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Öğe A near-contact binary(Wiley-V C H Verlag Gmbh, 2005) Çiçek, C; Erdem, A; Soydugan, FNew BVR light curves and photometric analysis of the eclipsing binary star CN And are presented. The shape of the light curves are typical of beta Lyr type, and there are large asymmetries between maxima. The BVR light curves and the radial velocity curves (from Rucinski et al. 2000) were solved with the Wilson-Devinney method, simultaneously. The results suggest that CN And is a almost contact binary system, in which the component stars are filling similar to 99% of their Roche lobes. We discuss the model with a large dark starspot on the more massive star and a bright substellar spot on the companion to account for the light curve asymmetries. The absolute parameters of the system were also derived. The system resembles the near contact binary V1010 Oph according to its Roche configuration and light curve asymmetries. We, also, discuss the evolution of the system: it seems to be in a transition phase to the contact era. All previous times of minimum light were collected and combined with the new ones presented in this work. The variation of the orbital period of the system was then analyzed. The results reveal that the orbital period has a secular decrease of about 1.98 +/- 0.04 sec per century, which corresponds to a conservative mass transfer from the more to the less massive component at a rate of (1.52 +/- 0.09) x 10(-7)m(circle dot)/yr or a mass loss from the primary component due to magnetic stellar winds at a rate of (7.83 +/- 0.09) x 10(-8)m(circle dot)/yr.Öğe A new photometric study of CW Cephei and its apsidal motion(Wiley-V C H Verlag Gmbh, 2004) Erdem, A; Soydugan, E; Soydugan, F; Özdemir, S; Çiçek, C; Bulut, I; Demircan, ONew photoelectric observations of the eccentric orbit binary CW Cephei have been carried out in B, V and R colours during the 2000 observing season at TUBITAK (The Scientific and Technical Research Council of Turkey) National Observatory. The light curves of the system were analyzed with a nonsynchronous rotation approach using the method of Wilson-Devinney in B, V and R bands, simultaneously. Especially, we used the R band to check for a third light in the solution as distinct from previous studies. But, the third light contribution in the light curves comes out to be almost negligible. In this study, the values of the longitude of periastron (omega) of the system's orbit found in the solutions of the light curves and radial velocity curves were collected and the variation of w with time was investigated. A new value of the apsidal motion velocity has been obtained as omega=0.0582 +/- 0.0011 (deg/cycle), corresponding to an apsidal period U=46 +/- 1 yr.Öğe A photometric study of the near contact binary star GK Cep(Wiley-V C H Verlag Gmbh, 2001) Erdem, APhotoelectric observations of the eclipsing binary GK Cep (BV 382) have been carried out in B and V colors at the Ege University Observatory. Using the (O-C) residuals formed by the photoelectric minima times, an orbital period study of the system was performed. It is confirmed that the sinusoidal (O-C) variation corresponds to a secular period change caused by the light time effect due to an unseen third body in the system. The observed photoelectric light curves of the system were analyzed with the methods of Wilson-Devinney. Simultaneous solutions were made using the radial velocity curves of Bartolini et al. (1965). The system was found to be detached, but not far from the contact phase. The absolute parameters of the system were also deduced. Both compronents are on the Main Sequence.Öğe A photometric study of the recently discovered eclipsing binary V899 Herculis(E D P Sciences, 2002) Özdemir, S; Demircan, O; Erdem, A; Çiçek, C; Bulut, I; Soydugan, E; Soydugan, FThe radial velocity and UBV light curves of V899 Her as found in the literature were studied for the first time to obtain the orbital parameters and geometry of the system. The solutions obtained by using the Wilson-Devinney code reveal an over-contact system with a fill-out factor of 23.7%. This solution is only possible with a large amount of third light (L-3 approximate to 0.68) which confirms the spectroscopic result obtained by Lu et al. (2001) who reported that the system of which V899 Her is a fainter component is triple, or even quadruple. The distance of the system found by using absolute parameters is comparable with the Hipparcos result.Öğe Astrometric solution of the multiple system XY Leo(Springer, 2005) Bakis, V; Erdem, A; Budding, E; Demircan, O; Bakis, HAn astrometric solution, together with time of minimum analysis, has been made for the multiple system XY Leonis (HIP 49136) to identify the properties of the remote companion to the eclipsing pair (AB). From this solution, we derive the inclination of the wide orbit (AB-cd) as 94.4 degrees +/- 0.2 degrees, angle of nodes as 247.3 degrees +/- 0.2 degrees, and the mass of the wide component (the dwarf binary cd) as 0.98 +/- 0.2 M-.. This study confirms that the light travel time effect can explain the sinusoidal O - C variation of the eclipsing system.