Weak gravitational lensing of black hole from T-duality in plasma

In this study, we investigate the impact of a plasma environment on gravitational weak lensing around a black hole from the perspective of T-duality. Our results demonstrate that the deflection angle of light rays around the black hole is notably affected by the parameter $l_0$, with an increase leading to a decrease in the deflection angle, while the effect of plasma on the deflection angle is the opposite. We also consider different types of plasma distributions, including uniform ${\omega }_e=const$, Singular Isothermal Sphere medium, and Non-Singular Isothermal gas sphere plasma. We have analyzed the total magnification of the image source due to gravitational weak lensing, taking into account the effect of parameter $l_0$ related to T-duality in the presence of plasma around the black hole.     

Relativistic isotropic stellar model in f(R,T) gravity with Durgapal- IV metric

In this work, a new static, non-singular, spherically symmetric fluid model has been obtained in the background of $f(R,T)$ gravity. Here we consider the isotropic metric potentials of Durgapal-IV (Durgapal, 1982) solution as input to handle the Einstein field equations in $f(R,T)$ environment. For different coupling parameter values of $\chi$, graphical representations of the physical parameters have been demonstrated to describe the analytical results more clearly. It should be highlighted that the results of General Relativity (GR) are given by $\chi =0$. With the use of both analytical discussion and graphical illustrations, a thorough comparison of our results with the GR outcomes is also covered. The numerical values of the various physical attributes have been given for various coupling parameter $\chi$ values in order to discuss the impact of this parameter. Here we apply our solution by considering the compact star candidate LMC X-4 (Rawls et al., 2011) with mass $=(1.04\pm 0.09)M_{\odot }$ and radius $=8.301_{-0.2}^{+0.2}$ km. respectively, to analyze both analytically and graphically. To confirm the physical acceptance of our model, we discuss certain physical properties of our obtained solution such as energy conditions, causality, hydrostatic equilibrium through a modified Tolman–Oppenheimer–Volkoff (TOV) conservation equation, pressure–density ratio, etc. Also, our solution is well-behaved and free from any singularity at the center. From our present study, it is observed that all of our obtained results fall within the physically admissible regime, indicating the viability of our model.     

First comprehensive study of W-type W UMa eclipsing binary V1036 Her

CCD photometry of the eclipsing binary system V1036 Her was performed using Johnson V filter in Dr. Mojtahedi Observatory of the University of Birjand during July-August 2017 and July 2018. Moreover, the spectroscopy of the system was carried out by TRES during April 2018. A mass ratio of $3.07\left(27\right)$is obtained and an initial effective temperature of 5500 was suggested. For the first time, the relative and absolute parameters of the system are determined by analyzing the light curve and radial velocity data. The results indicate that V1036 Her is a W-subtype W UMa system with a degree of overcontact of 22%. The analysis of the period change shows that the period of the system changes with the rate of $\dot{P}=2.23\left(4\right)\times {10}^{-7}\text{day}/\text{year}$. With the assumption of the system mass conservation, a mass transfer rate from the primary to the secondary component of ${\dot{m}}_1=1.00\left(3\right)\times {10}^{-7}{M}_{\odot }/\mathit{year}$ is probable. Additionally, a periodic behavior with a period of about 10 years is observed in the O-C curve, which predicts the possibility of a third body with a minimum mass of $0.14\left(1\right)M_{\odot }$.     

Inflationary anisotropic phases with bianchi-I cosmic model

This paper is devoted to studying warm anisotropic inflation using modified Chaplygin gas in the context of the Bianchi-I comic model. We investigate the dynamics of the warm intermediate universe model in two distinct regimes, i.e., weak and strong regimes in the context of generalized dissipative coefficient. We formulate solutions of dissipation coefficient, inflaton field, scalar & tensor (S/T) power spectra, spectral index in an environment of slow-roll approximation to discuss the existence of warm weak and strong inflation and checked their viability in view of 2018 Planck data. It is seen through graphical representation that the condition for the existence of warm weak inflation is preserved only for $z=0$ and $z=1$ whereas in the case of the strong dissipative regime, the compatibility is achieved for $z=3$. The corresponding decay rates and the S/T are found to be consistent with the current observations.     

