Zeta^1,2 Lyrae

A multiple system in the constellation of Lyra that lies southeastward of the brilliant star Vega in the sky. The system lies approximately 158 light years from the Sun, and contains at least three stars, and possibly several more. The two main stars of the system form an extremely wide pair, estimated to lie some 2,000 AU apart (that is, about seventy times as far from one another as Neptune is from the Sun). At this great distance, their mutual orbit takes millennia to complete, and it is estimated that their orbital cycle may take as many as 50,000 years to complete.

Their wide separation in space means that the two component stars are clearly distinguishable from one another, and indeed these components are given their own individual designations. The brighter of the pair is designated Zeta¹ Lyrae (or sometimes Zeta Lyrae A) or 6 Lyrae on the Flamsteed system, while Zeta² Lyrae is also known as Zeta Lyrae B or 7 Lyrae. Zeta¹ shines at fourth magnitude, while Zeta² is somewhat fainter, with a visual magnitude of +5.59 (that is, barely visible to the naked eye).

Zeta¹ Lyrae is not in fact a single star, but a spectroscopic binary. Its companion follows an extremely close orbit around the star, hurtling around Zeta¹ in just over four days. The spectrum of Zeta¹ Lyrae reveals a star with peculiar chemical properties, showing unusual concentrations of metals (in this context, heavier elements like iron) in its outer layers.

Zeta² Lyrae shows no such peculiarites, though it is notable for its extremely rapid rate of rotation, fast enough to deform the star into a flattened oblate shape. There are indications that, like Zeta¹, Zeta² may also have a low-mass companion star in orbit. Thus the entire system may contain four stars, with a pair of close binaries in a much more distant orbit around one another. It is thought that there may potentially be even more members of the system, in yet more distant orbits around the main pair of stars.