We 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.

Orbital angular momentum (OAM, Jo), 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 and log Jo–log M were formed from 119 CAB and 102 W UMa stars. The log Jo–log 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 Jo–log M diagram. Since the orbital size (a) and period (P) of binaries are determined by their current Jo, M and mass ratio, q, the rates of OAM loss (d log Jo/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 Jo–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 Jo 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.

Calibrations are presented here for metallicity ([Fe/H]) in terms of the ultraviolet excess, [δ(U−B) at B−V= 0.6, hereafter δ0.6], and also for the absolute visual magnitude (MV) and its difference with respect to the Hyades (ΔMHV) in terms of δ0.6 and (B−V), making use of high‐resolution spectroscopic abundances from the literature and Hipparcos parallaxes. The relation [Fe/H]–δ0.6 has been derived for dwarf plus turn‐off stars, and also for dwarf, turn‐off, plus subgiant stars classified using the MV–(B−V)0 plane of Fig. 11, which is calibrated with isochrones from Bergbusch & VandenBerg (and also VandenBerg & Clem). The [Fe/H]–δ0.6 relations in our and agree well with those of Carney, as can be seen from Fig. 5(a). Within the uncertainties, the zero‐points, +0.13(±0.05) of and +0.13(±0.04) of , are in good agreement with the photometric ones of Cameron and of Carney, and close to the spectroscopic ones of Cayrel et al. and of Boesgaard & Friel for the Hyades open cluster. Good quantitative agreement between our estimated [Fe/H] abundances with those from uvby–β photometry and spectroscopic [Fe/H]spec values demonstrates that our can be used in deriving quality photometric metal abundances for field stars and clusters using UBV data from various photometric surveys. 11 M V − (B−V)0 for the 514 stars in our sample to which the Lutz–Kelker corrections have been applied. Solid lines show the isochrones for the range of −2.31 ≤[Fe/H]≤−0.30. The 12‐Gyr isochrones of BV& VC with [α/Fe]=+0.30 for [Fe/H]≤−0.60 and with [α/Fe]= 0.00 for [Fe/H] > −0.60 have been used. Stars which fall in between the dashed lines are assumed to be subgiant stars. Stars which lie below and to the left‐hand side of the lower dashed line are classified as turn‐off and dwarf stars for the range of −2.31 ≤[Fe/H]≤−0.30. Stars between the dashed lines which lie to the left‐hand side of the [Fe/H]=−2.31 isochrone are included in this work as subgiants. Stars to the right‐hand side of the [Fe/H]=−0.30 isochrone and below the lower dashed line are included as turn‐off and dwarf stars. The 42 stars above the upper dashed line are excluded from this work as probable giant stars on the basis of these isochrones. 5 (a) The relation of [Fe/H]spec−δ0.6 from the binning of the dependent variable shown in Figs 3(a) and 4(a). and are plotted as filled dots (subgiant, dwarf, plus turn‐off stars) and plus signs (dwarf plus turn‐off stars), respectively. Solid and dashed lines show the relations from Carney (1979) and Cameron (1985), respectively. Open triangles plot the relation of Sandage & Fouts (1987), and the synthetic relation of Buser & Kurucz (1992) is shown with diamond symbols. The relations of and are close to that of Carney (1979). Note that the zero‐point, [Fe/H]spec for δ0.6= 0.0, of Sandage & Fouts (1987) is larger than the others. (b) The relation of [Fe/H]spec−δ0.6 from the binning of the independent variable shown in Figs 6(a) and 7(a). and are plotted as filled dots (subgiant, dwarf plus turn‐off stars) and plus sig...

The 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 (Mh+Mc), 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≤ 0.8, 0.8 < log P≤ 1.7 and 1.7 < log P≤ 3, respectively, among the binaries in the older subsample.

Abstract:We have taken 88 dwarfs, covering the colour-index interval 0.37 ≤ (B−V) 0 ≤ 1.07 mag, with metallicities −2.70 ≤ [Fe/H] ≤+ 0.26 dex, from three different sources for new metallicity calibration. The catalogue of Cayrel de Strobel et al. (2001), which includes 65% of the stars in our sample, supplies detailed information on abundances for stars with determination based on high-resolution spectroscopy. In constructing the new calibration we have used as 'corner stones' 77 stars which supply at least one of the following conditions: (i) the parallax is larger than 10 mas (distance relative to the Sun less than 100 pc) and the galactic latitude is absolutely higher than 30 • ; (ii) the parallax is rather large, if the galactic latitude is absolutely low and vice versa. Contrary to previous investigations, a third-degree polynomial is fitted for the new calibration: [Fe/H] = 0.10 − 2.76δ − 24.04δ 2 + 30.00δ 3 . The coefficients were evaluated by the least-squares method, without regard to the metallicity of Hyades. However, the constant term is in the range of metallicity determined for this cluster, i.e. 0.08 ≤ [Fe/H] ≤ 0.11 dex. The mean deviation and the mean error in our work are equal to those of Carney (1979)