Yazar "Dogru, S. S." seçeneğine göre listele
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Öğe First period analyses of five neglected Algol-type eclipsing binaries(Elsevier Science Bv, 2007) Erdem, A.; Soydugan, Faruk; Dogru, S. S.; Oezkardes, B.; Dogru, D.; Tueysuez, A.; Demircan, O.We present the first study of the orbital period variations of five neglected Algol-type eclipsing binaries TT And, V342 Aql, RW Cap, Z Cas and TW Lac, using their O-C diagrams gathered from all available times of eclipse minima. These O-C diagrams indicate that term periodic variations superimposed on secular period increases as expected in mass transferring Algols. However, due to short me coverage of the data, the secular period increase is not clear in the case of BZ Cas and V342 Aql. The secular period increase is.terpreted in terms of the combined effect of mass transfer between the components of the system and the mass loss by a stellar wind on the system. The mass transfer rates from the less massive secondary components to the more massive primaries for non-conservave cases would be about 10(-7) M-circle dot/yr and 10(-8)M(circle dot))/y for RW Cap and V342 Aql, respectively, and 10(-9)M(circle dot)/yr for TT And and TW . Therefore, the Algol systems RW Cap and V342 AqI have the largest mass transfer rate, which could be in Case AB type, while tose of the Algol systems TT And and TW ' Lac display the slow mass transfer rate and they could be in Case B type. The sinusoidal -rms of the orbital period variations of all five Algol systems can be due to either by the light-time effects due to unseen components in iese systems, or by the cyclic magnetic activity effects of the cool secondary components. The possible third bodies in all five Algol binaes would have masses larger than one solar mass. If these hypothetical large massive third bodies were normal stars, they should be Aectable. Therefore, new photometric and spectroscopic observations of these systems and careful analyses of those data are required. otherwise, the cyclic magnetic activity effects of the secondary components could be the basis of a working hypothesis in explaining the,clic period variations of these systems. 2007 Elsevier B.V. All rights reserved.Öğe Orbital period variations of four Algol-type eclipsing binaries: SW Cyg, UU Leo, XX Cep and BO Vul(Wiley-V C H Verlag Gmbh, 2007) Erdem, A.; Dogru, S. S.; Bakis, V.; Demircan, O.The orbital period behaviours of four Algol-type eclipsing binaries SW Cyg, UU Leo, XX Cep and BO Vul are studied, by using all available times of minimum light in the literature. Their O-C diagrams were represented by long-period sinusoidal variations superimposed on parabolic forms. The parabolic forms for SW Cyg and UU Leo correspond to secular period increases, while for XX Cep and 130 Vul to secular period decreases. To explain these observed secular changes in these four Algol systems, we considered the combined effect of the mass transfer from the less massive component to the more massive one and the mass loss from the system. We concluded that the dominant mechanism for observed long-term period change of SW Cyg and UU Leo is the mass transfer, and that of XX Cep and BO Vul is the mass loss from the systems. It is interesting that the mass transfer rates (i.e., 10-(7)-10(-8) M-circle dot/yr) found for all four Algol binaries are at the upper limit of those generally accepted for Algols. However, assuming the mass loss via circumbinary disks of Chen et al. (2006) reduces the rate to 10(-8)-10(-9) M-circle dot/yr. We interpreted the tilted sinusoidal variations in all cases in terms of the light-time effect due to unseen components in the systems. Unacceptably large hypothetical third body masses in the case of SW Cyg and UU Leo, and common nature of the cyclic O-C variations in semi-detached Algols recall the cyclic magnetic activity effects of the secondary components as the working hypothesis in explaining cyclic period variations of these systems. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.Öğe Period studies of classical Algol-type binaries II: UX Leo, RW Mon, EQ Ori, XZ UMa and AX Vul(Elsevier Science Bv, 2011) Soydugan, Faruk; Erdem, A.; Dogru, S. S.; Alicavus, F.; Soydugan, Esin; Cicek, C.; Demircan, O.This study presents an investigation of the orbital period variations of five Algol type binaries, UX Leo, RW Mon, EQ Ori, XZ UMa and AX Vul based on all available minima times. The O-C diagrams of all systems exhibit a periodic variation superimposed on a downward parabolic segment. The mass loss due to magnetic braking effect in the cooler components is assumed to account for the parabolic variation with a downward shape, while it is suggested that the light-time effect (LITE) due to an unseen component around the eclipsing binaries explains the tilted sinusoidal changes in their O-C diagrams. The