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Öğe Kinematics of chromospherically active binaries and evidence of an orbital period decrease in binary evolution(Oxford Univ Press, 2004) Karatas, Y; Bilir, S; Eker, Z; Demircan, OThe kinematics of 237 chromospherically active binaries (CABs) 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 supergiants. The computed U, V, W space velocities indicate that the sample is also heterogeneous in velocity space. That is, both kinematically younger and older systems exist among the non-evolved main sequence and the evolved binaries containing giants and subgiants. The kinematically young (0.95 Gyr) subsample (N = 95), which is formed according to the kinematical criteria of moving groups, was compared with the rest (N = 142) of the sample (3.86 Gyr) to investigate any observational clues of binary evolution. Comparing the orbital period histograms between the younger and older subsamples, evidence was found supporting the finding of Demircan that the CABs 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 (M-h + M-c), which is compared between the younger (only N = 53 systems available) and older subsamples (only N = 66 systems available). 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 subsamples according to the period ranges of log P less than or equal to 0.8, 0.8 < log P <= 1.7 and 1.7 < log P less than or equal to 3, respectively, among the binaries in the older subsample.Öğe Kinematics of W Ursae Majoris type binaries and evidence of the two types of formation(Oxford Univ Press, 2005) Bilir, S; Karatas, Y; Demircan, O; Eker, ZWe study the kinematics of 129 W UMa binaries and we discuss its implications on the contact binary evolution. The sample is found to be heterogeneous in the velocity space. That is, kinematically younger and older contact binaries exist in the sample. A kinematically young (0.5 Gyr) subsample (moving group) is formed by selecting the systems that satisfy the kinematical criteria of moving groups. After removing the possible moving group members and the systems that are known to be members of open clusters, the rest of the sample is called the field contact binary (FCB) group. The FCB group is further divided into four groups according to the orbital period ranges. Then, a correlation is found in the sense that shorter-period less-massive systems have larger velocity dispersions than the longer-period more-massive systems. Dispersions in the velocity space indicate a 5.47-Gyr kinematical age for the FCB group. Compared with the field chromospherically active binaries (CABs), presumably detached binary progenitors of the contact systems, the FCB group appears to be 1.61 Gyr older. Assuming an equilibrium in the formation and destruction of CAB and W UMa systems in the Galaxy, this age difference is treated as an empirically deduced lifetime of the contact stage. Because the kinematical ages (3.21, 3.51, 7.14 and 8.89 Gyr) of the four subgroups of the FCB group are much longer than the 1.61-Gyr lifetime of the contact stage, the pre-contact stages of the FCB group must dominantly be producing the large dispersions. The kinematically young (0.5 Gyr) moving group covers the same total mass, period and spectral ranges as the FCB group. However, the very young age of this group does not leave enough room for pre-contact stages, and thus it is most likely that these systems were formed in the beginning of the main sequence or during the pre-main-sequence contraction phase, either by a fission process or most probably by fast spiralling in of two components in a common envelope.Öğe Mass loss and orbital period decrease in detached chromospherically active binaries(Blackwell Publishing, 2006) Demircan, O; Eker, Z; Karatas, Y; Bilir, SThe secular evolution of the orbital angular momentum (OAM), the systemic mass (M = M-1 + M-2) and the orbital period of 114 chromospherically active binaries (CABs) were investigated after determining the kinematical ages of the subsamples which were set according to OAM bins. OAMs, systemic masses and orbital periods were shown to be decreasing by the kinematical ages. The first-order decreasing rates of OAM, systemic mass and orbital period have been determined as J = 3.48 x 10-(10) yr(-1) per systemic OAM, M = 1.30 x 10-(10) yr(-1) per systemic mass and p = 3.96 x 10(-10) yr(-1) per orbital period, respectively, from the kinematical ages. The ratio of d log J/d log M = 2.68, which were derived from the kinematics of the present sample, implies that there must be a mechanism which amplifies the angular momentum loss (AML) (A) over bar = 2.68 times in comparison to isotropic AML of hypothetical isotropic wind from the components. It has been shown that simple isotropic mass loss from the surface of a component or both components would increase the orbital period.
