New Astronomy最新文献

The light curves (LC(s)) of the shallow contact binary (SCB(s)) IR Vir were retrieved from the TESS, Kepler (K2), ASAS, ASAS-SN, and KWS databases and comprehensively analyzed in this paper. For IR Vir, a q search was conducted to determine the mass ratio, which was found to be $0.371\pm 0.008$. The analysis indicates that IR Vir was a typical A-type W UMa. Since the determination of absolute parameters is crucial for analyzing the evolution of such systems, the masses of the bodies of IR Vir were estimated as $M_1=1.03\pm 0.10$ M${}_{\odot }$, $M_2=0.38\pm 0.05$ M${}_{\odot }$, and the radii as $R_1=1.16\pm 0.06$ R${}_{\odot }$, $R_2=0.73\pm 0.04$ R${}_{\odot }$. In the analysis of the orbital period (OP(s)) for IR Vir, it was found that the OP of IR Vir was increasing, and this value was calculated to be 0.0376 s per year. The OP increase can be explained by the conserved mass exchange between the bodies, and it can be proposed to be from the low mass body to the more one. This value was calculated as $2.4\times 10^{-7}$ $M_{\odot }$ per year. Furthermore, a sinusoidal change in the OP was also identified, and it was proposed that this could be attributed to the presence of a third body or magnetic activity. Finally, to gain a better understanding of the nature of IR Vir, it was positioned in the logM${}_{tot}$ $-$ logJ and HR (Hertzsprung-Russell) diagrams.

We present light curve solution of V458 Mon firstly by using the Wilson-Devinney code. The total eclipse and deep minima of the light curves of V458 Mon enable us to determine reliable orbital parameters of the binary system. The solution suggests that V458 Mon is a low mass ratio binary system with about 0.2 possessing a moderate degree of contact. The long-term period investigation showed that the period of V458 Mon is increasing at $dP/dt=+2.59\times 10^{-7}days/yr$, which could be the reason of mass transfer from the less massive component to more massive primary one, together with a periodic change. The oscillation in orbital period may be due to an unseen tertiary companion with the mass about $M_3=1.8M_{\odot }$ . After removing these change, there is still a weak cyclic change maybe due to magnetic activity. With the increase in orbital period of binary, the separation increases and mass ratio decreases which eventually leads V458 Mon towards merger.

This paper studies the combined effects of radiation and galactic cosmic ray pressures on the gravitational instability of magnetized and rotating viscoelastic fluids. The dispersion relations are derived using the normal mode analysis and discussed in the hydrodynamic (weakly coupled fluid) and kinetic (strongly coupled fluid) limits. These dispersion relations are analyzed separately for transverse and longitudinal wave propagation modes. Jeans instability criteria are obtained for kinetic and hydrodynamic limits for both modes of wave propagation, and it is found that the critical Jeans wavenumbers in each case are modified due to the presence of viscoelastic effects, radiation and cosmic rays pressures, and Alfvên wave velocity. It is also observed that the radiation pressure, cosmic ray pressure and viscoelastic parameters suppress the growth rate and thus have stabilizing effects on the Jeans instability. However, cosmic ray diffusion has a destabilizing effect on the onset of gravitational instability. The effects of various parameters on the growth rate of instability are calculated numerically and the outcomes are depicted graphically. The results of the present analysis shall be helpful in understanding the impact of cosmic rays and radiative mechanisms on the gravitational collapse in the viscoelastic region of molecular cloud clumps.

In this paper, we explore the effect of the parameters of non-linear electrodynamics (NLED) and magnetic charges on various aspects of black holes (BH) arising in the particular NLED theory. More precisely, we look into the behavior of photons around the BH and produce shadow by considering a thin accretion disk model. We initially examine the overall behavior of the photon sphere and the corresponding shadow silhouette under the effects of these parameters. Using the EHT data for Sgr. A* and M87*, we provide constraints on the magnetic charge $q_m$. Our results indicate that M87* gives better constraints, and as the value of the NLED coupling parameter $\beta$ is increased, the constrained range for $q_m$ widens. At lower values of $q_m$, we find that the shadow radius is close to the observed value. Then, we study different other aspects, such as the energy emitted by the accretion disk, the temperature of the disk around the BH, and the nature of light it gives off. We also look at how the black hole shadow appears in different situations. Finally, we investigate how the magnetic charge affects all the above mentioned aspects when we take into account NLED along with gravity. This study helps us understand the complex relationship between magnetic charge and its effect on various aspects related to a BH.

