Albireo is the star in the head of the constellation of Cygnus (bottom).
β Cygni (Latinised to Beta Cygni) is the system's Bayer designation. The brighter of the two components is designated β¹ Cygni or Beta Cygni A and the fainter β² Cygni or Beta Cygni B.
The origin of the star system's traditional name Albireo is unclear. Christian Ludwig Ideler traced it to the heading for the constellation we call Cygnus in Ptolemy's star catalog, in the translation of the Almagest by Gerard of Cremona: "Stellatio Eurisim: et est volans; et jam vocatur gallina. et dicitur eurisim quasi redolens ut lilium ab ireo" ("Constellation Eurisim: and it is the Flyer, and it is also called the Hen, and it is called Eurisim as if redolent like the lily from the 'ireo'"). (The original Greek just calls the constellation "Ορνιθος αστερισμος", "the constellation of the Bird".) The word "ireo" is obscure as well – Ideler suggests that Gerard took "Eurisim" to mean the plant Erysimum, which is called irio in Latin, but the ablative case of that is not "ireo" but irione.[26] In any case, Ideler proposed that (somehow) the phrase "ab ireo" was applied to the star at the head of the bird, and this became "Albireo" when an "l" was mistakenly inserted as though it was an Arabic name.[27] Ideler also supposed that the name Eurisim was a mistaken transliteration of the Arabic name "Urnis" for Cygnus (from the Greek "Ορνις").
In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[28] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[29] included a table of the first two batches of names approved by the WGSN; which included Albireo for β¹ Cygni. It is now so entered in the IAU Catalog of Star Names.[24]
Medieval Arabic-speaking astronomers called Beta Cygni minqār al-dajājah (English: the hen's beak).[30] The term minqār al-dajājah (منقار الدجاجة) or Menchir al Dedjadjet appeared in the catalogue of stars in the Calendarium of Al Achsasi Al Mouakket, which was translated into Latin as Rostrum Gallinae, meaning the hen's beak.[31]
Beta Cygni is about 420 light-years (129 pc) away from the Sun.[2] When viewed with the naked eye, Albireo appears to be a single star. However, in a telescope it resolves into a double star consisting of β Cygni A (amber, apparent magnitude 3.1), and β Cygni B (blue-green, apparent magnitude 5.1).[34] Separated by 35 seconds of arc,[13] the two components provide one of the best contrasting double stars in the sky due to their different colors.
It is not known whether the two components β Cygni A and B are orbiting around each other in a physical binary system, or if they are merely an optical double.[2] If they are a physical binary, their orbital period is probably at least 100,000 years.[34] Some experts, however, support the optical double argument, based on observations that suggest different proper motions for the components, which implies that they are unrelated.[35] The primary and secondary also have different measured distances from the Hipparcos mission – 434 ± 20 light-years (133 ± 6 pc) for the primary and 401 ± 13 light-years (123 ± 4 pc) for the secondary.[36] More recently the Gaia mission has measured distances of about 330–390 light years (100–120 parsecs) for both components, but noise in the astrometric measurements for the stars means that data from Gaia's second data release is not yet sufficient to determine whether the stars are physically associated.[37]
In around 3.87 million years, Albireo will become the brightest star in the night sky.[38] It will peak in brightness with an apparent magnitude of –0.53 in 4.61 million years.[38]
There are a further 10 faint companions listed in the Washington Double Star catalogue, all fainter than magnitude 10. Only one is closer to the primary than Albireo B, with the others up to 142" away.[20]
Albireo A
The spectrum of Beta Cygni A was found to be composite when it was observed as part of the Henry Draper Memorial project in the late 19th century, leading to the supposition that it was itself double.[39] This was supported by observations from 1898 to 1918 which showed that it had a varying radial velocity.[40] In 1923, the two components were identified in the Henry Draper Catalogue as HD 183912 and HD 183913.[41][42]
In 1978, speckle interferometry observations using the 1.93m telescope at the Haute-Provence Observatory resolved a companion at 0.125". This observation was published in 1980,[43] and the companion is referred to as component Ab in the Washington Double Star Catalog.[20]
