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We present a spectroscopic characterisation and a new orbital solution forthe binary system beta Cyg Aa/Ac (MCA 55), the primary component (beta Cyg A)of the well-known wide double star Albireo. By matching evolutionary tracks tothe physical parameters of all three Albireo stars (beta Cyg Aa, Ac and B) asobtained from a spectroscopic analysis of TIGRE and IUE spectra, we confirmthat they are likely coeval. Our final orbit solution is based onradial-velocity measurements taken over a baseline exceeding $120$ years,combined with relative astrometry from speckle interferometric observations andthe absolute astrometry from the Hipparcos and Gaia missions. Our final orbitsolution has a period of $121.65^{+3.34}_{-2.90}$ years with an eccentricity of$0.20^{+0.01}_{-0.02}$. Thanks to the inclusion of the absolute astrometry, wefind a mass ratio of $q = 1.25^{+0.19}_{-0.17}$, and a total mass of$9.47_{-3.24}^{+5.88}$ M$_\odot$, indicating that the secondary (Ac) is themore massive of the pair. These results strongly suggest the presence of afourth, unseen, member of the Albireo system. Given the current photometricdata it is likely that beta Cyg A is itself a hierarchical triple. We alsoderive the systemic proper motion, line-of-sight velocity, and an orbitalparallax of the beta Cyg A system, allowing us to quantitatively assess thehypothesis that Albireo A and B form a physically bound and genealogicallyconnected system. Finally, we find four potential members of a common propermotion group with Albireo, though none anywhere as close by as the Albireocomponents A to B.

A celestial matryoshka: Dynamical and spectroscopic analysis of the Albireo system