In the present work we analyze a dynamical wormhole solution with two fluids system (one isotropic and homogeneous and the other being inhomogeneous and anisotropic in nature) as the matter at the throat. We choose two different forms of Equation of State(EoS) and investigate two solutions of the wormhole geometry. The properties to ensure existence and traversability has been analyzed. Also, the model of the dynamic wormhole has been examined for a possibility of the Emergent Universe(EU) model in cosmological context. Finally, for the dynamical wormholes so obtained, Null Energy Condition(NEC) has been examined near the throat.

Stellar orbits and the evolution of galaxies are intertwined processes that have long-term implications on each other. This paper studies how stellar orbits at the galaxy’s central region are disturbed by an asymmetric dark matter halo potential. Evidence from the observations and simulations in the Milky Way type galaxy suggests that the center of the dark matter halo could be off-centered by a few parsecs concerning the center of the core. The equations of motion of stars in the core of galaxies are expressed in terms of three-dimensional perturbed potential arising from the offset halo. The central region’s azimuthal variation in the effective potential is obtained and the first-order epicyclic theory is used to solve for the orbits. The magnitude of this perturbation potential grows at small radii and exhibits $m=1$ azimuthal fluctuations. In the central region, within 3 kpc radius, even a small halo offset of 300 pc can cause a surprisingly strong spatial and kinematical lopsidedness. A planar orbit, initially assumed to be in disc plane, tends to leave the plane giving rise to non-planar configuration. Furthermore, as long as the halo offset persists, the central region will stay lopsided. The dark matter halo would significantly impact the dynamic development of this region and could help fuel the active galactic nucleus.

We study the dynamics in the outer regions of a rotating barred galaxy and in particular, we observe the escape of a test particle from the gravitational potential of the galaxy. The acceleration mechanism of the test particle is a close encounter with one of the ends of the bar with the right relative phase of the position of the bar. This is a possible mechanism for the creation of high-velocity stars, i.e. stars with an energy sufficient to escape from the galaxy. Our results suggest that good candidates for high-velocity stars accelerated by this mechanism are the old low-mass high-velocity stars moving close to the disc. We will encounter the asymptotic dynamics which leads naturally to the study of a type of Poincaré map which can be reinterpreted as a scattering map. Thereby an iterated scattering map enters the picture in a quite natural form. The present work is a supplement to previous work on the dynamics in the inner region of the same model.

We model the TESS light curve of the binary system RX Dra, and also first calculate a lot of theoretical models to fit the g-mode frequencies previously detected from the TESS series of this system. The mass ratio is determined to be $q$=0.9026${}_{-0.0032}^{+0.0032}$. We newly found that there are 16 frequencies (F1–F7, F11–F20) identified as dipole g-modes, two frequencies (F21, F22) identified as quadrupole g-modes, and another two frequencies (F23, F24) identified as g-sextupole modes, based on these model fits. The primary star is newly determined to be a $\gamma$ Dor pulsator in the main-sequence stage with a rotation period of about 5.7${}_{-0.2}^{+0.7}$ days, rotating slower than the orbital motion. The fundamental parameters of two components are firstly estimated as follows: $M_1$=1.53${}_{-0.17}^{+0.00}$ M ${}_{\odot }$, $M_2$= 1.38${}_{-0.00}^{+0.18}$ M ${}_{\odot }$, $T_1$=7240${}_{-44}^{+490}$ K, $T_2$=6747${}_{-221}^{+201}$ K, $R_1$=1.8288${}_{-0.0959}^{+0.0260}$ R ${}_{\odot }$, $R_2$= 1.3075${}_{-0.2543}^{+0.0450}$ R ${}_{\odot }$,