Journal of Astrophysics and Astronomy最新文献

The response of topside ionosphere over low and midlatitudes to the severe geomagnetic storm of 23–24 April 2023 are studied using in-situ plasma measurements made by the Swarm satellite constellation at altitudes of 470 and 510 km. The local time coverage during the period was on dawn and dusk sectors. The geomagnetic storm is a two-step storm reaching a minimum SYM-H index magnitude of −233 nT. Observations reveal positive ionospheric storm with plasma density enhancements during sunlit periods of the main phase of the geomagnetic storm. This enhancement is significant over the Southern hemisphere. A clear increase in the equatorial electric field due to prompt penetration field is inferred through the increased separation of EIA crests and plasma density enhancements. This event showcased a longlasting prompt penetration electric field covering both the main phases. Interestingly, during the temporary recovery phase between the first and second main phases, the ionospheric observations are similar to those in the main phases with no indication of an overshielding electric field. During predawn hours of temporary recovery phase, a negative ionospheric storm is observed only over low latitudes. During the recovery phase, disturbed dynamo effects are also observed. However, for the first five hours in the early recovery phase, the effects were still similar to that of main phase. While the ring current recovery indicated by SYM-H indices took more than 36 hours, the disturbance dynamo effects were seen in the ionosphere only for about 11 hours, and the ionosphere was behaving similar to the quiet periods after 16 hours of start of the recovery phase. The observations are explained by means of undershielding prompt penetration electric fields during the main phases and development of disturbed dynamo effect well into the recovery phase.

In our previous work, we proposed a special Lorentz violation model characterized by the fact that the maximum energy of a particle with mass is finite and proportional to its rest mass, rather than infinite as predicted by the Lorentz model. In this paper, we continue to investigate the impact of the Lorentz violation model on the curved spacetime. Firstly, we proposed a method to obtain the spacetime metric corresponding to this Lorentz violation model. Secondly, we used this new metric to analyze the proper acceleration of particles fixed in the Schwarzschild spacetime. To our surprise, we find that when the distance between particles and the event horizon of the Schwarzschild black hole is less than a certain distance, the smaller the distance, the smaller the proper acceleration, and the proper acceleration tends to 0 when the particle is fixed at the event horizon. By analogy with the quark model in particle physics, we can also call this phenomenon the "asymptotic freedom" in Schwarzschild spacetime, which shows us a different black hole.

We consider the effects of Lorentz-breaking and dark energy by introducing both into the action of scalar and spinor field. Through the variational principle, we derive modified dynamic equations for bosons and fermions expressed in Hamilton-Jacobi-like forms. Focusing on a non-rotating KSK black hole surrounded by holographic quintessence, a configuration inspired by Kiselev and Kazakov-Solodukhin’s theoretical frameworks, we investigate the quantum tunneling rates of bosons and fermions at the event horizon of the black hole. The modified Hawking temperature and Bekenstein-Hawking entropy of this black hole are systematically examined. Our analysis reveals how dark energy parameters and Lorentz-violation coefficients influence the thermodynamic quantities, thereby enriching the understanding of black hole thermodynamics. This study provides new insights into the interplay between quantum effects, spacetime symmetry breaking, and dark energy in black hole physics.

Resonant periodic orbits are investigated in binary star systems with three bodies. Kepler-34, Kepler-35, Kepler-413, and Kepler-16 are chosËen and surface of sections of Poincaré (SSP) is utilized in this study. As the mass ratio decreases, the amplitude of the stability regions decreases and for smaller mass ratios, the structure of the phase plane differs significantly from that observed at higher mass ratios. Using the technique of SSP, locations of the resonant periodic orbits 9:7, 7:5, 3:2, 4:3, 5:3, 1:1, and 2:3 are explored. The starting point and path of the periodic orbits around the primary are analysed for different radiation force and Jacobi constant values. The radiation pressure of the bigger primary has no effect on the resonance order. The position of the periodic orbits, however, fluctuates and significant variations in the eccentricity are observed. The inclusion of the radiation force causes the periodic orbits of resonance 9:7, 7:5, 3:2, 4:3, 5:3, 1:1 and 2:3 around the larger primary to shift in the direction of the smaller primary. Periodic orbits are used to investigate tiny binary system bodies, such comets and asteroids, whose motion can be strongly influenced by solar radiation pressure.

Radiation and high-energy particles linked to solar activity around sunspots, including solar flares and coronal mass ejections (CMEs), can be harmful to living organisms. Major geomagnetic storms (GSs) might weaken the geomagnetic field, allowing energetic particles to penetrate the Earth's magnetosphere. Thus, analyzing corresponding solar flares or CMEs provides geoeffective parameters that help in predicting GSs. The purpose of the present study is to compare the geoeffectiveness of interplanetary features associated with DH type II burst-linked Halo CMEs (DH-HCMEs) and those not associated with DH type II bursts (Non-DH-HCMEs). In this study, it was observed that plasma flow pressure (FP) and flow speed (FS) attain their maximum values either before or during the main phase of the GS for both DH-HCMEs and Non-DH-HCMEs. We observed that the maximum values of FS and FP during solar cycle 23 (SC23), solar cycle 24 (SC24), and solar cycle 25 (SC25) are directly correlated with the lowest value of the Dst index for both DH-HCMEs and Non-DH-HCMEs. The analysis further showed that the Dst index decreases more significantly with increasing maximum solar wind speed (Vmax) of the disturbance across all three solar cycles, for moderate, intense, and severe GSs. Additionally, the Vmax associated with DH-HCMEs was consistently higher than that of Non-DH-HCMEs. We found that storm intensity is primarily driven by FP, with higher FP resulting in a more negative Dst index. Different FS regimes were also observed to have an impact on the value of the Dst index. In particular, during DH-HCME events in 2001 and 2005, we noted that when the Dst index rapidly dropped to its minimum—indicating a high rate of change of Dst index—FP did not decrease but instead remained relatively stable at a higher value. Since 2001 and 2005 were highly active years in SC23, the enhanced solar activity likely contributed to the occurrence of more energetic and faster Halo CMEs.

