitude (K1)
(primary)		111.9 km/s
Semi-amplitude (K2)
(secondary)		126.0 km/s
Details
57 Cyg A
Mass5.54±0.55[5] M☉
Radius3.3±0.4[4] R☉
Temperature17,190[7] K
Rotational velocity (v sin i)40[8] km/s
57 Cyg B
Mass4.92±0.49[5] M☉
Radius2.9±0.4[4] R☉
Rotational velocity (v sin i)30[8] km/s
Other designations
57 Cyg, BD+43°3755, HD 199081, HIP 103089, HR 8001, SAO 50180[9]
Database references
SIMBADdata

This is a double-lined spectroscopic binary with an orbital period of 2.85 days and an eccentricity of 0.15.[4] They show a steady change in their longitude of periastron, showing an apsidal period of 203±4 years.[10] The system does not form an eclipsing binary, having the orbital inclination of around 48°.[6] Both components are B-type main-sequence stars with a stellar classification of B5 V.[4]

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.
  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.
  3. Lesh, Janet Rountree (December 1968), "The Kinematics of the Gould Belt: an Expanding Group?", Astrophysical Journal Supplement, 17: 371, Bibcode:1968ApJS...17..371L, doi:10.1086/190179.
  4. Hilditch, R. W. (1973), "The binary system 57 Cygni - apsidal motion and effects of spectral line blending", Monthly Notices of the Royal Astronomical Society, 164: 101–110, Bibcode:1973MNRAS.164..101H, doi:10.1093/mnras/164.2.101.
  5. De Laurentis, M.; et al. (August 2012), "Testing gravitational theories using eccentric eclipsing detached binaries", Monthly Notices of the Royal Astronomical Society, 424 (3): 2371–2379, arXiv:1207.5410, Bibcode:2012MNRAS.424.2371D, doi:10.1111/j.1365-2966.2012.21410.x.
  6. Jetsu, L.; et al. (November 1999), "Photometry of V 1794 Cygni between 1975 and 1995", Astronomy and Astrophysics Supplement, 139: 513–523, Bibcode:1999A&AS..139..513J, doi:10.1051/aas:1999397.
  7. Zorec, J.; et al. (July 2009), "Fundamental parameters of B supergiants from the BCD system. I. Calibration of the (λ1, D) parameters into Teff", Astronomy and Astrophysics, 501 (1): 297–320, arXiv:0903.5134, Bibcode:2009A&A...501..297Z, doi:10.1051/0004-6361/200811147.
  8. Abt, Helmut A.; et al. (July 2002), "Rotational Velocities of B Stars", The Astrophysical Journal, 573 (1): 359–365, Bibcode:2002ApJ...573..359A, doi:10.1086/340590
  9. "57 Cyg". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 16 January 2019.
  10. Tapia, M.; Smith, R. C. (November 1979), "On the spectroscopic binary 57 Cygni", Monthly Notices of the Royal Astronomical Society, 189: 551–561, Bibcode:1979MNRAS.189..551T, doi:10.1093/mnras/189.3.551.
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