OAO-2 observations of the helium spectrum variable a Centauri.

Ultraviolet photometry and spectrometer data are presented for a Cen, which exhibits large variations in the strength of its He I lines. The photometry indicates that the star becomes brighter at the helium-weak phase by 0.03 mag throughout the ultraviolet and visual region. A model atmosphere analysis indicates that the photometric variations are not due to flux redistribution from back-warming effects, but can be interpreted as due to the rotation of a distorted steilar disk in the shape of a prolate spheroid. Subject headings: spectrum variables - stars, individual - ultraviolet