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Öğe Quark and strange quark matter in f(R) gravity for Bianchi type I and V space-times(Springer/Plenum Publishers, 2012) Yılmaz, İhsan; Baysal, Hüsnü; Aktaş, CanBehaviors of quark matter and strange quark matter which exist in the first seconds of the early Universe in f(R) gravity are studied for Bianchi I and V universes. In this respect, we obtain exact solutions of the modified Einstein field equations by using anisotropy feature of Bianchi I and V space-times. In particular, we investigate exact f(R) functions for Bianchi I as the contribution of strange quark and quark matter. Also, we have concluded that quark matter may contribute to the early acceleration of the universe since quark matter behaves like phantom-type dark energy. Furthermore, obtained f(R) solutions represents early eras of the Universe since f(R) solutions for quark matter coincide with f(R) equations for inflation. From this point, we can reach the conclusion that quarks may be source of the early dark energy of the universe or source of little inflation due to their repulsive force.Öğe Non-existence of a massive scalar field for the Marder universe in Lyra and Riemannian geometries(Elsevier, 2012) Aygün, Sezgin; Aktaş, Can; Yılmaz, İhsanIn this paper, we have studied a massive scalar field for a Marder type universe in the context of Lyra and Riemannian geometries. From the exact solutions obtained we show that the massive scalar field does not survive in Lyra and Riemannian geometries for an anisotropic Marder type universe. Therefore we have solved the massless scalar field problem in Lyra and Riemann geometries for two cases. Also we have obtained vacuum solutions for homogeneous and anisotropic Marder space time in Lyra geometry and the solutions obtained are compared by considering Lyra and Riemann geometries. Finally, some physical and kinematical properties are discussed by using graphics. (C) 2011 Elsevier B.V. All rights reserved.Öğe Behaviors of dark energy and mesonic scalar field for anisotropic universe in f (R) gravity(Elsevier, 2012) Aktaş, Can; Aygün, Sezgin; Yılmaz, İhsanIn this Letter, we study behaviors of dark energy in the form of perfect fluid and mesonic scalar field for Marder space-time which is anisotropic and homogeneous in f (R) gravity. Exact solutions of the modified Einstein field equations in f (R) gravity are obtained by using anisotropic features, of Marder space-time. We do not make any assumptions about f (R) function while we are solving f (R I equations. We have investigated dark energy behaviors in f (R) gravity. We have concluded that dark energy in our model behaves like phantom type. Also we have concluded that mesonic scalar field transforms to another matters into time. In our solutions, obtained f (R) functions existed by dark energy and mesonic scalar field are same like general one accepted in the literature. Furthermore, physical and kinematical quantities are examined for two matters, separately. Finally obtained solutions are discussed. (C) 2011 Elsevier B.V. All rights reserved.Öğe Discovery of ? Sct components in eclipsing binary systems IQ CMa, AW men and W Vol(Oxford University Press, 2023) Ulaş, Burak; Ulusoy, CerenWe present the first evidence on the δ Sct type pulsations of the primary components of three eclipsing binaries IQ CMa, AW Men, and W Vol in the Transiting Exoplanet Survey Satellite (TESS) field. A comprehensive investigation of the binary properties is conducted. The light curves of the systems are analysed and the frequency analyses are performed to residual data. The systems are compared to the binaries of the same morphological types, and the primaries are examined in contrast to the δ Sct type pulsators. The results show that the systems are oscillating eclipsing Algol-type systems.Öğe Six Newly Discovered Eclipsing Binary Systems in the TESS field(Institute of Physics, 2023) Ulaş, Burak; Ayan, VildanWe present the first detailed investigation of six eclipsing binary systems in the TESS field. The TESS light curves of the targets are analyzed by determining the initial effective temperatures via SED fits. The absolute parameters are derived and the systems are compared to well-known binaries of the same type. Results show that CD-58791, CD-621257 and TYC 9356-355-1 are detached binary systems. CD-54942 and UCAC4 136-007295 are contact binaries while TYC 8508-1413-1 is a semidetached system.Öğe V355 And: a neglected detached binary in a multiple star system(Astronomical Institute, Slovak Academy of Sciences, 2021) Özkardeş, BurcuThe analysis of light curves (from TESS, ASAS-SN and KWS databases) of the eclipsing binary V355 And is presented for the first time. The O-C diagram was constructed using all available times of minimum light together with the ones determined in this study, and the revised ephemeris was obtained. The final photometric model describes V355 And as an Algollike type binary star with a detached configuration. Absolute parameters of the components of the system were found to be: masses, M1=1.56 ± 0.01 M⊙ and M2=1.38 ± 0.01 M⊙, radii, R1=1.70 ± 0.03 R⊙ and R2=1.38 ± 0.03 R⊙, and effective temperatures, T1=6650 ± 200 K and T2=6235 ± 201 K. Considering interstellar extinction the distance to V355 And was computed as 117 ± 7 pc. The evolutionary state of V355 And is also discussed using the Geneva stellar models.