Editing Albireo (section)

===Albireo A===
The [[stellar spectrum|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">{{Cite journal |last1=Jack |first1=D. |last2=Schröder |first2=K.-P. |last3=Mittag |first3=M. |last4=Bastian |first4=U. |date=2022-05-01 |title=Yet another star in the Albireo system - The discovery of Albireo Ad |url=https://www.aanda.org/articles/aa/full_html/2022/05/aa43255-22/aa43255-22.html |journal=Astronomy & Astrophysics |language=en |volume=661 |pages=A49 |doi=10.1051/0004-6361/202243255 |issn=0004-6361|arxiv=2203.04222 |bibcode=2022A&A...661A..49J }}</ref>

The diameter of the primary K-type giant star has been measured using [[interferometry]] from the [[Navy Precision Optical Interferometer]]. A [[Limb darkening|limb-darkened]] angular diameter of {{val|4.904|ul=mas}} was measured. At the [[parallax]]-derived distance of 111.4{{nbsp}}pc, a radius equivalent to {{solar radius|58.69|link=y}} is calculated.<ref name="npoi">{{Citation|last1=Baines |first1=Ellyn K. |last2=Clark |first2=James H., III |last3=Schmitt |first3=Henrique R. |last4=Stone |first4=Jordan M. |last5=von Braun |first5=Kaspar |date=2023-12-01 |title=33 New Stellar Angular Diameters from the NPOI, and Nearly 180 NPOI Diameters as an Ensemble |journal=The Astronomical Journal |volume=166 |issue=6 |pages=268 |doi=10.3847/1538-3881/ad08be |doi-access=free |bibcode=2023AJ....166..268B |issn=0004-6256}}</ref>