Yazar "Dogru, D." seçeneğine göre listele

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    A catalogue of chromospherically active binary stars (third edition)
    (Wiley-Blackwell, 2008) Eker, Z.; Ak, N. Filiz; Bilir, S.; Dogru, D.; Tueysuez, M.; Soydugan, Esin; Bakis, H.
    The catalogue of chromospherically active binaries (CABs) has been revised and updated. With 203 new identifications, the number of CAB stars is increased to 409. The catalogue is available in electronic format where each system has a number of lines (suborders) with a unique order number. The columns contain data of limited numbers of selected cross references, comments to explain peculiarities and the position of the binarity in case it belongs to a multiple system, classical identifications (RS Canum Venaticorum, BY Draconis), brightness and colours, photometric and spectroscopic data, a description of emission features (Ca II H and K, H alpha, ultraviolet, infrared), X-ray luminosity, radio flux, physical quantities and orbital information, where each basic entry is referenced so users can go to the original sources.
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    Cool Active Binaries Recently Studied in the CAAM Stellar Program
    (Astronomical Soc Pacific, 2010) Cicek, C.; Erdem, A.; Soydugan, Faruk; Dogru, D.; Ozkardes, B.; Erkan, N.; Budding, E.
    We summarize recent work on cool active stars in our programme. We carried out photometry at the canakkale Onsekiz Mart University (COMU) observatory, and high-resolution spectroscopy at Mt John University Observatory, as well as collecting data from other facilties. A combination of analysis methods, including our information limit optimization technique (ILOT) with physically realistic fitting functions, as well as other public-domain software packages, have been used to find reliable parameters. Stars in our recent programme include V1430 Aql, VI 034 Her, V340 Gem, SAO 62042, FI Cnc, V2075 Cyg, FG UMa and BM CVn. Light variations, sometimes over numerous consecutive cycles, were analysed. For AB Dor and CF Tuc, we compared broadband (B and V) maculation effects with emission features in the Ca II K and H-alpha lines. Broadband light curves typically show one or two outstanding maculae. These appear correlated with the main chromospheric activity sites ('faculae'), that occur at similar latitudes and with comparable size to the photometric umbrae, but sometimes with significant displacements in longitude. The possibility of large-scale bipolar surface structure is considered, keeping in mind solar analogies. Such optical work forms part of broader multiwavelength studies, involving X-ray and microwave observations, also mentioned.
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    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.
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    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.
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    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.
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    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.
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    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.