Yazar "Demircan, Oya" seçeneğine göre listele

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    Age Dependent Angular Momentum, Orbital Period and Total Mass of Detached Binaries
    (Cambridge Univ Press, 2012) Demircan, Oya; Tüysüz, Mehmet; Soydugan, Faruk; Bilir, Selçuk
    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 (3) 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 (3), orbital period (13), 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.
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    Kinematic Properties of Chromospheric Active Binary Stars
    (Cambridge Univ Press, 2012) Tüysüz, Mehmet; Soydugan, Faruk; Bilir, S.; Demircan, Oya
    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 Eggen's 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.
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    O-C Analysis of Selected 3-Body Systems
    (Cambridge Univ Press, 2012) Ogloza, W.; Kreiner, J. M.; Stachowski, G.; Winiarski, M.; Zakrzewski, B.; Doğru, Serkan; Aliçavuş, Fahri; Demircan, Oya; Erdem, Ahmet
    This paper presents the results of the analysis of (O-C) diagrams of four eclipsing variables. The diagrams are based on times of minima collected in the Cracow database, which contains times of minima found in the literature, from observations at Mt. Suhora and Ulupinar Observatories, or determined using publicly-available photometric surveys (NSVS, ASAS etc).
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    The Catalogue of Stellar Parameters from the Detached Double-Lined Eclipsing Binaries in the Milky Way
    (Cambridge Univ Press, 2014) Eker, Z.; Bilir, Selçuk; Soydugan, Faruk; Yaz Gökçe, Esma; Soydugan, Esin; Tüysüz, Mehmet; Şenyüz, Tunç; Demircan, Oya
    The most accurate stellar astrophysical parameters were collected from the solutions of the light and the radial velocity curves of 257 detached double-lined eclipsing binaries in the Milky Way. The catalogue contains masses, radii, surface gravities, effective temperatures, luminosities, projected rotational velocities of the component stars, and the orbital parameters. The number of stars with accurate parameters increased 67% in comparison to the most recent similar collection by Torres, Andersen, & Gimenez (2010). Distributions of some basic parameters were investigated. The ranges of effective temperatures, masses, and radii are 2 750 < T-eff (K)< 43 000, 0.18 < M/M-circle dot < 33, and 0.2 < R/R-circle dot < 21.2, respectively. Being mostly located in one kpc in the Solar neighborhood, the present sample covers distances up to 4.6 kpc within the two local Galactic arms, Carina-Sagittarius and Orion Spur. The number of stars with both mass and radius measurements better than 1% uncertainty is 93, better than 3% uncertainty is 311, and better than 5% uncertainty is 388. It is estimated from the Roche lobe filling factors that 455 stars (88.5% of the sample) are spherical within 1% of uncertainty.