Öğe Photometric and period analysis of the eclipsing binary system V2783 Ori(Astronomical Institute, Slovak Academy of Sciences, 2021) Bulut, İbrahim; Bulut, AhmetIn this study we performed the first detailed photometric and period analysis of the recently discovered eclipsing binary star V2783 Ori. The analysis of the light curve has shown that the system is in a detached configuration, with the orbital eccentricity e = 0.274 ± 0.008. The photometric mass ratio of V2783 Ori determined from the light curve analysis is q= 0.734 ± 0.015. The absolute parameters of the system were obtained as a result of the light curve solution. Absolute parameters were found as follows: masses M1 = 1.80 ± 0.01 M⊙, M2 = 1.32 ± 0.01 M⊙, radii R1= 2.19 ± 0.10 R⊙, R2= 1.91 ± 0.10 R⊙, temperatures T1= 8325 ± 100 K and T2= 8300 ± 100 K. A comparison of these parameters with theoretical stellar models show that the secondary component is located inside the main-sequence band and still close to ZAMS, while the primary component is located in the middle of ZAMS-TAMS limits. The distance of the system determined from the absolute parameters, d= 1064 ± 150 pc, takes into account the interstellar reddening. The (O-C) diagram was discussed considering all reliable minima times found in the literature and new values for the parameters of the apsidal motion and light-time effect were found. The apsidal motion rate of V2783 Ori is co = 0.0063 ± 0.0017 deg cycle-, and it corresponds to an apsidal motion period of U= 656 ± 103 yr. The third body orbital period is 10 ± 2 yr, its minimal mass is 0.82 ± 0.11 M⊙.Öğe Catalog of W UMa type binary systems with additional components based on eclipsing time variations(Elsevier B.V., 2022) Bulut, İbrahim; Aşkın, GörkemA catalog of W UMa type eclipsing binary systems with tertiary components based on eclipse timing diagrams is presented listing the physical and orbital parameters (including third body parameters) of 150 W UMa type eclipsing binaries. In this study, the (O–C) diagrams of nine sample W UMa type eclipsing binary systems, based on the most reliable timings of minima in the literature, are analyzed to obtain the third-body parameters and significant statistical results are presented from the data in the catalog.Öğe New light curve analysis and period changes of the HW Vir-type binary system V1828 Aql(Elsevier B.V., 2022) Nehir, Çağlayan; Bulut, İbrahimThe new BVRI photometric observations of the HW Vir-type eclipsing binary system V1828 Aql (P = 0.11037399 days) were presented. From these measurements, 16 new eclipse times have been obtained. The light curves in BVRI colors and the radial curves were simultaneously analyzed by using the Wilson–Devinney method for the system parameters. The system consists of a very hot primary component (T1 = 42000 K) and a cold secondary component (T2 = 3077 ± 250 K). The absolute dimensions were found as follows: (M1 = 0.351 ± 4 0.040 M⊙, M2 = 0.095 ± 0.011 M⊙, R1 = 0.176 ± 0.007 R⊙, R2 = 0.140 ± 0.007 R⊙, L1 =86.91 ± 6.76 L⊙ and L2 = 0.002 ± 0.001 L⊙). The orbital period variation of V1828 Aql was made using all available light minimum times. From the (O - C) diagram, the orbital period shows a variation possibly attributable to the light travel time effect by the presence of the third body. The third body orbital period is P3 = 3317.7−17.2+18.9 days, its minimal mass is M3 = 13.24−0.14+0.13 Mj. The mass value calculated for the third body shows, that this object is right at the border between the planets and the brown dwarfs.Öğe Four New Eclipsing Binary Systems in the TESS field: CD-34 13220, HD 295082, TYC 6484-426-1 and TYC 6527-2310-1(IOP Publishing, 2021) Ulaş, BurakWe present the first evidence for the binarity of four targets in the TESS field. The temperatures are estimated by SED analysis and the orbital periods are determined. The TESS light curves of the systems are analyzed and the orbital and the absolute parameters are derived. The targets are also compared to wellstudied binary systems with the same morphological type and their evolutionary states are discussed. Our results indicate that the stars belong to the class of eclipsing detached binary systems.Öğe Absolute parameters of young stars: PU Pup(IOP Publishing, 2021) Erdem, Ahmet; Sürgit, Derya; Banks, Timothy S.; Özkardeş, Burcu; Budding, EdwinWe present combined photometric and spectroscopic analyses of the southern binary star PU Pup. High-resolution spectra of this system were taken at the University of Canterbury Mt. John Observatory in the years 2008 and again in 2014-15. We find the light contribution of the secondary component to be only ∼2% of the total light of the system in optical wavelengths, resulting in a single-lined spectroscopic binary. Recent TESS data revealed grazing eclipses within the light minima, though the tidal distortion, examined also from HIPPARCOS data, remains the predominating light curve effect. Our model shows PU Pup to have the more massive primary relatively close to filling its Roche lobe. PU Pup is thus approaching the rare ‘fast phase’ of interactive (Case B) evolution. Our adopted absolute parameters are as follows: M1 = 4.10 (±0.20) M , M2 = 0.65 (±0.05) M , R1 = 6.60 (±0.30) R , R2 = 0.90 (±0.10) R ; T1 = 11500 (±500) K, T2 = 5000 (±350) K; photometric distance = 186 (±20) pc, age = 170 (±20) My. The less-massive secondary component is found to be significantly oversized and overluminous compared to standard Main Sequence models. We discuss this discrepancy referring to heating from the reflection effect.