Halo Meteors

The stellar halo contains some of the oldest stars in the Milky Way galaxy and in the universe. The detections of ‘Oumuamua, CNEOS 2014-01-08, and interstellar dust serve to calibrate the production rate of interstellar objects. We study the feasibility of a search for interstellar meteors with origins in the stellar halo. We find the mean heliocentric impact speed for halo meteors to be $\sim 270\text{km}{\mathrm{s}}^{-1},$ and the standard deviation is $\sim 90\text{km}{\mathrm{s}}^{-1},$ making the population kinematically distinct from all other meteors, which are an order-of-magnitude slower. We explore the expected abundance of halo meteors, finding that a network of all-sky cameras covering all land on Earth can take spectra and determine the orbits of a few hundred halo meteors larger than a few mm per year. The compositions of halo meteors would provide information on the characteristics of planetary system formation for the oldest stars. In addition, one could place tight constraints on baryonic dark matter objects of low masses.     

Presence of C2 molecular Lines in Sunspot Umbral Spectra

The C₂ molecule is well known for its astrophysical importance. The radiative transition parameters that include Franck-Condon (FC) factor, r-centroid, electronic transition moment, Einstein coefficient, absorption band oscillator strength, effective temperatures and radiative life time have been estimated for the Swan band $(d^3{\Pi }_g-a^3{\Pi }_u)$ system of C₂ molecule for experimentally observed vibrational levels using RKR (Rydberg–Klein–Rees) potential energy curve. The lifetime for the d³Π_g state of C₂ molecule was found to be 82.36 ns for the $v^{\prime }=0$ level. A reliable numerical integration method has been used to solve the radial Schrödinger equation for the vibrational wave functions of upper and lower electronic states based on the latest available spectroscopic data and known wavelengths. The estimated radiative transition parameters are tabulated. The effective vibrational temperature of Swan band system of C₂ molecule is found agreed with the effective rotational temperature from photosphere spectrum. Hence, the radiative transition parameters and effective temperatures help us to ascertain the presence of C₂ molecule in the interstellar medium, photosphere and sunspots.     

Photometric Follow-up Transit (Primary Eclipse) Observations of WASP-43 b and TrES-3b and A Study on Their Transit Timing Variations

Two photometric follow-up transit (primary eclipse) observations on WASP-43 b and four observations on TrES-3 b are performed using the Xuyi Near-Earth Object Survey Telescope. After differential photometry and light curve analysis, the physical parameters of the two systems are obtained and are in good match with the literature. Combining with transit data from a lot of literature, the residuals (O ? C) of transit observations of both systems are fitted with the linear and quadratic functions. With the linear fitting, the periods and transit timing variations (TTVs) of the planets are obtained, and no obvious periodic TTV signal is found in both systems after an analysis. The maximum mass of a perturbing planet located at the 1:2 mean motion resonance (MMR) for WASP-43 b and TrES-3 b is estimated to be 1.826 and 1.504 Earth mass, respectively. By quadratic fitting, it is confirmed that WASP-43 b may have a long-term TTV which means an orbital decay. The decay rate is shown to be P? = (?0.005248 ± 0.001714) s·yr^?1, and compared with the previous results. Based on this, the lower limit of the stellar tidal quality parameter of WASP-43 is calculated to be ${Q^{\prime }}_{*}\ge 1.5\times {10}^5$, and the remaining lifetimes of the planets are presented for the different ${Q^{\prime }}_{*}$ values of the two systems, correspondingly.     

