Astrofizik Araştırma Merkezi ve Ulupınar GözlemeviAstrophysics Research Center (ÇARC) and Ulupınar Observatory (UPO)https://hdl.handle.net/20.500.12428/36962023-02-08T06:52:06Z2023-02-08T06:52:06ZCylindrically symmetric unimodular f(R) black holesAydın, HüseyinDoğru, Melis Uluhttps://hdl.handle.net/20.500.12428/37672022-12-31T09:47:41Z2021-01-01T00:00:00ZCylindrically symmetric unimodular f(R) black holes
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.
2021-01-01T00:00:00ZThe First Light Curve Solutions and Period Study of BQ AriPoro, A.Davoudi, F.Kahraman Aliçavuş, FilizKhakpash, S.Esmer, E. M.Baştürk, O.https://hdl.handle.net/20.500.12428/37492022-12-05T11:34:51Z2021-01-01T00:00:00ZThe First Light Curve Solutions and Period Study of BQ Ari
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.
2021-01-01T00:00:00ZOptimization applied to selected exoplanetsNg, Shi YuanJiadi, ZhouPüsküllü, ÇağlarBanks, TimothyBudding, EdwinRhodes, Michael D.https://hdl.handle.net/20.500.12428/36952022-09-11T13:19:14Z2021-01-01T00:00:00ZOptimization applied to selected exoplanets
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.
2021-01-01T00:00:00Z