Beta Lyrae an eclipsing binary star in the the constellation Lyra, the Harp. Beta Lyrae is the prototype for the class of eclipsing binaries whose components are so close together that they deform each other by their mutual gravitation. Beta Lyrae is traditionally named Sheliak, which is Arabic for "tortoise" or "harp."
Variability
Located 880 light-years away, the β Lyr system actually radiates the visible light of 2000 suns. Its apparent magnitude changes from +3.4 to +4.6 over a period of 12.9075 days, caused by the mutual eclipses of the two close stars as they orbit around each other. Sheliak's variations, easily visible to the naked eye by comparing the star to others in the constellation, were discovered in 1784.
Components
The components are so close together that they cannot be resolved with optical telescopes, but can be detected through spectroscopy. Beta Lyrae's components are a blue-white class B7 V and a white class A8 V main sequence star, with surfaces of 13,000 and 8,000 K, respectively. The two stars are close enough that material from the photosphere of each star is pulled toward the other, drawing them into an ellipsoidal shape. The tidal forces that distort both stars can cause streams of matter to flow from one onto the other, and apparently into a disk around the fainter of two. Such mass transfer is profoundly important in the lives of double stars.
Beta Lyrae is both an eclipsing binary and a visual multiple. The third component, with an apparent magnitude of +7.2, lies at an angular distance of 45.7". It can easily be seen with binoculars, and is of spectral type B7 V. It is about 80 times as luminous as the Sun, and is also a spectroscopic binary, with a period of 4.34 days. There is still another component, of magnitude 9.9, separated by 86", that appears to be part of the β Lyr system, with has a luminosity 7 times the Sun's.
[Adapted from STARS by Jim Kaler, Professor Emeritus of Astronomy, University of Illinois]