Astrofizik Araştırma Merkezi ve Ulupınar Gözlemevi Yayın Koleksiyonu

Bu koleksiyon için kalıcı URI

https://hdl.handle.net/20.500.12428/3697

Listeleniyor 1 - 10 / 10

Behaviors of dark energy and mesonic scalar field for anisotropic universe in f (R) gravity
(Elsevier, 2012) Aktaş, Can; Aygün, Sezgin; Yılmaz, İhsan
In 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.
Single-lined eclipsing binaries with ? Scuti components: GQ Dra, RR Lep, and TYC 683-640-1
(Oxford University Press, 2024) Kahraman Aliçavuş, Filiz; Aliçavuş, Fahri; Çoban, Çağlar Gani; Handler, G.; De Cat, P.
Eclipsing binaries with (a) pulsating component(s) are remarkable objects to investigate the evolution and structure of stellar systems. Detailed studies of such systems are also important to reveal their pulsation properties. The largest sample of pulsating eclipsing binaries is the one containing δ Scuti variables. In this study, we present a comprehensive spectroscopic and photometric study of three such systems, GQ Dra, RR Lep, and TYC 683-640-1. Their orbital parameters were derived from their large-amplitude radial velocity variations. All systems were found to be single-lined eclipsing binaries. We determined the atmospheric parameters of the primary components, which are the more luminous ones. By using the results of the spectroscopic analysis, the binarity of the systems was modelled and the fundamental stellar parameters (mass, radius) of each system were obtained. In addition, the pulsations of the systems were analysed. Both GQ Dra and RR Lep exhibit frequencies that are modulated with the orbital period. Therefore, the pulsating components of these systems are identified as candidate tidally tilted pulsators.
First Detailed Photometric Investigation on the Nature of Contact Binary System AA Cet
(Institute of Physics, 2023) Yıldırım, Muhammed Faruk
The TESS light curve (LC) of the marginal contact binary AA Cet was analyzed simultaneously with the radial velocity and the orbital period (OP) change of the system was investigated. The physical parameters of the system were obtained by analyzing the LC of AA Cet with the Wilson-Devinney method, and the absolute parameters of the components were calculated using the results obtained. For the components of AA Cet, the masses and radii were calculated as M 1 = 1.39 ± 0.04 M ⊙, M 2 = 0.48 ± 0.02 M ⊙ and R 1 = 1.64 ± 0.03 R ⊙, R 2 = 1.01 ± 0.04 R ⊙, respectively. AA Cet is a marginal contact binary with a temperature difference of 1305 K between its components. A total of 14 eclipse times were obtained from the TESS data and used in the OP analysis together with those collected from the literature. It has been observed that the change in the OP of AA Cet is in the form of a decreasing parabola. Conservative mass transfer between the components has been interpreted as the reason for this change. The OP decrease amount of AA Cet was obtained as dP/dt = 0.0062 ± 0.0006 s yr−1, and the reason for this decrease was attributed to a 3.3(9) × 10−8 M ⊙ mass transfer per year from the more massive component to the less massive one. The age of AA Cet has been estimated as 7 Gyr, as the age of contact systems helps us to understand their evolution.
Comprehensive spectroscopic and photometric study of pulsating eclipsing binary star AI Hya
(Oxford University Press, 2023) Kahraman Alicavuş, Filiz; Aliçavuş, Fahri; Pawar, T.; Helminiak, K. G.; Handler, G.; Moharana, A.
The pulsating eclipsing binaries are remarkable systems that provide an opportunity to probe the stellar interior and to determine the fundamental stellar parameters precisely. Especially the detached eclipsing binary systems with (a) pulsating component(s) are significant objects to understand the nature of the oscillations since the binary effects in these systems are negligible. Recent studies based on space data have shown that the pulsation mechanisms of some oscillating stars are not completely understood. Hence, comprehensive studies of a number of pulsating stars within detached eclipsing binaries are important. In this study, we present a detailed analysis of the pulsating detached eclipsing binary system AI Hya which was studied by two independent groups with different methods. We carried out a spectroscopic survey to estimate the orbital parameters via radial velocity measurements and the atmospheric parameters of each binary component using the composite and/or disentangled spectra. We found that the more luminous component of the system is a massive, cool and chemically normal star while the hotter binary component is a slightly metal-rich object. The fundamental parameters of AI Hya were determined by the analysis of binary variations and subsequently used in the evolutionary modelling. Consequently, we obtained the age of the system as 850 ± 20 Myr and found that both binary components are situated in the δ Scuti instability strip. The frequency analysis revealed pulsation frequencies between 5.5 and 13.0 d−1 and we tried to estimate which binary component is the pulsating one. However, it turned out that those frequencies could originate from both binary components.
