Epoch J2000.0 Equinox J2000.0 (ICRS)
|Right ascension||19h 30m 43.286s|
|Declination||+27° 57′ 34.84″|
|Apparent magnitude (V)||3.18|
|Right ascension||19h 30m 43.295s|
|Declination||+27° 57′ 34.62″|
|Apparent magnitude (V)||5.82|
|Right ascension||19h 30m 45.3954s|
|Declination||+27° 57′ 54.995″|
|Apparent magnitude (V)||5.09|
|B−V color index||1.074|
|V−R color index||0.92|
|B−V color index||0.09|
|V−R color index||0.09|
|U−B color index||-0.30|
|B−V color index||-0.06|
|Radial velocity (Rv)||-24.07 km/s|
|Proper motion (μ)||RA: -7.17 mas/yr
Dec.: -6.15 mas/yr
|Parallax (π)||7.51 ± 0.33[a] mas|
|Distance||430 ± 20 ly
(133 ± 6 pc)
|Absolute magnitude (MV)||−2.45|
|Absolute magnitude (MV)||−0.25|
|Radial velocity (Rv)||-18 km/s|
|Proper motion (μ)||RA: -1.95 mas/yr
Dec.: -0.98 mas/yr
|Parallax (π)||8.16 ± 0.25[a] mas|
|Distance||400 ± 10 ly
(123 ± 4 pc)
|Period (P)||213.859 yr|
|Semi-major axis (a)||0.536″|
|Longitude of the node (Ω)||170.4°|
|Periastron epoch (T)||B1997.995|
|Argument of periastron (ω)
|Luminosity (bolometric)||1,200 ± 200 L☉|
|Surface gravity (log g)||2.0 cgs|
|Metallicity [Fe/H]||−0.1 dex|
|Rotational velocity (v sin i)||1.4 km/s|
|Luminosity (bolometric)||950 ± 250 L☉|
|Mass||3.7 ± 0.8 M☉|
|Luminosity (bolometric)||230 ± 90 L☉|
|Surface gravity (log g)||4.00 ± 0.15 cgs|
|Temperature||13,200 ± 600 K|
|Position (relative to Albireo A)|
|Epoch of observation||2006|
|Angular distance||35.3″ |
|Position angle||54° |
|AlbireoA: β¹ Cygni, BD+27 3410, HR 7417, HD 183912/183913, HIP 95947, SAO 87301, FK5 732, MCA 55 Aac, NSV 12105|
|AlbireoB: β² Cygni, STF 4043B, BD+27 3411, HD 183914, HIP 95951, HR 7418, SAO 87302|
Albireo is the traditional name for the double star also designated Beta Cygni (β Cygni, abbreviated Beta Cyg, β Cyg), although the International Astronomical Union now regards the name as only applying to the brightest component. Despite being designated 'beta', it is fainter than Gamma Cygni, Delta Cygni, and Epsilon Cygni and is the fifth-brightest point of light in the constellation of Cygnus. Appearing to the naked eye to be a single star of magnitude 3, viewing through even a low-magnification telescope resolves it into its two components. The brighter yellow star (actually itself a very close binary system) makes a striking colour contrast with its fainter blue companion.
The system's traditional name Albireo is a result of misunderstanding and mistranslation. It is thought that it originated in the Greek name ornis for the constellation of Cygnus, which became urnis in Arabic. When translated into Latin, this name was thought to refer to the Greek name Erysimon for the plant Sisymbrium officinale (which in Latin is ireo), and so was described in Latin in the Arabo-Latin Almagest of 1515 as "Eurisim: et est volans; et jam vocatur gallina. et dicitur eurisim quasi redolens ut lilium ab ireo" ("Eurisim: and it is the flyer, and now it is called the hen, and it is called Eurisim, as if redolent like the lily from the 'ireo'"), via a confusion between ireo and the scented flower Iris florentina. This was variously miscopied, until "ab ireo" was treated as a miscopy of an Arabic term and changed into al-bireo. 
In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016 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.
Medieval Arabic-speaking astronomers called Beta Cygni minqār al-dajājah (English: the hen's beak). 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.
Since Cygnus is the swan, and Beta Cygni is located at the head of the swan, it is sometimes called the "beak star". With Deneb, Gamma Cygni (Sadr), Delta Cygni, and Epsilon Cygni (Gienah), it forms the asterism called the Northern Cross.
