Albireo

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Albireo Template:IPAc-en<ref name=Kunitzsch/> is a binary star designated Beta Cygni (β Cygni, abbreviated Beta Cyg, β Cyg). The International Astronomical Union uses the name "Albireo" specifically for the brightest star in the system.<ref name="IAU-CSN"/> Although 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, itself a very close trinary system, makes a striking colour contrast with its fainter blue companion.<ref name=stars/>

NomenclatureEdit

File:CygnusCC.jpg

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 wellTemplate:SndIdeler 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.<ref>p. 24, The names of the stars and constellations compiled from the Latin, Greek and Arabic, W. H. Higgins, Leicester: Samuel Clarke, 1882.</ref> 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.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }} Allen quotes (in translation) a passage from Ideler's Untersuchungen über den Ursprung und die Bedeutung der Sternnamen (1809), page 75.</ref> 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 (IAU) organized a Working Group on Star Names (WGSN)<ref name="WGSN"/> to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016<ref name="WGSN1"/> 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.<ref name="IAU-CSN"/>

Medieval Arabic-speaking astronomers called Beta Cygni Template:Transliteration (English: the hen's beak).<ref>p. 196, Star-names and Their Meanings, Richard Hinckley Allen, New York, G. E. Stechert, 1899.</ref> The term Template:Transliteration (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.<ref name=knobel1895/>

Since Cygnus is the swan, and Beta Cygni is located at the head of the swan, it is sometimes called the "beak star".<ref>p. 416, In Quest of the Universe, Theo Koupelis and Karl F. Kuhn, 5th ed., Sudbury, Massachusetts: Jones & Bartlett Publishers, 2007, Template:ISBN.</ref> With Deneb, Gamma Cygni (Sadr), Delta Cygni, and Epsilon Cygni (Gienah), it forms the asterism called the Northern Cross.<ref name=darling/>

PropertiesEdit

File:NewAlbireo.jpg

Albireo A and B

Beta Cygni is about Template:Convert away from the Sun.<ref name=drimmel2021/> 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).<ref name=msg /> Separated by 35 seconds of arc,<ref name=wdsb>Entry, The Washington Double Star Catalog, identifier 19307+2758, discoverer identifier STFA 43. Accessed on line July 9, 2008.</ref> 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.<ref name=drimmel2021/> If they are a physical binary, their orbital period is probably at least 100,000 years.<ref name=msg>p. 46, The Monthly Sky Guide, Ian Ridpath, Wil Tirion, Cambridge University Press, 2006, Template:ISBN.</ref> 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.<ref name="SkyTel1"/> The primary and secondary also have different measured distances from the Hipparcos mission – Template:Convert for the primary and Template:Convert for the secondary.<ref name=hipparcos/> 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.<ref name=dr2distances/>

In around 3.87 million years, Albireo will become the brightest star in the night sky.<ref name=tomkin1998>Template:Cite journal – based on computations from HIPPARCOS data. (The calculations exclude stars whose distance or proper motion is uncertain.) PDF Template:Dead link Template:Cbignore</ref> It will peak in brightness with an apparent magnitude of –0.53 in 4.61 million years.<ref name=tomkin1998 />

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.<ref name=wdsa>Entry, WDS identifier 19307+2758, Sixth Catalog of Orbits of Visual Binary Stars Template:Webarchive, William I. Hartkopf & Brian D. Mason, U.S. Naval Observatory. Accessed on line July 9, 2008. (19307+2758) Template:Webarchive</ref>

Albireo AEdit

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.<ref name=maury1897/> This was supported by observations from 1898 to 1918 which showed that it had a varying radial velocity.<ref name=campbell1919/> In 1923, the two components were identified in the Henry Draper Catalogue as HD 183912 and HD 183913.<ref name=freestarcharts/><ref name=hd/>

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,<ref name=bonneau/> and the companion is referred to as component Ab in the Washington Double Star Catalog.<ref name=wdsa/>

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.<ref name=pisco/><ref name=mcalister1982/> 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.<ref name=wdsa/> It is designated as component C in the Catalog of Components of Double and Multiple Stars,<ref name=ccdm/> not to be confused with component C in the Washington Double Star Catalog which is a faint optical companion.<ref name=wdsa/> 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.<ref name=pisco/> The confirmed close pair are referred to as Aa and Ac in modern papers, with Ab being the unconfirmed third component.<ref name=drimmel2021/> A 2022 study treats the existence of Albireo Ab as "very unlikely".<ref name="Albireo Ad"/>

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.<ref name="Albireo Ad">Template:Cite journal</ref>

The diameter of the primary K-type giant star has been measured using interferometry from the Navy Precision Optical Interferometer. A limb-darkened angular diameter of Template:Val was measured. At the parallax-derived distance of 111.4Template:Nbsppc, a radius equivalent to Template:Solar radius is calculated.<ref name="npoi">Template:Citation</ref>

Albireo BEdit

β Cygni B is a fast-rotating Be star, with an equatorial rotational velocity of at least 250 kilometers per second.<ref name="stars"/> Its surface temperature has been spectroscopically estimated to be about 13,200 K.<ref name=physparms/>

β Cygni B has been reported to be a very close double,<ref name=roberts/> but the observations appear to have been incorrect.<ref name=wdsa/>

Moving groupEdit

Analysis of Gaia Data Release 2 astrometry suggests that four fainter stars may form a moving group along with the brighter visible components.<ref name=drimmel2021/>