Coronal loops in binary stars.

Einstein and IUE observations of main sequence close binaries are fitted with approximate power-laws of type F ∝ Ω^αf^β where Ω is the angular velocity and f the convective efficiency. The surface of the most active stars can be visualized to be entirely filled with structures similar to those found in strong solar active regions. The peculiar behaviour of physical-contact binaries of W UMa-type is considered.