First photometric study of three eclipsing binary star systems: V495 Aur, V589 Aur and V478 Cam
(Elsevier B.V., 2023) Öztürk, Oğuz; Erdem, Ahmet
The light curve solutions and orbital period analysis of V495 Aur, V589 Aur and V478 Cam eclipsing binary star systems are presented for the first time in this study. Transiting Exoplanet Survey Satellite (TESS) observations were used as observational data. From the light curve solutions, it was concluded that all three systems are semi-detached binary star systems in which the secondary components fill their Roche lobes. The absolute parameters of the systems were also estimated. Accordingly, the photometric mass ratios of V495 Aur, V589 Aur and V478 Cam are found to be 0.251±0.035, 0.254±0.038 and 0.078±0.010, respectively. Upward parabolic change was observed in the O-C diagrams of all the systems considered. As a result of parabolic changes, we concluded that the orbital periods of the V495 Aur, V589 Aur and V478 Cam systems increased secularly with a rate of 0.050±0.010 s/year, 0.018±0.004 s/year and 0.070±0.015 s/year, respectively. The increases in orbital periods are explained by the dominant mass transfer mechanism from the secondary components to the primary components. In addition, the mass transfer rates between components and the rates of mass lost from the systems were estimated.
Semi-detached Algol type binaries with increasing orbital periods: Case studies of BD Vir, BO Gem, DG Lac, RW Cet, and RX Hya
(Elsevier B.V., 2023) Yıldırım, Muhammed Faruk; Soydugan, Faruk
This paper presents results from photometric investigations of five semi-detached binaries. Using the TESS and KEPLER (K2) databases, light curves of classical Algol systems BD Vir, BO Gem, DG Lac, RW Cet, and RX Hya were performed in detail. As a result of light curve analysis, the basic astrophysical parameters of the systems were estimated. The masses and radii of the primary components were estimated as 1.95(20) M⊙, 2.22(22) M⊙, 1.95(20) M⊙, 1.95(20) M⊙, 1.75(18) M⊙ and 2.29(3) R⊙, 2.21(2) R⊙, 2.09(1) R⊙, 1.86(2) R⊙, 1.79(3) R⊙ for BD Vir, BO Gem, DG Lac, RW Cet, and RX Hya, respectively. Likewise, the masses and radii of the secondary components were estimated as 0.45(4) M⊙, 0.47(4) M⊙, 0.26(2) M⊙, 0.50(5) M⊙, 0.47(2) M⊙ and 2.94(3) R⊙, 3.90(2) R⊙, 2.17(1) R⊙, 1.35(2) R⊙, 2.57(4) R⊙ for BD Vir, BO Gem, DG Lac, RW Cet, and RX Hya, respectively. It was determined that the orbital periods of the BD Vir, BO Gem, DG Lac, RW Cet, and RX Hya increased with rates of 8.4(3), 24.2(8), 8.1(3), 1.3(1) and 12.5(6) s century−1, respectively. In addition, sinusoidal changes were determined in the orbital period analysis and it was discussed that these sinusoidal changes could be caused by possible component(s) or magnetic activity around the binary. The positions of the components of BD Vir, BO Gem, DG Lac, RW Cet, and RX Hya in logTeff−logL and logM−logR diagrams are discussed.
Cylindrically symmetric unimodular f(R) black holes
(World Scientific Publishing, 2021) Aydın, Hüseyin; Doğru, Melis Ulu
In this paper, we examine massless scalar field by using unimodular f(R) theory. It is taken into account unimodular and cylindrically symmetric spacetime which provides convenience in researching black hole. The field equations in unimodular f(R) theory for given spacetime with massless scalar field and additional Bianchi identities are solved. Cylindrically symmetric anti-de Sitter (AdS)-Schwarzschild-like and AdS-Reissner-Nordstrom-like black hole spacetimes are achieved. Equations of motion are derived by using Hamiltonian. Orbits of massless test particles are depicted. Obtained line element asymptotically converges to dS/AdS spacetime. Weak and strong energy conditions of the massless scalar field are obtained with Raychaudhuri equations in unimodular f(R) theory. Also, stiff fluid interpretation of scalar field is reviewed.
