DX Cygni: A triple system with mass transfer

A dozen of new precise times of eclipses were measured for the eclipsing binary DX Cygni as a part of our long-term observational project for studying neglected eclipsing binaries with a short orbital period. Based on a current $O-C$ diagram, we found for the first time that its period is increasing ($dP/P=1.68\times {10}^{-7}$ day/years) and that times of minima show also significant cyclical changes with a period of about 16 years, caused very probably by a third body orbiting the eclipsing pair. The minimal mass of this companion is 0.49 M_⊙. The light curve solution in Phoebe results to the typical Algol-type semidetached configuration where the secondary fills its Roche lobe. The temperature of primary component was fixed to $T_1=5300$ K according to its spectral type, which gives us $T_2=3330\pm 20$ K for the secondary. The photometric mass ratio was estimated $q=0.504\pm 0.012$. We also compare orbital parameters of selected known Algol-type eclipsing binaries with proven mass transfer and a third body.     

Thermodynamics under the extended uncertainty principle background: Q−ϕ criticality analysis

The study of thermodynamics in the background of the “extended uncertainty principle (EUP)” comes into interest in recent eras. In this article, we consider a charged black hole (BH) in higher dimensional space–time and present the thermodynamic parameters, based on a semiclassical framework, initially. Then we extend the same within the EUP background. We also analyze the $Q-\varphi$ criticality and find the critical points (${\varphi }_c,Q_c$ and $T_c$) when $Q-\varphi$ criticality appears. We study the effects of EUP on phase transition for higher dimensions ($d=5$) by plotting the $Q-\varphi$ diagrams. Further, we investigate the stability (thermal and global) of the BHs by employing the specific heat and the Gibbs free energy without and within EUP correction and compare the results with the Schwarzschild BHs in higher dimensions.     

Tsallis holographic dark energy model with observational constraints in the higher derivative theory of gravity

The present study deals with a Tsallis holographic dark energy model in a flat Friedmann-Lamatire-Rbertson-Walker space-time geometry in the context of higher derivative theory of gravity. We have solved the field equations by applying energy conservation-law in non-interacting case and have obtained such a scale factor $a\left(\tau \right)={\left[\sinh \left(\sqrt{2a_1}\tau \right)\right]}^{\frac{1}{2}}$ where $a_1$ is called as model parameter which shows transit phase evolution of the universe (decelerating to accelerating). Using this scale factor we have obtained the various cosmological parameters viz. Hubble parameter $H$, deceleration parameter (DP) $q$, jerk $j$, snap $s$, lerk $l$ and max-out $m$. Constraining on Hubble parameters $H\left(z\right)$ by the observational data of $H\left(z\right)$ we have obtained the present values of $H_0$, $a_0$ and $a_1$ and by using these constrained values, we have studied other cosmological parameters. Taking the constant equation of state (EoS) ${\omega }_m$ for ordinary matter, we have investigated the effective behaviour of various cosmological parameters and energy conditions in our model. We have observed the present values of $\{t_0,H_0,q_0,j_0,s_0,l_0,m_0,{\omega }_{d{e}_0},{\omega }_0^{\left(eff\right)}\}$ and discussed with $\Lambda$CDM model. We have found the age of the present universe $t_0=13.05$ Gyrs, present value of DP $q_0=-0.8065$ and transition point $z_t=0.748$ which are compatible with several observational results.     

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.