Pi2 Cygni

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For other stars with this Bayer designation, see π Cygni.
Pi2 Cygni
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Cygnus
Right ascension 21h 46m 47.60832s[1]
Declination +49° 18′ 34.4511″[1]
Apparent magnitude (V) 4.24[2]
Spectral type B2.5 III[3]
U−B color index −0.79[2]
B−V color index −0.125[2]
Variable type β Cep[4]
Radial velocity (Rv) −12.3[5] km/s
Proper motion (μ) RA: +2.77[1] mas/yr
Dec.: −2.00[1] mas/yr
Parallax (π) 2.95 ± 0.34[1] mas
Distance approx. 1,100 ly
(approx. 340 pc)
Period (P) 72.0162 d
Eccentricity (e) 0.34
Periastron epoch (T) 2428410.6 JD
Argument of periastron (ω)
Semi-amplitude (K1)
7.8 km/s
π2 Cyg A
Mass 8.4±0.4[7] M
Radius 7.1[8] R
Luminosity (bolometric) 8,442[9] L
Surface gravity (log g) 3.69±0.16[10] cgs
Temperature 20,815±1,057[10] K
Metallicity [Fe/H] 0.04±0.09[10] dex
Rotational velocity (v sin i) 50±5[4] km/s
Age 33.2±5.8[7] Myr
Other designations
π2 Cyg, 81 Cygni, BD+48° 3504, FK5 821, HD 207330, HIP 107533, HR 8335, SAO 51293.[11]
Database references

Pi2 Cygni2 Cyg, π2 Cygni) is a triple star[12] system in the northern constellation of Cygnus. It is visible to the naked eye about 2.5° east-northeast of the open cluster M39,[13] having an apparent visual magnitude of 4.24.[2] Based upon an annual parallax shift of 2.95 mas,[1] it is located at a distance of roughly 1,100 light years from the Sun.

The inner pair of stars in this system form a single-lined[14] spectroscopic binary with an orbital period of 72.0162 days and an eccentricity of 0.34.[6] The primary, component A, is a B-type giant star with a stellar classification of B2.5 III.[3] It is a Beta Cephei variable[4] with an estimated 8.4[7] times the mass of the Sun and around 7.1[8] times the Sun's radius. The star is roughly 33[7] million years old and is spinning with a projected rotational velocity of 50[4] km/s. It is radiating 8,442[9] times the solar luminosity from its outer atmosphere at an effective temperature of around 20,815[10] K.

The third member of this system is a magnitude 5.98 star at an angular separation of 0.10 arc seconds along a position angle of 129°, as of 1996.[15]

Historical names[edit]

In Chinese, 螣蛇 (Téng Shé), meaning Flying Serpent, refers to an asterism consisting of π2 Cygni, α Lacertae, 4 Lacertae, π1 Cygni, HD 206267, ε Cephei, β Lacertae, σ Cassiopeiae, ρ Cassiopeiae, τ Cassiopeiae, AR Cassiopeiae, 9 Lacertae, 3 Andromedae, 7 Andromedae, 8 Andromedae, λ Andromedae, κ Andromedae, ψ Andromedae and ι Andromedae. Consequently, π2 Cygni itself is known as 螣蛇三 (Téng Shé sān, English: the Third Star of Flying Serpent)[16]


  1. ^ a b c d e f van Leeuwen, F. (2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752Freely accessible, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357. 
  2. ^ a b c d Mermilliod, J.-C. (1986), "Compilation of Eggen's UBV data, transformed to UBV (unpublished)", Catalogue of Eggen's UBV data, SIMBAD, Bibcode:1986EgUBV........0M. 
  3. ^ a b Walborn, N. R. (1971), "Some Spectroscopic Characteristics of the OB Stars: An Investigation of the Space Distribution of Certain OB Stars and the Reference Frame of the Classification", The Astrophysical Journal Supplement Series, 23: 257, Bibcode:1971ApJS...23..257W, doi:10.1086/190239. 
  4. ^ a b c d Silvester, J.; et al. (September 2009), "On the incidence of magnetic fields in slowly pulsating B, β Cephei and B-type emission-line stars", Monthly Notices of the Royal Astronomical Society, 398 (3): 1505−1511, arXiv:0906.1575Freely accessible, Bibcode:2009MNRAS.398.1505S, doi:10.1111/j.1365-2966.2009.15208.x. 
  5. ^ Wilson, Ralph Elmer (1953), General Catalogue of Stellar Radial Velocities, Washington: Carnegie Institution of Washington, Bibcode:1953GCRV..C......0W. 
  6. ^ a b Pourbaix, D.; et al. (2004), "SB9: The ninth catalogue of spectroscopic binary orbits", Astronomy & Astrophysics, 424 (2): 727, arXiv:astro-ph/0406573Freely accessible, Bibcode:2004A&A...424..727P, doi:10.1051/0004-6361:20041213. 
  7. ^ a b c d Tetzlaff, N.; et al. (January 2011), "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun", Monthly Notices of the Royal Astronomical Society, 410 (1): 190–200, arXiv:1007.4883Freely accessible, Bibcode:2011MNRAS.410..190T, doi:10.1111/j.1365-2966.2010.17434.x. 
  8. ^ a b Pasinetti Fracassini, L. E.; et al. (February 2001), "Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS)", Astronomy and Astrophysics (3rd ed.), 367: 521–524, arXiv:astro-ph/0012289Freely accessible, Bibcode:2001A&A...367..521P, doi:10.1051/0004-6361:20000451. 
  9. ^ a b Hohle, M. M.; et al. (April 2010), "Masses and luminosities of O- and B-type stars and red supergiants", Astronomische Nachrichten, 331 (4): 349, arXiv:1003.2335Freely accessible, Bibcode:2010AN....331..349H, doi:10.1002/asna.200911355. 
  10. ^ a b c d Prugniel, Ph.; et al. (July 2011), "The atmospheric parameters and spectral interpolator for the MILES stars", Astronomy & Astrophysics, 531: A165, arXiv:1104.4952Freely accessible, Bibcode:2011A&A...531A.165P, doi:10.1051/0004-6361/201116769. 
  11. ^ "pi.02 Cyg -- Spectroscopic binary", SIMBAD Astronomical Database, Centre de Données astronomiques de Strasbourg, retrieved 2017-02-19. 
  12. ^ Eggleton, P. P.; Tokovinin, A. A. (September 2008), "A catalogue of multiplicity among bright stellar systems", Monthly Notices of the Royal Astronomical Society, 389 (2): 869–879, arXiv:0806.2878Freely accessible, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x. 
  13. ^ O'Meara, Stephen James (2016), Deep-Sky Companions: The Caldwell Objects (2nd ed.), Cambridge University Press, p. 92, ISBN 1316033538. 
  14. ^ 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. 
  15. ^ Mason, B. D.; et al. (2014), "The Washington Visual Double Star Catalog", The Astronomical Journal, 122: 3466–3471, Bibcode:2001AJ....122.3466M, doi:10.1086/323920. 
  16. ^ (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 7 日