In 1976 speckle interferometry was used to resolve a companion using the 2.1-meter telescope at the Kitt Peak National Observatory. It was measured at a separation of 0.44", and it is noted that the observation was inconsistent with the Haute-Provence observations and hence not of the same star.[21][44] Although these observations pre-dated those at Haute-Provence, they were not published until 1982 and this component is designated Ac in the Washington Double Star Catalog.[20] It is designated as component C in the Catalog of Components of Double and Multiple Stars,[45] not to be confused with component C in the Washington Double Star Catalog which is a faint optical companion.[20] An orbit for the pair has since been computed using interferometric measurements, but as only approximately a quarter of the orbit has been observed, the orbital parameters must be regarded as preliminary. The period of this orbit is 214 years.[21] The confirmed close pair are referred to as Aa and Ac in modern papers, with Ab being the unconfirmed third component.[2] A 2022 study treats the existence of Albireo Ab as "very unlikely".[16]
In 2022, a third component was found to be orbiting Albireo Aa, named Albireo Ad. It is a very-low-mass star with around 8.5% the Sun's mass and an orbital period of 371 days.[16]
β Cygni B is a fast-rotating Be star, with an equatorial rotational velocity of at least 250 kilometers per second.[25] Its surface temperature has been spectroscopically estimated to be about 13,200 K.[17]
β Cygni B has been reported to be a very close double,[46] but the observations appear to have been incorrect.[20]
Moving group
Analysis of Gaia Data Release 2 astrometry suggests that four fainter stars may form a moving group along with the brighter visible components.[2]
^ abcdDucati, J. R (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues. 2237. Bibcode:2002yCat.2237....0D.
^Kharchenko, N. V; Scholz, R.-D; Piskunov, A. E; Röser, S; Schilbach, E (2007). "Astrophysical supplements to the ASCC-2.5: Ia. Radial velocities of ˜55000 stars and mean radial velocities of 516 Galactic open clusters and associations". Astronomische Nachrichten. 328 (9): 889. arXiv:0705.0878. Bibcode:2007AN....328..889K. doi:10.1002/asna.200710776. S2CID119323941.
^ abBaines, Ellyn K.; Clark, James H., III; Schmitt, Henrique R.; Stone, Jordan M.; von Braun, Kaspar (2023-12-01), "33 New Stellar Angular Diameters from the NPOI, and Nearly 180 NPOI Diameters as an Ensemble", The Astronomical Journal, 166 (6): 268, Bibcode:2023AJ....166..268B, doi:10.3847/1538-3881/ad08be, ISSN0004-6256{{citation}}: CS1 maint: multiple names: authors list (link)
^Fracassini, Massimo; Gilardoni, Giorgio; Pasinetti, Laura E. (1973). "Apparent diameters of 172 B5V-A5V stars of the Catalogue of Geneva Observatory". Astrophysics and Space Science. 22 (1): 141–152. Bibcode:1973Ap&SS..22..141F. doi:10.1007/BF00642829. S2CID120496963.
^Kunitzsch, Paul; Smart, Tim (2006). A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations (2nd rev. ed.). Cambridge, Massachusetts: Sky Pub. ISBN978-1-931559-44-7.
^p. 416, In Quest of the Universe, Theo Koupelis and Karl F. Kuhn, 5th ed., Sudbury, Massachusetts: Jones & Bartlett Publishers, 2007, ISBN0-7637-4387-9.
^Maury, Antonia C.; Pickering, Edward C. (1897). "Spectra of bright stars photographed with the 11-inch Draper Telescope as part of the Henry Draper Memorial". Annals of Harvard College Observatory. 28: 1. Bibcode:1897AnHar..28....1M.
^Cannon, Annie Jump; Pickering, Edward Charles (1923). "The Henry Draper catalogue : 19h and 20h". Annals of the Astronomical Observatory of Harvard College. 98: 1. Bibcode:1923AnHar..98....1C.. See note re HD 183912,3,4 on this page.
^Bonneau, D.; Foy, R. (1980). "Speckle interferometric observations of binary systems with the Haute-Provence 1.93 M telescope". Astronomy and Astrophysics. 86: 295. Bibcode:1980A&A....86..295B.
^Dommanget, J.; Nys, O. (1994). "Catalogue des composantes d'etoiles doubles et multiples (CCDM) premiere edition - Catalogue of the components of double and multiple stars (CCDM) first edition". Com. De l'Observ. Royal de Belgique. 115: 1. Bibcode:1994CoORB.115....1D.
Webb, T. W.; McAlister, H. A.; Worley, C. E.; Burnham, S. W.; Aitken, R. G. (1980). "Albireo as a Triple Star". Sky and Telescope. 59: 210. Bibcode:1980S&T....59..210W.
