W UMa Binaries

Abstract

The origin and evolution of contact (W UMa) binaries are discussed with the help of the braking law of eq.(1). Best observationally justified parameter-values in (1) for W UMa, CV and LMXB binaries are: α ≈ 1.5, γ = 2 and f computed from eq.(2). A semi-empirical relation (eq.(5)) between the scaled magnetic torque and the fractional X-ray luminosity is proposed. First attempts of simultaneous photometric and spectroscopic surface imaging of contact binaries are described.