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Öğe A binary star with a ? Scuti component(Univ Chicago Press, 2003) Soydugan, E; Demircan, O; Akan, MC; Soydugan, FNew photometric observations of the Algol-type binary system AB Cassiopeiae were obtained in B and V filters during the 2001-2002 observing season at Ege University Observatory. As expected, the new light curves of the system, which were analyzed using the Wilson-Devinney code, exhibit short-period oscillations due to pulsation of the primary component. A photometric q-value search was performed, and the mass ratio of the system was found to be 0.19. The residuals from the observed-minus-computed light curves of the system reveal the pulsation light curves of the primary component. From the clear cycles of the pulsations in the light curves, we determined 21 new times of maximum light. The frequency content was investigated by using the Period98 program. Although the amplitude variation may suggest multiple periodicity in the pulsations, the power spectrum shows that only one frequency is significant; the remaining frequencies are probably not statistically significant. A multisite campaign is needed in order to study the reliability of the other pulsation modes.Öğe A light and period study of SV Camelopardalis(Edp Sciences S A, 2001) Albayrak, B; Demircan, O; Djurasevic, G; Erkapic, S; Ak, HNew BVR light curves and times of minimum light for the short period RS CVn system SV Cam were analysed to derive the physical parameters of the system and the parameters of the third body orbit. The light curves obtained at the TUBITAK National Observatory during two nights in 2000 show considerable asymmetry and night-to-night variations. The analysis of the light curves is made using Djurasevic's inverse problem method. The Roche model with spotted areas on the hotter primary component yields a good fit to observations. The extensive series of published photoelectric minima times indicate that the eclipsing pair orbits around the common mass center of the triple system with a period of 41.32 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 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 Apsidal motion and photometric elements of the eccentric eclipsing binary V401 lacertae(Oxford Univ Press, 2006) Bulut, I; Demircan, ONew UBV photometric observations of the recently discovered eccentric orbit binary V401 Lacertae were analyzed by using the Wilson-Devinney program. Seven new minimum times were estimated by using new observations. The analysis of the light Curves and all available minimum time,, has revealed that the system is detached, with the orbital eccentricity e = 0.1734 +/- 0.0003, the longitude of the periastron omega = 63 degrees 93 +/- 0 degrees 15, the rate of change of the longitude of periastron omega 0.degrees 0200 +/- 0.degrees 0024 cycle(-1), corresponding to ail apsidal motion period of U=96.2 +/- 11.4yr. The apsidal motion of the system has been confirmed by the significant difference oil the longitude of periastron (omega) obtained from two light Curves (Hipparcos and ourselves) in two different epochs.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 Basic functions of the light curve analysis of eclipsing variables in the frequency domain(Springer, 2005) Demircan, OAn analytically tractable method of transforming the problem of light curve analysis of eclipsing binaries from the time domain into the frequency domain was introduced by Kopal (1975, 1979, 1990). This method uses a new general formulation of eclipse functions alpha, the so-called moments A(2m), and their combinations as g(2m) = A(2m+2)/(A(2m)A(2m+4)) functions for the basic spherical model. In this paper, I will review the use of these functions in the light curve analysis of eclipsing binaries.Öğe Chemical analysis of some meteorite claims in Turkey(IEEE, 2005) Sengül, E; Kocahan, O; Özmaya, S; Özel, ME; Demircan, OWe have carried out chemical analysis work on some meteorite and meteorite candidates found in Turkey. Major and minor element abundances of samples are used to decide on the nature of claimed stones. Results are also compared with the literature. A need for a national meteorite inventory and data base is highlighted and its possible uses are mentioned.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.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 Orbital period changes of ALGOL-type binaries: S Equulei and AB Cassiopeiae(Univ Chicago Press, 2003) Soydugan, F; Demircan, O; Soydugan, E; Ibanoglu, CThe orbital periods of two Algol-type binaries, S Equ and AB Cas, are studied based on all available times of minima. It is found that the O-C variations of both systems can be represented by a parabolic and a periodic term. S Equ has an accretion region due to mass transfer as shown by Richards and coworkers and Richards & Albright. On the other hand, Zola obtained a light-curve solution with a third light. Our study reveals evidence of mass transfer and third component stars in both systems. The parabolic terms in the O-C variations are due to mass transfer from less massive to more massive components, which is consistent with the semidetached nature of both systems. The periodic terms are explained with the additional third stars in the systems. It is interesting that there is no sign of a magnetic braking effect from the cool secondary in the O-C variation of either system.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 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 Refinement of third body parameters and new photometric results for the early-type multiple system IU Aurigae(E D P Sciences, 2003) Özdemir, S; Mayer, P; Drechsel, H; Demircan, O; Ak, HThe massive eclipsing binary system IU Aurigae is re-analyzed in the context of new photometric observations and an improved treatment of its long-term period changes (O-C diagram) derived from new times of minima. The best-fit of the O-C curve reveals that the third component is orbiting around the system with a period of 293.3 days in a highly eccentric orbit (e = 0.62). A solution of the most recent UBV light curves obtained during 1997/1998 showed a third light contribution of approximate to23% and continuation of the orbital plane precession of IU Aurigae. Since the revised mass of the third component deduced from the analysis of the O-C curve of m(3) = 14.2 M-. would imply a larger fraction of third light than suggested by the value of 23% derived from the light curve analysis, the third body is possibly composed of two components. A q-search test applied to the UBV light curves yields a minimum chi(2) value at q = 0.67 +/- 0.02, which confirms previous photometric and spectroscopic solutions.Öğe The 150D modulation of the X-ray emission of CYG X-1(Kluwer Academic Publ, 2001) Özdemir, S; Demircan, OThe X-ray observations of Cyg X-1, covering a period of 3.8 years, by the All Sky Monitor (ASM) on board the Rossi X-ray Timing Explorer (RXTE) were analysed to search for long periodicities. The periodicities in the original data were seen to be distorted by the high/soft state and the failed state counts of the system, and thus the power spectra showed two unrealistic peaks at 1608 and 406 days. The similar to 300 day modulation reported previously (e.g. Priedhorsky et al. 1983) is not confirmed by the present ASM data. Truncation of the high counts above 30 cnts/s partly eliminates the distortion and reveals the true period of 150(d) in the power spectra. It is interesting that the high/soft state (HS) and the failed state transitions (FST) always occur on the maximum phase of the 150(d) cycle.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 connection between the pulsational and orbital periods for eclipsing binary systems(Oxford Univ Press, 2006) Soydugan, E; Ibanoglu, C; Soydugan, F; Akan, MC; Demircan, OConsidering a sample of 20 eclipsing binary systems with delta Scuti type primaries, we discovered that there is a possible relation among the pulsation periods of the primaries and the orbital periods of the systems. According to this empirical relation, the longer the orbital period of a binary, the longer the pulsation period of its pulsating primary. Among the sample, the masses of the secondaries and the separations between the components are known for eight systems for which a log P-puls versus log F (the gravitational pull exerted per gram of the matter on the surface of the primaries by the secondaries) diagram also verifies such an interrelation between the periods. So, as the gravitational force applied by the secondary component onto the pulsating primary increases, its pulsation period decreases. The detailed physics underlying this empirical relation between the periods needs further confirmation, especially theoretically. However, one must also consider the fact that the present sample does not contain a sufficiently large sample of longer period (P > 5 d) binaries.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.
