Yazar "Karatas, Y." seçeneğine göre listele

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    Öğe
    Dynamical evolution of active detached binaries on the log Jo-log M diagram and contact binary formation
    (Blackwell Publishing, 2006) Eker, Z.; Demircan, O.; Bilir, S.; Karatas, Y.
    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.
  • [ X ]
    Öğe
    Evidences on secular dynamical evolution of detached active binary orbits and contact binary formation
    (Astronomical Soc Pacific, 2007) Eker, Z.; Demircan, O.; Bilir, S.; Karatas, Y.
    Evidence of secular dynamical evolution for detached active binary orbits are presented. First order decreasing rates of orbital angular momentum (OAM), systemic mass (M = M-1 + M-2) and orbital period of detached active binaries have been determined a J/J = 3.48 x 10(-10)yr(-1),M/M = 1.30 x 10(10)yr(-1) and P/P 3.96 x 10(-10)yr(-1) from the kinematical ages of 62 field detached systems. The ratio of d log J/ d log M = 2.68 implies that either there are mechanisms which amplify AM loss delta = 2.68 times with respect to isotropic AM loss of hypothetical isotropic winds or there exist external causes contributing AM loss in order to produce this mean rate of decrease for orbital periods. Various decreasing rates of OAM (d log J /dt) and systemic mass (d log M /dt) determine various speeds of dynamical evolutions towards a contact configuration. According to average dynamical evolution with delta = 2.68, the fraction of 10, 22 and 39 per cent of current detached sample is expected to be contact system within 2, 4 and 6 Gyr respectively.