Fluctuational mechanism for the formation of proton vortices in the superfluid core of neutron stars

The Gibbs thermodynamic potential of a proton vortex interacting with the normal core of a neutron vortex of radius r << λ (λ is the penetration depth) that is parallel to it and has an outer boundary of radius b is calculated. It is shown that, under this assumption, the capture of only one vortex by the core is energetically favorable. The force acting on the proton vortex owing to the entrained current is found and it is always directed toward the core. The corresponding force for a proton antivortex is directed toward the outer boundary of the neutron vortex. The Ginzburg-Landau equation is solved for a vortex-antivortex system and its Gibbs function is calculated. It is shown that at large distances from the core, vortex-antivortex pairs can form because of fluctuations. Acted on by the entrainment current, the antivortex moves outward, while the vortex stays inside the neutron vortex. It is shown that the best conditions for fluctuational pair production, followed by separation, exist near the outer boundary. It is shown that new proton vortices can develop only in a region where the entrainment magnetic field strength H (ρ) > H_C1 (H_C1 is the lower critical field). __________ Translated from Astrofizika, Vol. 51, No. 1, pp. 139–149 (February 2008).     

Turbulence Diffusion and Energy Spectrum Analysis of Large-scale Current Sheets in Flares

Magnetic reconnection (MR) is one of the most important physical processes for many dynamical phenomena in the universe. Magnetohydrodynamical (MHD) simulation is an effective way to study the MR process and the physical pictures related to the MR. With different parameter setups, we investigate the influences of the Magnetic Reynolds number and spatial resolution on the reconnection rate, numerical dissipation, and energy spectrum distribution in the MHD simulation. We have found that the magnetic Reynolds number $R_m$ has definite impact on the reconnection rate and energy spectrum distribution. The characteristic time for entering into the non-linear phase will be earlier as the Reynolds number increases. When it comes to the tearing phase, the reconnection rate will increase rapidly. On the other hand, the magnetic Reynolds number affects significantly the Kolmogorov microscopic scale $l_{\mathit{ko}}$, which becomes smaller as $R_m$ increases. An extra dissipation is defined as the combined effect of the numerical diffusion and turbulence dissipation. It is shown that the extra dissipation is dominated by the numerical diffusion before the tearing mode instability takes place. After the instability develops, the extra dissipation rises vastly, which indicates that turbulence caused by the instability can enhance the diffusion obviously. Furthermore, the energy spectrum analysis indicates that $l_{\mathit{ko}}$ of the large-scale current sheet may appear at a macroscopic MHD scale very possibly.     

Magnetohydrodynamic simulations of gamma-ray burst jets: Beyond the progenitor star

Achromatic breaks in afterglow light curves of gamma-ray bursts (GRBs) arise naturally if the product of the jet’s Lorentz factor $\gamma$ and opening angle ${\Theta }_j$ satisfies $\gamma {\Theta }_j?1$ at the onset of the afterglow phase, i.e., soon after the conclusion of the prompt emission. Magnetohydrodynamic (MHD) simulations of collimated GRB jets generally give $\gamma {\Theta }_j?1$, suggesting that MHD models may be inconsistent with jet breaks. We work within the collapsar paradigm and use axisymmetric relativistic MHD simulations to explore the effect of a finite stellar envelope on the structure of the jet. Our idealized models treat the jet–envelope interface as a collimating rigid wall, which opens up outside the star to mimic loss of collimation. We find that the onset of deconfinement causes a burst of acceleration accompanied by a slight increase in the opening angle. In our fiducial model with a stellar radius equal to ${10}^{4.5}$ times that of the central compact object, the jet achieves an asymptotic Lorentz factor $\gamma ～500$ far outside the star and an asymptotic opening angle ${\Theta }_j?0.04\text{rad}?2°$, giving $\gamma {\Theta }_j～20$. These values are consistent with observations of typical long-duration GRBs, and explain the occurrence of jet breaks. We provide approximate analytic solutions that describe the numerical results well.     

Photon in a cavity – a Gedankenexperiment

The inertial and gravitational mass of electromagnetic radiation (i.e., a photon distribution) in a cavity with reflecting walls has been treated by many authors for over a century. After many contending discussions, a consensus has emerged that the mass of such a photon distribution is equal to its total energy divided by the square of the speed of light. Nevertheless, questions remain unsettled on the interaction of the photons with the walls of the box. In order to understand some of the details of this interaction, a simple case of a single photon with an energy $E_{\nu }=h\nu$ bouncing up and down in a static cavity with perfectly reflecting walls in a constant gravitational field $\mathit{g}$, constant in space and time, is studied and its contribution to the weight of the box is determined as a temporal average.