University of Wisconsin

Space Astronomy Laboratory

ASTRO - 2

WUPPE

OBJECT: Beta Lyra (BET-LYR)
Other names: HD 174638, Sheliak
ID # 3323

UW Astronomer: Geoff Fox


Beta Lyrae is a binary system located about 860 light years away in the constellation of Lyra. The primary star is a young B star, with a diameter 19 times that of our Sun, and it shines 3000 times brighter.

Beta Lyra is the prototype of a class of eclipsing binary stars, the Beta Lyrids. It goes through an eclipse with its companion every 13 days, varying in magnitude from 3.4 to 4.3.

The secondary star, a late A star, has a diameter 15 times that of our Sun. Due to a separation of only 22 million miles, their atmospheres mix (mass from the primary flows to the secondary), causing the orbital period to increase by 9.2 seconds annually. Once the mass of the primary star equals the mass of the secondary star, the process will reverse. Rapid rotation and gravitational distortion make both of these stars ellipsoidal in shape.

Analysis of WUPPE and HPOL observations suggests that the UV bump, Balmer emission, and near-UV continuum polarization is produced by electron scattering in a flow out of the two poles of the system. The variable polarization in the visible undergoes eclipses, and so is associated with material near the accretion disk.

The results have appeared.