The goal of this work is to develop physical models for spherically symmetric systems in the realm of f(Q) gravity. The field equations are set up for an anisotropic fluid, and formulate these equations using the physical ansatz of the Vaidya–Tikekar solution. The intrinsic constants of the model can be ascertained by matching the interior solution to the external Schwarzschild solution. The use of accessibility conditions helps to understand the physical viability of the obtained model. LMC X-4 pulsar is used as a toy model to test the viability of the model, and Mathematica software is used for deeper insights and visualisation of the physical parameters against fixed values of constants.

The meteor occurrence height and decay time height are strongly dependent on local atmospheric conditions in the mesosphere and lower thermosphere region. In this study, we comparatively examine the seasonal behaviour of vertical distribution of meteor occurrence height and decay time height at two identical radars of conjugate polar latitudes, Esrange ((68^circ )N) and Rothera ((68^circ )S). To understand the nature of meteor trail variations, the received signal power is categorised into two groups, weak and strong echoes, and their seasonal mean vertical profiles are constructed. It has been noticed that the meteor occurrence height shows a seasonal symmetry; however, the decay time vertical profiles show an asymmetric pattern at conjugate polar latitudes, particularly for strong echoes. Seasonally, there is about 1 km difference in the occurrence height and decay time height of weak and strong echoes. From the decay time vertical profiles, it has been noticed that the decay time turning altitude (i.e., inflection point) varies seasonally in the altitude range of 80–86 km for weak and strong echoes. The maximum turning altitude of about 85 km is observed in Northern winter at Esrange ((68^circ )N) and in Southern summer at Rothera ((68^circ )S); similarly, the minimum turning altitude of about 80 km is observed in Northern winter at Esrange ((68^circ )N) and in Southern summer at Rothera ((68^circ )S). The probable reasons for such behaviour of meteor trails at opposite polar latitudes are discussed.

A strictly linear evolution of the cosmological scale factor is surprisingly an excellent fit to a host of cosmological observations. Any model that can support such a coasting presents itself as a falsifiable model as far as classical cosmological tests are concerned. Such evolution is known to be comfortably concordant with the Hubble diagram as deduced from data of recent observations of low and high redshift objects, it passes constraints arising from the age and gravitational lensing statistics, and clears basic constraints on nucleosynthesis. Such an evolution exhibits distinguishable and verifiable features for the recombination era. This article discusses the concordance of such an evolution in relation to minimal requirements for large-scale structure formation and cosmic microwave background anisotropies along with the overall viability of such models. While these results should be of interest for a host of alternative gravity models that support a linear coasting, we conjecture that a linear evolution would emerge naturally either from General Relativity itself or from a General Relativistic theory of a non-minimally coupled scalar field theory.

The acceleration of cosmic expansion is a challenging problem in contemporary cosmology, drawing the attention of cosmologists. In relation to the subtle nature of the phenomenon in question, theories beyond general relativity abound to accommodate it in their purviews. f(R) models of gravity still offer a promising choice both at local and global horizons. In this study, we conduct a study of the accelerated cosmic expansion observed since the late-time era of the universe’s evolution, specifically within the context of f(R) gravity, which modifies the geometry of cosmic spacetime. By considering an f(R) model, we investigate first its viability conditions concerning radiation and matter eras and then follow a dynamical system approach to the analysis of the model. The dynamical system, under various conditions arising from the model using the variables m and r, is solved for fixed points, over which studying the stability properties of the system leads to the desired results. The parameters describing the densities of radiation, matter, and geometric curvature are calculated in each corresponding case. Through eigenvalues corresponding to the fixed points, we infer whether the system is stable or unstable. Apart from this, we consider all possible cosmic factors to assess the impact of their presence, as well as their individual and interactive effects. We observe that within the model, the critical points, corresponding eigenvalues, and the state parameter collectively justify the accelerating expansion, regardless of the dark energy considered. We also study the Lyapunov stability by linearising nonlinear systems and investigating how phase space analysis retains stability against small perturbations.

The study presents a detailed spectroscopic analysis of the planetary nebulae (PNe) NGC 2392 and NGC 4361 using optical spectra obtained from the 2-m Himalayan Chandra Telescope (HCT) and mid-infrared spectra from archival Spitzer IRS data. The physical conditions, such as electron temperature ((T_e)) and density ((n_e)), were derived using diagnostic emission lines through the PyNeb software. Elemental abundances of key species, including He, O, N, Ne, S, Cl, and Ar, were determined for both nebulae, offering insights into their nucleosynthesis history and evolutionary status. High-resolution HST and Pan-STARRS imaging further elucidate the morphological structures of the nebulae. NGC 2392 exhibits a well-defined double-shell structure and moderate excitation characteristics, while NGC 4361 displays a diffuse elliptical morphology with high-excitation conditions and a notably low nitrogen content. The observed line spectra and derived abundances point toward distinct progenitor histories for the two PNe, with NGC 2392 originating from a younger, intermediate-mass progenitor, while NGC 4361 traces an older, metal-poor Population II star. This comparative study enhances our understanding of the evolution and chemical enrichment processes of low- to intermediate-mass stars.