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Öğe A Comprehensive Study of the Eclipsing Binaries V1241 Tau and GQ Dra(Copernicus Foundation Polish Astronomy, 2020) Ulas, B.; Gazeas, K.; Liakos, A.; Ulusoy, C.; Stateva, I; Erkan, N.; Napetova, M.We present new photometric and spectroscopic observations and analyses for the eclipsing binary systems V1241 Tau and GQ Dra. Our photometric light and radial velocity curve analyses combined with the TESS light curves show that both are conventional semi-detached binary systems. Their absolute parameters are also derived. We present the O-C analyses of the systems and we propose the most likely orbital period modulating mechanisms. Furthermore, Fourier analyses are applied to the photometric residual data of the systems to check for the pulsational behavior of the components. We conclude that the primary component of the system GQ Dra is a delta Set type pulsator with a dominant pulsation frequency of 18.58 d(-1) based on our B filter residual light curve although it cannot be verified by 30-minute cadence TESS data. No satisfactory evidence of pulsational behavior for V1241 Tau was verified. Finally, the evolutionary tracks of the components of both systems are calculated. Their locations within evolutionary diagrams are compared with other Algol-type systems.Öğe A study of variability of the marginal Am star HD 176843 observed in the Kepler field(Elsevier Science Bv, 2019) Ulusoy, C.; Stateva, I.; Ulas, B.; Alicavus, F.; Iliev, I. Kh.; Napetova, M.; Kaygan, E.We present results of a study of variability of the marginal Am star HD 176843 observed in the Kepler field. Kepler photometry and ground-based spectroscopy are used to investigate the light variations of the star. HD 176843 is classified as a marginal Am star that shows delta Sct type pulsations. From an analysis of the Kepler time series, we find that the light curve of HD 176843 is dominated by three modes with frequencies f(1) = 0.1145, f(2) = 0.0162 and ,f(3) = 0.1078 d(-1). The amplitude of the radial velocity variations of about 10 km/s is much more than the radial velocity errors and allows us to conclude clear radial velocity variations. Using the radial velocity data and the adopted spectra, the orbital solution of HD 176843 is also obtained with an orbital period of 34.14 days. However, the available photometric data show no significant evidence for any possible motion in the binary system.Öğe Absolute properties of the binary system BB Pegasi(Univ Chicago Press, 2007) Kalomeni, B.; Yakut, K.; Keskin, V.; Degirmenci, O. L.; Ulas, B.; Kose, O.We present ground-based photometry of the low-temperature contact binary BB Peg. We collected all the times of mid-eclipse available in the literature and combined them with those obtained in this study. Analyses of the data indicate a period increase of (3.0 +/- 0.1) x 10(-8) days yr 1. This period increase of BB Peg can be interpreted in terms of the mass transfer 2.4 x 10(-8) Mo yr(-1) from the less massive to the more massive component. The physical parameters have been determined as M-c, = 1.42 Mo, My, = 0.53 Mo, R-c, = 1.29 Ro, Rh = 0.83 R-circle dot, L-c, = 1.86 L-c, and L-h = 0.94 L-circle dot through simultaneous solutions of light and of the radial velocity curves. The orbital parameters of the third body, which orbits the contact system in an eccentric orbit, were obtained from the period variation analysis. The system is compared to the similar binaries in the Hertzsprung-Russell and mass-radius diagrams.Öğe Numerical solutions of the equation concerning small adiabatic oscillations of pulsating components in double star systems(Wiley-V C H Verlag Gmbh, 2012) Ulas, B.The equation governing small adiabatic radial oscillations for pulsating components in close binary stars modelled by tidally and rotationally distorted Roche geometry is solved numerically. With assumed initial conditions, solutions for systems with different mass ratios are presented. The changes in relative wave amplitude with various parameters are shown. The variation of the ratio of the pulsation frequencies of distorted to undistorted stars for given mass ratio of the binary systems is also investigated. Observational evidence is examined by using two data sets that show the modelled effects, by taking into account likely practical factors. The results show that the measured frequencies and amplitudes of surface waves can vary slightly for distorted stars in comparison to undistorted ones ((c) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)Öğe The Algol-type eclipsing binaries RW CrB and VZ Leo: new RI photometric study and search for pulsations(Springer, 2009) Ulas, B.; Niarchos, P. G.; Lampens, P.; Liakos, A.In this study we present the new R and I light curve solutions for the eclipsing binary systems RW CrB and VZ Leo, which for VZ Leo is the first one in the literature. Our new observations have been analyzed using the Wilson-Devinney code from which new geometric and photometric elements are derived. The geometry of both stars is that of a semi-detached binary system where the secondary component fills its Roche lobe while the primary component is well inside. In the case of RW CrB, asymmetry in the light curve was explained by a spot model. The orbital period changes of both systems were studied and the results indicated a period decrease which can be explained by angular momentum loss. We also investigated the possibility of pulsations of the primary components since these systems are mentioned as candidates of delta Sct type pulsation. However, a time-series analysis of the residual curves in the filter I does not indicate any evidence of periodic light variation for both systems. Finally, we compared the results obtained for both binary stars to those of similar systems.Öğe The low mass ratio contact binary system V728 Herculis(Elsevier Science Bv, 2016) Erkan, N.; Ulas, B.We present the orbital period study and the photometric analysis of the contact binary system V728 Her. Our orbital period analysis shows that the period of the system increases (dP/dt = 1.92 x 10(-7)dyr(-1)) and the mass transfer rate from the less massive component to more massive one is 2.51 x 10(-8) M(circle dot)y(-1). In addition, an advanced sinusoidal variation in period can be attributed to the light-time effect by a tertiary component or the Applegate mechanism triggered by the secondary component. The simultaneous multicolor BVR light and radial velocity curves solution indicates that the physical parameters of the system are M-1 = 1.8M(circle dot), M-2 = 0.28M(circle dot), R-1 = 1.87R(circle dot), R-2 = 0.82R(circle dot), L-1 = 5.9L(circle dot), and L-2 = 1.2L(circle dot). We discuss the evolutionary status and conclude that V728 Her is a deep (f = 81%), low mass ratio (q = 0.16) contact binary system. (C) 2015 Elsevier B.V. All rights reserved.
