Iranian Journal of Astronomy and AstrophysicsIranian Journal of Astronomy and Astrophysics
http://ijaa.du.ac.ir/
Thu, 22 Mar 2018 18:11:22 +0100FeedCreatorIranian Journal of Astronomy and Astrophysics
http://ijaa.du.ac.ir/
Feed provided by Iranian Journal of Astronomy and Astrophysics. Click to visit.Noether Symmetry in f(T) Theory at the anisotropic universe
http://ijaa.du.ac.ir/article_84_22.html
As it is well known, symmetry plays a crucial role in the theoretical physics. On other hand, the Noether symmetry is a useful procedure to select models motivated at a fundamental level, and to discover the exact solution to the given lagrangian. In this work, Noether symmetry in f(T) theory on a spatially homogeneous and anisotropic Bianchi type I universe is considered. We discuss the Lagrangian formalism of f(T ) theory in anisotropic universe. The point-like Lagrangian is clearly constructed.The explicit form of f(T) theory and the corresponding exact solution are found by requirement of Noether symmetry and Noether charge. A power-law f(T), the same as the FRW universe, can satisfy the required Noether symmetry in the anisotropic universe with power- law scale factor. It is regarded that positive expansion is satisfied by a constrain between parameters.Sat, 30 Sep 2017 20:30:00 +0100Effect of random telegraph noise on entanglement and nonlocality of a qubit-qutrit system
http://ijaa.du.ac.ir/article_91_22.html
We study the evolution of entanglement and nonlocality of a non-interacting qubit-qutrit system under the eﬀect of random telegraph noise (RTN) in independent and common environments in Markovian and non-Markovian regimes. We investigate the dynamics of qubit-qutrit system for diﬀerent initial states. These systems could be existed in far astronomical objects. A monotone decay of the nonlocality (entanglement) is found in the Markov regime, while for non-Markovian noise, phenomena of sudden change (death) and revival occurs. We ﬁnd that the preserving nonlocality (entanglement) depends on initial state of the system in common and independent environments; so, we can not strictly conclude that independent or common environments are more robust against the noise.Fri, 31 Mar 2017 19:30:00 +0100Pulsating red giant and supergiant stars in the Local Group dwarf galaxy Andromeda I
http://ijaa.du.ac.ir/article_92_22.html
We have conducted an optical long-term monitoring survey of the majority of dwarf galaxies in the Local Group, with the Isaac Newton Telescope (INT), to identify the long period variable (LPV) stars. LPV stars vary on timescales of months to years, and reach the largest amplitudes of their brightness variations at optical wavelengths, due to the changing temperature. They trace stellar populations as young as ~ 30 Myr to as old as ~ 10 Gyr whose identification is one of the best ways to reconstruct the star formation history. The system of galactic satellites of the large Andromeda spiral galaxy (M31) forms one of the key targets of our monitoring survey. In this first paper in the series, we present the first results from the survey in the form of a census of LPV stars in Andromeda I (And I) dwarf galaxy. Photometry was obtained for 10585 stars in a 0.07 square degree field, of which 116 stars were found to be variable, most of which are Asymptotic Giant Branch (AGB) stars. Our data were matched to mid-infrared photometry from the Spitzer Space Telescope, and to optical catalogues of variable stars from the Hubble Space Telescope.Fri, 31 Mar 2017 19:30:00 +0100