The First Light Curve Solutions and Period Study of BQ Ari
(Springer, 2021) Poro, A.; Davoudi, F.; Kahraman Aliçavuş, Filiz; Khakpash, S.; Esmer, E. M.; Baştürk, O.
The first analysis of the photometric observation in BVR filters of a W UMa type binary system BQ Ari was performed. Light curve analysis was performed using Wilson-Devinney (W-D) code combined with a Monte Carlo (MC) simulation to determine its photometric and geometric elements and their uncertainties. These results show that BQ Ari is a contact binary system with a photometric mass ratio q = 0.548 +/- 0.019, a fillout factor f = 24 +/- 0.8%, and an orbital inclination of i = 85.09 +/- 0.45. We used the parallax from Gaia EDR3 for calculating the absolute parameters of the binary system. This study suggested a new linear ephemeris for BQ Ari, combining our new mid-eclipse times and the previous observations, which we analyzed using the Monte Carlo Markov Chain (MCMC) method. We present the first analysis of the system's orbital period behavior by analyzing the O - C diagram using the Genetic Algorithm (GA) and the MCMC approaches in OCFit code. We attempted to explain the analysis of the residuals of linear fit in the O - C diagram with two approaches; "LiTE + Quadratic" and "Magnetic activity + Quadratic." Although we consider the magnetic activity to be probable, the system should be studied further in order to reveal the nature of orbital period variations.
Optimization applied to selected exoplanets
(Springer, 2021) Ng, Shi Yuan; Jiadi, Zhou; Püsküllü, Çağlar; Banks, Timothy; Budding, Edwin; Rhodes, Michael D.
Transit and radial velocity models were applied to archival data in order to examine exoplanet properties, in particular for the recently discovered super-Earth GJ357b. There is however considerable variation in estimated model parameters across the literature, and especially their uncertainty estimates. This applies even for relatively uncomplicated systems and basic parameters. Some published accuracy values thus appear highly overoptimistic. We present our reanalyses with these variations in mind and specify parameters with appropriate confidence intervals for the exoplanets Kepler-1b, -2b, -8b, -12b, -13b, -14b, -15b, -40b and -77b and 51 Peg. More sophisticated models in WINFITTER (WF), EXOFAST and DACE were applied, leading to mean planet densities for Kepler-12b, -14b, -15b and -40b as: 0:11 0:01, 4:04 0:58, 0:43 0:05 and 1:19þ0:31 0:36 g per cc respectively. We confirm a rocky mean density for the Earth-like GJ357b, although we urge caution about the modelling given the low S/N data. We cannot confidently specify parameters for the other two proposed planets in this system.
Physical parameters of close binary systems: VIII
(Royal Astronomical Society, 2021) Gazeas, K.; Zola, S.; Liakos, A.; Zakrzewski, B.; Rucinski, S. M.; Kreiner, J. M.; Ogloza, W.; Drozdz, M.; Koziel-Wierzbowska, D.; Stachowski, G.; Siwak, M.; Baran, A.; Kjurkchieva, D.; Marchev, D.; Erdem, A.; Szalankiewicz, S.
This paper presents the results of a combined spectroscopic and photometric study of 20 contact binary systems: HV Aqr, OO Aql, FI Boo, TX Cnc, OT Cnc, EE Cet, RW Com, KR Com, V401 Cyg, V345 Gem, AK Her, V502 Oph, V566 Oph, V2612 Oph, V1363 Ori, V351 Peg, V357 Peg, Y Sex, V1123 Tau, and W UMa, which was conducted in the frame of the W UMa Project. Together with 51 already covered by the project and an additional 67 in the existing literature, these systems bring the total number of contact binaries with known combined spectroscopic and photometric solutions to 138. It was found that mass, radius, and luminosity of the components follow certain relations along the MS and new empirical power relations are extracted. We found that 30 per cent of the systems in the current sample show extreme values in their parameters, expressed in their mass ratio or fill-out factor. This study shows that, among the contact binary systems studied, some have an extremely low mass ratio (q < 0.1) or an ultrashort orbital period (P-orb < 0.25 d), which are expected to show evidence of mass transfer progress. The evolutionary status of these components is discussed with the aid of correlation diagrams and their physical and orbital parameters compared to those in the entire sample of known contact binaries. The existence of very short orbital periods confirms the very slow nature of the merging process, which seems to explain why their components still exist as MS stars in contact configurations even after several Gyr of evolution.

Güncel Gönderiler