orbital period decrease rates for the systems are estimated as approximately between about 0.7 and 2.5 s per century. It is clearly seen that mass loss effect is more dominant than the expected mass transfer for classical Algols in this study. The minimum mass of the probable third bodies around the eclipsing pairs was calculated to be <= 0.5 M-circle dot, except for UX Leo, in which it was estimated to be approximately 0.9 M-circle dot. In order to search for third lights in the light curves of five systems, the V-light curves of the systems were analyzed and their physical and photometric parameters were determined. For UX Leo, a significant third light contribution was determined. We found a very small third light that can be tested using multi-color light curves, for RW Mon, EQ On and XZ UMa, while a third light for AX Vul could not be exposed. (C) 2010 Elsevier B.V. All rights reserved.Öğe Period studies of five neglected Algol-type binaries: RW Cet, BO Gem, DG Lac, SW Oph and WY Per(Elsevier Science Bv, 2010) Erdem, A.; Dogru, S. S.; Soydugan, Faruk; Cicek, C.; Demircan, O.We investigated the orbital period variations of five neglected Algol-type eclipsing binaries (RW Cet, BO Gem, DG Lac, SW Oph and WY Per) in this study Their O-C diagrams display tilted sinusoidal variations superimposed on upward parabolic forms The parabolic variations, which correspond to secular period increases, were interpreted in terms of the combined effect of mass transfer and loss Then, the mass transfer rates from the less massive secondary components to more massive primaries for non-conservative cases were calculated to be similar to 10(-7) M(circle dot)/yr for RW Cet. DG Lac and SW Oph and similar to 10(8) M(circle dot)/yr for BO Gem and WY Per The tilted (eccentric) sinusoidal representations of the O-C variations were interpreted in terms of the light-time effect due to unseen components in the systems. The possible third bodies in four Algol binaries (excluding RW Cet) would have masses larger than one solar mass If these hypothetical large massive third bodies were normal stars, they should be detectable Therefore, new astrometric, photometric and spectroscopic observations of these systems and careful analyses of the resulting data are required (C) 2010 Elsevier B V All rights reservedÖğe Photometry of three chromospherically active stars: V340 Gem, SAO 62042 and FI Cnc(Elsevier, 2009) Erdem, A.; Budding, E.; Soydugan, Esin; Soydugan, Faruk; Dogru, S. S.; Dogru, D.; Tuysuz, M.We present a photometric study of three chromospherically active stars with long periods (V340 Gem, SAO 62042 and FI Cnc). The observations were made at the COMU Observatory in 2006 and 2007. We have made initial photometric analyses of V340 Gem and SAO 62042, which are newly discovered RS CVn-type SB1 binaries, and established the photometric variations of FI Cnc, which is a single G8III active star. Photometric rotation periods of these stars were obtained by analyzing their light variations. The light variations, observed over three or more consecutive orbital cycles, were investigated by using spot models with the program SPOT. We also discussed the surface differential rotation coefficient for the primary component of the SB1 binary star SAO 62042 in this study, using our own photometric period together with an orbital period taken from the literature. (C) 2008 Elsevier B.V. All rights reserved.Öğe The 2006/2007 photometric activity of three chromospherically active stars: V2075 Cyg, FG UMa and BM CVn(Elsevier Science Bv, 2009) Erdem, A.; Budding, E.; Soydugan, Esin; Bakis, H.; Dogru, D.; Dogru, S. S.; Tuysuz, M.We present new multiband CCD photometric observations of three chromospherically active stars with long periods (V2075 Cyg, FG UMa and BM CVn). The observations were made at the Canakkale Onsekiz Mart University Observatory in 2006 and 2007. We analyzed BVRI (Bessell) CCD observations of these three RS CVn-type SB1 binaries with the following three steps: (i) Photometric rotation periods were obtained by analyzing their light variations with a differential corrections method and a Fourier transform technique. (ii) Light variations. observed over three or more consecutive orbital cycles, were investigated by using dark (cool) spot models with the program SPOT. (iii) Surface differential rotation coefficients for the primary components of these binaries were derived using our own photometric periods together with orbital periods taken from the literature. (C) 2009 Elsevier B.V. All rights reserved.