Pi1 Cygni

Pi¹ Cygni (π¹ Cygni, abbreviated Pi¹ Cyg, π¹ Cyg) is a binary star[5] 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.

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]
Characteristics
Spectral type B3 IV[3]
B−V color index −0.11[2]
Astrometry
Proper motion (μ) RA: +5.29[1] mas/yr
Dec.: −1.78[1] mas/yr
Parallax (π)1.89 ± 0.15[1] mas
Distance1,700 ± 100 ly
(530 ± 40 pc)
Absolute magnitude (MV)−3.91[4]
Orbit[5]
Period (P)26.33 d
Eccentricity (e)0.00
Periastron epoch (T)2431306.5 ± 10.0 JD
Argument of periastron (ω)
(secondary)		0.00°
Semi-amplitude (K1)
(primary)		16.5 km/s
Details
π¹ Cyg A
Mass10.1±0.1[3] M☉
Radius5.6[6] R☉
Luminosity16,538[7] L☉
Temperature18,360±1,100[2] K
Rotational velocity (v sin i)55[8] km/s
Age25.1±0.8[3] Myr
Other designations
π¹ Cyg, 80 Cygni, BD+50° 3410, FK5 3733, HD 206672, HIP 107136, HR 8301, SAO 33665.[9]
Database references
SIMBADdata

The two components are designated Pi¹ Cygni A (officially named Azelfafage /əˈzɛlfəfeɪdʒ/, the traditional name for the system)[10] and B.

Nomenclature

π¹ Cygni (Latinised to Pi¹ Cygni) is the star's Bayer designation. The designations of the two components as Pi¹ Cygni A and B derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).[11]

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".[12] In 2016, the IAU organized a Working Group on Star Names (WGSN)[13] to catalogue and standardize proper names for stars. The WGSN approved the name Azelfafage for Pi¹ Cygni on 12 September 2016 and it is now so included in the List of IAU-approved Star Names.[10] For such names relating to members of multiple star systems, and where a component letter is not explicitly listed, the WGSN says that the name should be understood to be attributed to the brightest component by visual brightness[14] - in this case Pi¹ Cygni A.

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, the Chinese name for Pi¹ Cygni itself is 螣蛇四 (Téng Shé sì, English: the Fourth Star of Flying Serpent)[15]

Properties

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[6] times the Sun's radius. The star radiates 16,538[7] 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.[8]

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, S2CID 18759600.
  2. Soubiran, C.; et al. (June 2010), "The PASTEL catalogue of stellar parameters", Astronomy and Astrophysics, 515: A111, arXiv:1004.1069, Bibcode:2010A&A...515A.111S, doi:10.1051/0004-6361/201014247, S2CID 118362423.
  3. 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:1007.4883, Bibcode:2011MNRAS.410..190T, doi:10.1111/j.1365-2966.2010.17434.x, S2CID 118629873.
  4. 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.
  5. Pourbaix, D.; et al. (2004), "SB9: The ninth catalogue of spectroscopic binary orbits", Astronomy & Astrophysics, 424 (2): 727–732, arXiv:astro-ph/0406573, Bibcode:2004A&A...424..727P, doi:10.1051/0004-6361:20041213, S2CID 119387088.
  6. Pasinetti Fracassini, L. E.; et al. (February 2001), "Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS)", Astronomy and Astrophysics (3rd ed.), 367 (2): 521–524, arXiv:astro-ph/0012289, Bibcode:2001A&A...367..521P, doi:10.1051/0004-6361:20000451, S2CID 425754.
  7. 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:1003.2335, Bibcode:2010AN....331..349H, doi:10.1002/asna.200911355, S2CID 111387483.
  8. 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/0410337, Bibcode:2005AJ....129..809S, doi:10.1086/426748, S2CID 15059129.
  9. "pi.01 Cyg -- Spectroscopic binary", SIMBAD Astronomical Database, Centre de Données astronomiques de Strasbourg, retrieved 2017-02-19.
  10. "Naming Stars". IAU.org. Retrieved 16 December 2017.
  11. Hessman, F. V.; Dhillon, V. S.; Winget, D. E.; Schreiber, M. R.; Horne, K.; Marsh, T. R.; Guenther, E.; Schwope, A.; Heber, U. (2010). "On the naming convention used for multiple star systems and extrasolar planets". arXiv:1012.0707 [astro-ph.SR].
  12. p. 197, Star-names and Their Meanings, Richard Hinckley Allen, New York, G. E. Stechert, 1899.
  13. IAU Working Group on Star Names (WGSN), International Astronomical Union, retrieved 22 May 2016.
  14. "Bulletin of the IAU Working Group on Star Names, No. 2" (PDF). Retrieved 16 December 2017.
  15. (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 7 日
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