Evidences on secular dynamical evolution of detached active binary orbits and contact binary formation

Abstract

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 as $\dot J/J = -3.48 \times 10^{-10}$yr$^{-1}$, $\dot M/M = -1.30 \times 10^{-10}$yr$^{-1}$ and $\dot P/P = -3.96\times 10^{-10}$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 11, 23 and 39 per cent of current detached sample is expected to be contact system within 2, 4 and 6 Gyr respectively.