Oktay Demircan

UBV Photometry of the Massive Eclipsing Binary TT Aur

UBV observations carried out mainly at the Turkish National Observatory (TUG) and the collected times of eclipse minima of the massive eclipsing binary TT Aur were used to study the system parameters. The simultaneous solution of the light curves by Wilson-Devinney (1992) code yields a semi-detached configuration with slightly larger Roche-lobe filling secondary. The shoulders of primary minimum indicate some excess absorption probably due to circumstellar material in the form of partial disk around the primary component. The deeper primary minimum in U filter can be an indication of a hotter region on the facing hemisphere of the primary. The period variation of the system reveals the existence of a possible third component star in a circular orbit around the system.

Age Dependent Angular Momentum, Orbital Period and Total Mass of Detached Binaries

The orbital angular momenta OAM (J) of detached binaries (including both cool and hot binaries) were estimated and nine subgroups were formed according to their OAM (J) distribution. The mean kinematical ages of all subgroups have been estimated by using their space velocity distributions and, thus, the age dependent variations of the mean OAM (J), orbital period (P), and total mass (M) of all subgroups were investigated. It was discovered that: i) The orbital period of detached binaries with radiative components decrease very slowly during the main sequence (MS) evolution. It is interesting that the large amount of mass loss is almost balanced by the OAM loss, and not much change in the orbital periods is observed. ii) The nuclear evolution of radiative components beyond the MS initiates the increase of the periods until the components have convective upper layers, i.e. until they become later than F5 IV, and the system becomes a cool binary with sub-giant or giant components. iii) The large co-rotating distance of the magnetically-driven wind in cool binaries (CAB) carries out a large amount of OAM and then the periods of such binaries decrease significantly, and the orbits shrink until another effect such as mass transfer dominates the period changes.

Kinematic Properties of Chromospheric Active Binary Stars

The kinematic behaviour of 362 chromospherically active binary stars (CABs) in the solar neighbourhood were investigated. The Third CABs Catalog by Eker et al . (2008) was used as the main source. The spatial distribution and the components of the Galactic space velocities of the programme stars were determined. The effects of differential rotation and Local Standard of Rest (LSR) were corrected for all systems. Forty probable moving group (MG) members were determined by Eggens criteria. The kinematic age of the young systems, which are probable members of MGs, was calculated as 0.79 (0.21) Gyr and the rest of 322 field stars were found to have a kinematic age of 4.38 (1.1) Gyr. Field CABs were separated into two sub-groups: dwarf systems, which were formed by main sequence (dwarf) stars, and evolved systems included at least one evolved (giant or sub-giant) component. The kinematic age of 134 dwarf systems was calculated as 4.69 (0.75) Gyr and 4.15 (1.29) Gyr for 188 evolved CABs.

Photometry of Some Close Binaries at the Ankara University Observatory

Three close binary systems YY Eri, V456 Oph and AW Peg are discussed on the basis of UBV photoelectric observations carried out at the Ankara University Observatory in 1988 and 1989.