Pi1 Cygni

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For other stars with this Bayer designation, see π Cygni.
Pi1 Cygni
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Cygnus
Right ascension 21h 42m 05.66458s[1]
Declination +51° 11′ 22.6415″[1]
Apparent magnitude (V) 4.66[2]
Spectral type B3 IV[3]
B−V color index −0.11[2]
Proper motion (μ) RA: +5.29[1] mas/yr
Dec.: −1.78[1] mas/yr
Parallax (π) 1.89 ± 0.15[1] mas
Distance 1,700 ± 100 ly
(530 ± 40 pc)
Period (P) 26.33 d
Eccentricity (e) 0.00
Periastron epoch (T) 2431306.5 ± 10.0 JD
Argument of periastron (ω)
Semi-amplitude (K1)
16.5 km/s
π1 Cyg A
Mass 10.1±0.1[3] M
Radius 5.6[5] R
Luminosity 16,538[6] L
Temperature 18,360±1,100[2] K
Rotational velocity (v sin i) 55[7] km/s
Age 25.1±0.8[3] Myr
Other designations
π1 Cyg, 80 Cygni, BD+50° 3410, FK5 3733, HD 206672, HIP 107136, HR 8301, SAO 33665.[8]

Pi1 Cygni (π1 Cygni, abbreviated Pi1 Cygni, π1 Cygni), also named Azelfafage,[9] is a binary star[4] system in the northern constellation of Cygnus. It is visible to the naked eye, having a combined apparent visual magnitude of 4.66.[2] The distance to this system can be roughly gauged by its annual parallax shift of 1.89 mas,[1] which yields a separation of around 1,700 light years from the Sun, give or take a hundred light years.

This is a single-lined spectroscopic binary with a close, circular orbit, having a period of just 26.33 days. The primary, component A, is a slightly evolved B-type subgiant star with a stellar classification of B3 IV.[3] It has an estimated 10 times the mass of the Sun and around 5.6[5] times the Sun's radius. The star radiates 16,538[6] times the solar luminosity from its outer atmosphere at an effective temperature of roughly 18,360 K.[2] It is about 25[3] million years old and is spinning with a projected rotational velocity of 55 km/s.[7]


π1 Cygni (Latinised to Pi1 Cygni) is the star's Bayer designation. It is also designated HIP 107136 and HR 8301

It bore the traditional name Azelfafage, derived from the Arabic ظلف الفرس Dhilf al-faras meaning "the horse track" or (probably) ذيل الدجاجة Dhail al-dajājah meaning "the tail of hen".[10] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[11] to catalogue and standardize proper names for stars. The WGSN approved the name Azelfafage for this star on 12 September 2016 and it is now so entered in the IAU Catalog of Star Names.[9]

In Chinese, 螣蛇 (Téng Shé), meaning Flying Serpent, refers to an asterism consisting of Pi¹ Cygni, Alpha Lacertae, 4 Lacertae, Pi² Cygni, HD 206267, Epsilon Cephei, Beta Lacertae, Sigma Cassiopeiae, Rho Cassiopeiae, Tau Cassiopeiae, AR Cassiopeiae, 9 Lacertae, 3 Andromedae, 7 Andromedae, 8 Andromedae, Lambda Andromedae, Kappa Andromedae, Psi Andromedae and Iota Andromedae. Consequently, Pi¹ Cygni itself is known as 螣蛇四 (Téng Shé sì, English: the Fourth Star of Flying Serpent)[12]


  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 e Soubiran, C.; et al. (June 2010), "The PASTEL catalogue of stellar parameters", Astronomy and Astrophysics, 515: A111, arXiv:1004.1069Freely accessible, Bibcode:2010A&A...515A.111S, doi:10.1051/0004-6361/201014247. 
  3. ^ a b c d e 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. 
  4. ^ 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. 
  5. ^ 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. 
  6. ^ 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. 
  7. ^ a b Strom, Stephen E.; et al. (2005), "B Star Rotational Velocities in h and χ Persei: A Probe of Initial Conditions during the Star Formation Epoch?", The Astronomical Journal, 129 (2): 809–828, arXiv:astro-ph/0410337Freely accessible, Bibcode:2005AJ....129..809S, doi:10.1086/426748. 
  8. ^ "pi.01 Cyg -- Spectroscopic binary", SIMBAD Astronomical Database, Centre de Données astronomiques de Strasbourg, retrieved 2017-02-19. 
  9. ^ a b IAU Division C Working Group on Star Names (February 1, 2017), IAU Catalog of Star Names, retrieved 2017-02-19. 
  10. ^ p. 197, Star-names and Their Meanings, Richard Hinckley Allen, New York, G. E. Stechert, 1899.
  11. ^ IAU Working Group on Star Names (WGSN), International Astronomical Union, retrieved 22 May 2016. 
  12. ^ (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 7 日