Öğe The CCD photometric study of the newly identified RS CVn binary star V1034 Hercules(Elsevier Science Bv, 2009) Dogru, D.; Erdem, A.; Dogru, S. S.This paper presents a new CCD Bessell VRcIc light curves and photometric analysis of the newly discovered RS CVn type eclipsing binary star VI 034 Her. The light curves were obtained at the Canakkale Onsekiz Mart University Observatory in 2006. Variations of the orbital period of the system were firstly studied. The (O - C) diagram with a low range of observing time of about 20 years shows an upward parabola, which indicates a secular increase in the orbital period of the system. The light curves are generally those of detached eclipsing binaries; however, there are large asymmetries between maxima. The VRcIc light curves were analysed with two different fitting procedures: Wilson-Devinney method supplemented with a Monte Carlo type algorithm and Information Limit Optimization Technique (ILOT). Our general results find V1034 Her. as a well detached system, in which the components are filling similar to 65% of their Roche lobes. Light curve asymmetries of the system are explained in terms of large dark starspots on the primary component. The primary star shows a long-lived spot distribution with active longitudes in the same hemisphere. (C) 2009 Elsevier B.V. All rights reserved.Öğe The chromospherically active binary CF Tuc revisited(Oxford Univ Press, 2009) Dogru, D.; Erdem, A.; Dogru, S. S.; Zola, S.This paper presents results derived from analysis of new spectroscopic and photometric observations of the chromospherically active binary system CF Tuc. New high-resolution spectra, taken at the Mt. John University Observatory in 2007, were analysed using two methods: cross-correlation and Fourier-based disentangling. As a result, new radial velocity curves of both components were obtained. The resulting orbital elements of CF Tuc are a(1) sin i = 0.0254 +/- 0.0001 au, a(2) sin i = 0.0228 +/- 0.0001 au, M-1 sin i = 0.902 +/- 0.005 M-circle dot and M-2 sin i = 1.008 +/- 0.006 M-circle dot. The cooler component of the system shows H alpha and Ca ii H&K emissions. Using simultaneous spectroscopic and photometric observations, an anticorrelation between the H alpha emission and the BV light curve maculation effects was found. This behaviour indicates a close spatial association between photospheric and chromospheric active regions. Our spectroscopic data and recent BV light curves were solved simultaneously using the Wilson-Devinney code. A dark spot on the surface of the cooler component was assumed to explain large asymmetries observed in the light curves. The following absolute parameters of the components were determined: M-1 = 1.11 +/- 0.01 M-circle dot, M-2 = 1.23 +/- 0.01 M-circle dot, R-1 = 1.63 +/- 0.02 R-circle dot, R-2 = 3.60 +/- 0.02 R-circle dot, L-1 = 3.32 +/- 0.51 L-circle dot and L-2 = 3.91 +/- 0.84 L-circle dot. The primary component has an age of about 5 Gyr and is approaching its main-sequence terminal age. The distance to CF Tuc was calculated to be 89 +/- 6 pc from the dynamic parallax, neglecting interstellar absorption, in agreement with the Hipparcos value. The orbital period of the system was studied using the O-C analysis. The O-C diagram could be interpreted in terms of either two abrupt changes or a quasi-sinusoidal form superimposed on a downward parabola. These variations are discussed by reference to the combined effect of mass transfer and mass loss, the Applegate mechanism and also a light-time effect due to the existence of a third body in the system.Öğe The detached eclipsing binary TX Her revisited(Elsevier, 2011) Erdem, A.; Alicavus, F.; Soydugan, Faruk; Dogru, S. S.; Soydugan, Esin; Cicek, C.; Demircan, O.This paper presents new CCD Bessell BVRI light curves and photometric analysis of the Algol-type binary star TX Her. The CCD observations were carried out at Canakkale Onsekiz Mart University Observatory in 2010. New BVRI light curves from this study and radial velocity curves from Popper (1970) were solved simultaneously using modern light and radial velocity curves synthesis methods. The general results show that TX Her is a well-detached eclipsing binary, however, both component stars fill at least half of their Roche lobes. A significant third light contribution to the total light of the system could not be determined. Using O-C residuals formed by the updated minima times, an orbital period study of the system was performed. It was confirmed that the tilted sinusoidal O-C variation corresponds to an apparent period variation caused by the light travel time effect due to an unseen third body. The following absolute parameters of the components were derived: M-1 = 1.62 +/- 0.04 M-circle dot, M-2 = 1.45 +/- 0.03 M-circle dot, R-1 = 1.69 +/- 0.03 R-circle dot, R-2 = 1.43 +/- 0.03 R-circle dot, L-1 = 8.21 +/- 0.90 L-circle dot, and L-2 = 3.64 +/- 0.60 L-circle dot. The distance to TX Her was calculated as 155 +/- 10 pc, taking into account interstellar extinction. The position of the components of TX Her in the HR diagram are also discussed. The components are young stars with an age of similar to 500 Myr. (C) 2011 Elsevier B.V. All rights reserved.