Öğe Catalogue of Algol type binary stars(Edp Sciences S A, 2004) Budding, E; Erdem, A; Çiçek, C; Bulut, I; Soydugan, F; Soydugan, E; Bakis, VA catalogue of (411) Algol-type (semi-detached) binary stars is presented in the form of five separate tables of information. The catalogue has developed from an earlier version by including more recent information and an improved layout. A sixth table lists (1872) candidate Algols, about which fewer details are known at present. Some issues relating to the classification and interpretation of Algol-like binaries are also discussed.Öğe Multi-facility study of the Algol-type binary ? Librae(Springer, 2005) Budding, E; Bakis, V; Erdem, A; Demircan, O; Iliev, L; Iliev, I; Slee, OBVarious branches of observational information, and related physical problems concerning the bright, relatively close, Algol binary 8 Lib are discussed. Times of minimum light confirm the classical Algol status, which, combined with the optical and IR photometry of Lazaro et al. (2002), provide the basis for a good understanding of the system's basic parameters. New spectroscopy from the Coude spectrograph of the Rozhen Observatory (Bulgaria) allows further information on the model and the mass transfer process. Very high resolution radio observations would also have much to reveal about astrophysics of the semi-detached configuration, not only directly, by informing about the outermost envelopes of the components, but indirectly through high accuracy positional information. We show how this may be related to careful period and astrometric studies. delta Lib thus provides a rich source of information on the astrophysics of the Algol configuration.Öğe Photometric analysis of the eclipsing binary star AI Draconis(Edp Sciences S A, 2000) Degirmenci, ÖL; Gülmen, Ö; Sezer, C; Erdem, A; Devlen, ANew photometric data from the eclipsing binary star AI Draconis has been analyzed with the method of Wilson-Devinney. The system shows a period increase of about 0.91 sec per century, which corresponds to amass transfer from the less to the more massive component at a rate of 7.5 10(-7) M./yr under the conservative mass transfer hypothesis. We also suggest that the system has an unseen component which orbits around the mass center of the triplet system with a period of about 23 yrs. We found that the projectional angular separation between the third star and eclipsing pair varies from 0. 048 to 0. 235. These results suggestive of a third body should be checked in the future with more sensitive observations.Öğe Photometric solution of the eclipsing binary system EF Bootis(Wiley-V C H Verlag Gmbh, 2004) Özdemir, S; Demircan, O; Çiçek, C; Erdem, AThe EF Boo eclipsing binary system is studied in the context of optical light curves and radial velocity curves published in the literature. The best-solution leads to an over-contact configuration of W-subclass of W UMa systems with a fill-out factor of 28%. Absolute parameters based on simultaneous solution of light and radial velocity curves are presented.Öğe Photometric study of the active binary star V1430 Aquilae(Wiley-V C H Verlag Gmbh, 2006) Erdem, A; Sürgit, DNew BVR light curves and a photometric analysis of the eclipsing binary star V1430 Aql are presented. The light curves were obtained at the Canakkale Onsekiz Mart University Observatory in 2004. The light curves are generally those of detached eclipsing binaries, but there are large asymmetries between maxima. New BVR light curves were analysed with an ILOT procedure. Light curve asymmetries of the system were explained in terms of large dark starspots on the primary component. The primary star shows a long-lived and quasi-poloidal spot distribution with active longitudes in opposite hemispheres. Absolute parameters of the system were derived. We also discuss the evolution of the system: the components are likely to be pre-main sequence stars, but a post-main sequence stage cannot be ruled out. More observations are needed to decide this point. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.Öğe Photometric study of the binary system V397 cephei(Oxford Univ Press, 2005) Bulut, I; Demircan, O; Budding, E; Erdem, A; Çiçek, C; Esenoglu, H; Soydugan, FThe first ground-based UBV observations (2001, Inf. Bull. Variable Stars, 5129) of V397 Cep were analyzed by using the Wilson-Devinney method, and the results were compared with others in the literature. A consistent geometry with a photometric mass-ratio close to unity and an eccentric orbit of e similar or equal to 0.13 was found. The longitude of the periastron (omega) was found significantly different for two different light curves, which is strongly suggestive of an apsidal motion with a period of about 300 yr. This makes V397 Cep an important candidate for studies of apsidal motion.