On the structure and evolution of W UMa systems.
Abstract
An attempt is made to construct and follow the initial evolution of models of zeroage contact binary systems having long nuclear evolutionary time scales and showing rapid period changes. Gravitational energy due to mass transfer is taken into account, and the phase where an abrupt change occurs in the direction of mass transfer is investigated. Calculations performed for a grid of thermalequilibrium models indicate that zeroage evolution proceeds on a time scale of the order of 10 million years toward extreme mass ratios but that none of the models has a sufficiently large masstransfer rate to account for the rapid period changes observed in W UMa systems. A sequence of evolved models is also computed, and it is shown that any of the zeroage models could be a possible progenitor of any of the evolved models if the total mass and angular momentum remain constant and if the equipotential can move freely between the inner and outer critical surfaces. The problem of contact breaking is briefly considered.
 Publication:

Astronomy and Astrophysics
 Pub Date:
 April 1977
 Bibcode:
 1977A&A....56...99R
 Keywords:

 Binary Stars;
 Stellar Evolution;
 Stellar Luminosity;
 Stellar Models;
 Angular Momentum;
 Astronomical Models;
 Distribution Functions;
 Equipotentials;
 Galactic Clusters;
 Mass Transfer;
 Stellar Envelopes;
 Astrophysics