Kinematics of the chromospherically active binaries and evidence of an orbital period decrease in binary evolution

Kinematics of 237 Chromospherically Active Binaries (CAB) were studied. The sample is heterogeneous with different orbits and physically different components from F to M spectral type main sequence stars to G and K giants and super giants. The computed U , V , W space velocities indicate the sample is also heterogeneous in the velocity space. That is, both kinematically younger and older systems exist among the non-evolved main sequence and the evolved binaries containing giants and sub giants. The kinematically young (0.95 Gyr) sub-sample (N=95), which is formed according to the kinematical criteria of moving groups, was compared to the rest (N=142) of the sample (3.86 Gyr) in order to investigate observational clues of the binary evolution. Comparing the orbital period histograms between the younger and older sub-samples, evidences were found supporting Demircan’s (1999) finding that the CAB binaries lose mass (and angular momentum) and evolve towards shorter orbital periods. The evidence of mass loss is noticeable on the histograms of the total mass (Mh + Mc), which is compared between the younger (available only N=53 systems) and older subsamples (available only N=66 systems). The orbital period decrease during binary evolution is found to be clearly indicated by the kinematical ages of 6.69, 5.19, and 3.02 Gyr which were found in the sub samples according to the period ranges of logP ≤ 0.8, 0.8 < logP ≤ 1.7, and 1.7 < logP ≤ 3 among the binaries in the older sub sample.