Dynamical evolution of active detached binaries on the log J(o)-log M diagram and contact binary formation

Eker Z., Demircan O., Bilir S., Karatas Y.

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, vol.373, no.4, pp.1483-1494, 2006 (SCI-Expanded) identifier identifier

  • Publication Type: Article / Article
  • Volume: 373 Issue: 4
  • Publication Date: 2006
  • Doi Number: 10.1111/j.1365-2966.2006.11073.x
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Page Numbers: pp.1483-1494
  • Keywords: binaries : spectroscopic, stars : evolution, stars : mass-loss, ANGULAR-MOMENTUM LOSS, ORBITAL PERIOD DECREASE, DISK POPULATION, STELLAR GROUPS, TRIPLE STARS, SYSTEMS, KINEMATICS
  • Istanbul University Affiliated: Yes


Orbital angular momentum (OAM, J(o)), systemic mass (M) and orbital period (P) distributions of chromospherically active binaries (CAB) and W Ursae Majoris (W UMa) systems were investigated. The diagrams of logJ(o)-IogP, logM-logP and logJ(o)-IogM were fortned from 119 CAB and 102 W UMa stars. The log J(o)-Iog M diagram is found to be most meaningful in demonstrating dynamical evolution of binary star orbits. A slightly curved borderline (contact border) separating the detached and the contact systems was discovered on the log J(o)-Iog M diagram. Since the orbital size (a) and period (P) of binaries are determined by their current J(o), M and mass ratio, q, the rates of OAM loss (d log J(o)/dt) and mass loss (d log M/dt) are primary parameters to determine the direction and the speed of the dynamical evolution. A detached system becomes a contact system if its own dynamical evolution enables it to pass the contact border on the log J(o)-log M diagram. The evolution of q for a mass-losing detached system is unknown unless the mass-loss rate for each component is known. Assuming q is constant in the first approximation and using the mean decreasing rates of J(o) and M from the kinematical ages of CAB stars, it has been predicted that 11, 23 and 39 per cent of current CAB stars would transform to W UMa systems if their nuclear evolution permits them to live 2, 4 and 6 Gyr, respectively.