Angular momentum loss and the formation of W UMa systems

Angular momentum loss may be introduced as part of the explanation of the peculiar overabundance of W UMa-type contact binaries. Among the various possible mechanisms to achieve this are (i) overflow through the outer Lagrangian point in a deep contact phase (ii) magnetic braking, where magnetic lines of force 'stiffen' and thus enhance the efficiency of angular momentum loss associated with a stellar wind. Such subjects have been investigated in a number of more recent detailed studies. (Auth.)