When viewed with the naked eye, Albireo appears to be a single star. However, in a telescope it readily 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). Separated by 35 seconds of arc, 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. If they are a physical binary, their orbital period is probably at least 100,000 years. Some experts, however, support the optical double argument, based on observations that suggest different proper motions for the components, which implies they're unrelated.
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.
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. This was supported by observations from 1898 to 1918 which showed that it had a varying radial velocity. In 1923, the two components were identified in the Henry Draper Catalogue as HD 183912 and HD 183913.
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, and the companion is referred to as component Ab in the Washington Double Star Catalog.
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 specifically noted that the observation was inconsistent with the Haute-Provence observations and hence not of the same star. 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. It is designated as component C in the Catalog of Components of Double and Multiple Stars, not to be confused with component C in the Washington Double Star Catalog which is a faint optical companion. 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.
The status of the two possible companions is still not clarified. One set of observations reports barely resolving two components, but there has not been confirmation of this. Observations of Albireo assuming the spectrum is a composite of two stars derive a late B spectral type for the companion,, for example B8. Adaptive optics measurements of the companion are best modelled by a B0V spectrum for the companion with an apparent magnitude of 5.85. Different assumptions about the spectral type of the companion lead to wildly different physical properties, for example an effective temperature of either 12,000 K or 30,000 K.
The diameter of the primary K-type giant star has been measured using interferometry. A uniform disk of approximately 4.5 mas was measured at optical and near-infrared wavelengths, and a limb-darkened diameter of 4.834 mas was calculated, equivalent to a radius of 69 R☉ at a distance of 133 pc.
β Cygni B is a fast-rotating Be star, with an equatorial rotational velocity of at least 250 kilometers per second. Its surface temperature has been spectroscopically estimated to be about 13,200 K.
- The primary and secondary have different formal Hipparchos parallaxes. They are thought to be physically related and so at the same distance from Earth in astronomical terms, hence one or both derived distances are somewhat in error.
- , Hipparcos catalogue; CDS.
- Binary Star Differential Photometry Using the Adaptive Optics System at Mount Wilson Observatory, Theo ten Brummelaar, Brian D. Mason, et al., Astronomical Journal 119, #5 (May 2000), pp. 2403–2414. doi:10.1086/301338. Bibcode: 2000AJ....119.2403T. See tables 4, 5, 6, and 8. Luminosity from Lbol=102(4.75−Mbol)/5.
- , Hipparcos catalogue; CDS.
- HD 183914 -- Emission-line Star, database entry, SIMBAD. Accessed on line July 9, 2008.
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- Knobel, E. B. (June 1895). "Al Achsasi Al Mouakket, on a catalogue of stars in the Calendarium of Mohammad Al Achsasi Al Mouakket". Monthly Notices of the Royal Astronomical Society. 55 (8): 429. Bibcode:1895MNRAS..55..429K. doi:10.1093/mnras/55.8.429.
- p. 416, In Quest of the Universe, Theo Koupelis and Karl F. Kuhn, 5th ed., Sudbury, Massachusetts: Jones & Bartlett Publishers, 2007, ISBN 0-7637-4387-9.
- Northern Cross, entry, The Internet Encyclopedia of Science, David Darling. Accessed on line July 24, 2008.
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- "freestarcharts.com". Retrieved 2017-06-11.
- Cannon, Annie Jump; Pickering, Edward Charles (1923). "The Henry Draper catalogue : 19h and 20h". Annals of the Astronomical Observatory of Harvard College ; v. 98. 98. Bibcode:1923AnHar..98....1C.. See note re HD 183912,3,4 on this page.
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- 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.
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- Prieur, J.-L.; Koechlin, L.; Ginestet, N.; Carquillat, J.-M.; Aristidi, E.; Scardia, M.; Arnold, L.; Avila, R.; Festou, M. C.; Morel, S.; Pérez, J.-P. (2002). "Speckle Observations of Composite Spectrum Stars with PISCO in 1993-1998". The Astrophysical Journal Supplement Series. 142: 95. Bibcode:2002ApJS..142...95P. doi:10.1086/341094.
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- NASA Astronomy Picture of the Day: Albireo: A Bright and Beautiful Double (30 August 2005)
- A picture of Albireo by Stefan Seip
- Albireo at Pete Roberts' Fuzzy Blobs site
- About Cygnus, including more information about the origin of the name Albireo.
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