Beta Lyrae

β Lyrae (Latinised to Beta Lyrae) is the system's Bayer designation, established by Johann Bayer in his Uranometria of 1603, and denotes that it is the second brightest star in the Lyra constellation. WDS J18501+3322 is a designation in the Washington Double Star Catalog. The designations of the constituents as Beta Lyrae A, B and C, or alternatively WDS J18501+3322A, B and C, and additionally WDS J18501+3322D, E and F, and those of ''A's components - Aa1, Aa2 and Ab'' - derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU). Beta Lyrae bore the traditional name Sheliak (occasionally Shelyak or Shiliak), derived from the Arabic الشلياق šiliyāq or Al Shilyāk, one of the names of the constellation of Lyra in Islamic astronomy. Notably, in Arabic sources the Lyra constellation is primarily referred to as سِلْيَاق (Romanization: Siliyāq), whereas شلياق (Šiliyāq) primarily is used to refer to Beta Lyrae in what might be a form of linguistic reborrowing. Persian sources on the other hand, do refer to the Lyra constellation as شلياق (Šiliyāq), which may be the source of this confusion. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalogue and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems. It approved the name Sheliak for the component Beta Lyrae Aa1 on 21 August 2016 and it is now so included in the List of IAU-approved Star Names. In Chinese astronomy, Tsan Tae ( (), meaning Clepsydra Terrace, refers to an asterism consisting of this star, Delta² Lyrae, Gamma Lyrae and Iota Lyrae. Consequently, the Chinese name for Beta Lyrae itself is (, .) ==Properties==

Beta Lyrae Aa is a semidetached binary system made up of a stellar class B6-8 primary star and a secondary that is probably also a B-type star. The fainter, less massive star in the system was once the more massive member of the pair, which caused it to evolve away from the main sequence first and become a giant star. Because the pair are in a close orbit, as this star expanded into a giant it filled its Roche lobe and transferred most of its mass over to its companion. The secondary, now more massive star is surrounded by an accretion disk from this mass transfer, with bipolar, jet-like features projecting perpendicular to the disk. ==Variability==

for Beta Lyrae, plotted from TESS data The date of a primary minimum can be calculated according the following formula: Primary_Minimum = 2436793.48 + 12.93095*n + 0.00000386*n*n whereby n is a natural number. The calculated date is given in Julian days. ==Companions==

In addition to Beta Lyrae A, several other companions have been catalogued. β Lyr B, at an angular separation of 45.7", is of spectral type B7V, has an apparent magnitude of +7.2, and can easily be seen with binoculars. It is about 80 times as luminous as the Sun. In 1962 it was identified as spectroscopic binary with a period of 4.348 days, but the 2004 release of the SB9 catalog of Spectroscopic Binary Orbits omitted it, so it is now considered a single star. both are catalogued as Ap stars, although component F is sometimes thought to be an Am star. Component C has been observed to vary in brightness by over a magnitude, but the type of variability is not known. Components A, B, and F are thought to be members of a group of stars around β Lyrae, at approximately the same distance and moving together. The others just happen to be in the same line of sight. Analysis of Gaia Data Release 2 astrometry reveals a group of about 100 stars around β Lyrae which share its space motion and are at the same distance. This cluster has been named Gaia 8. The cluster members are all main sequence stars and the lack of a main sequence turnoff means that a precise age cannot be calculated, but the cluster age is estimated at 30 to 100 million years. The average Gaia DR2 parallax for the member stars is . The Gaia spacecraft has provided these data for the stars listed in the WDS: == References ==