Öğe The close binary system EG cephei(Wiley-V C H Verlag Gmbh, 2005) Erdem, A; Budding, E; Demircan, O; Degirmenci, OL; Gülmen, Ö; Sezer, CNew light curves and available times of minima of a beta Lyr system EG Cep were analysed to deduce more information on the nature of the system. The main U-shaped (O - C) variation was interpreted in terms of the mass transfer and mass loss in the system. The same variation was also considered as a part of a sinusoidal variation and thus interpreted in terms of a light-time effect due to an unseen component in the system. New B and V light curves were analyzed with different fitting procedures, and there is general agreement that both stars must be very close to each other and to stability limits. A model that fits all the data well has a near main sequence primary and a secondary star that is overflowing matter towards it. This secondary is also reasonably close to main sequence conditions. The configuration thus appears to be a (relatively uncommon) ' Case A ' type evolving Algol and raises interesting questions about such interactive evolution and potentially useful tests of theory.Öğe The early type contact binary system V 382 Cygni(E D P Sciences, 1999) Degirmenci, ÖL; Sezer, C; Demircan, O; Erdem, A; Özdemir, S; Ak, H; Albayrak, BNew photometric data set of the early type contact binary V382 Cyg have been analyzed with emphasis on determining the photometric mass ratio of the system. The result (q = 0.68) supports the value given by Popper & Hill (1991). A study of the system using new data shows a period increase of about 3.28 s per century, which corresponds to a very large rate similar to 5.0 10(-6) M./yr of mass transfer from the less massive to the more massive component under the conservative mass transfer hypothesis.Öğe The light and period changes of RT Andromedae(Edp Sciences S A, 2001) Erdem, A; Demircan, O; Güre, MThe nature of the long-term orbital period variation and the light level variation of RT And was studied based on all available photometric observations. The (O-C) diagram formed by all available times of eclipse minima could be either of a quasi-sinusoidal form superimposed on a parabolic form, or a long period sinusoidal form. The quasi-sinusoidal form with an amplitude of similar to0.002 days and a period of similar to 65 years could be due to a cyclic magnetic activity modulation on the orbital period of the system. Applegate's theory (Applegate 1992), in this case, predicts an similar to3 kG mean subsurface magnetic field for the primary component of the system. The parabolic form corresponds to a secular period decrease of about 3 x 10(-9) m(circle dot) yr(-1) caused by mass loss from the system, and the long-period sinusoidal form with an amplitude of similar to0.02 days and a period of similar to 105 years corresponds to a secular period change caused by the light-time effect due to an unseen third star in the system. It was estimated that the unseen third star should be a low mass (lower than 0.6 m(circle dot)) and faint (similar to5.(m) fainter than the system RT And) star, whose detection is almost impossible. Future data will add information on the nature of the secular (O-C) variation. Secular light level variation of the system was found to be irregular and no correlation was detected with the orbital period variation.Öğe The orbital period study and photometric analysis of XY Ursae Majoris(Edp Sciences S A, 1998) Erdem, A; Gudur, NPhotoelectric observations of the eclipsing binary XY UMa have been carried out in B and V colours at the Ege University Observatory. Combining these newly obtained data with the previous ones available in the literature, the problem pertaining to the orbital period of the system has been investigated through a detailed description of the O-C diagram. The sinusoidal and secular changes have been found. Such variations of the orbital period have been examined in terms of three plausible mechanisms, namely (i) a light-time effect due to a third body, (ii) the orbital period modulation due to magnetic activity cycle of a component star, and (iii) a mass loss case in which the ejected material escapes out from the binary system. A combination of a magnetic activity cy de mechanism and a mass loss case is found to reproduce satisfactorily the period changes. Further, the observed photoelectric light curves of the system have been analyzed with the Wilson-Devinney approach. This analysis shows that the asymmetries of the light curves of XY UMa can be interpreted in terms of cool star-spot covering 7% of the stellar photosphere of the primary component of this binary. The system is found to be a beta Lyrae type detached binary. The absolute elements of the system are also deduced.Öğe Third body problem in the eclipsing binary star TV Cassiopeia(Springer, 2002) Erdem, AThe aim of this work is to search for some evidences for the presence of unseen companion(s) in the eclipsing binary star TV Cassiopeia using its O-C diagram. Assuming that the light-time effect is responsible for the periodic components on the O-C diagram, the set of orbital parameters were derived using Irwin's (1959) method. The resulting orbital parameters and mass of the hypothetical third body are physically acceptable. Lacking other proofs of the third body presence, however, the hypothesis can be treated as a probable case only.
