Journal of Astrophysics and Astronomy最新文献

The pulsation of white dwarfs provides crucial information on stellar parameters for understanding the atmosphere and interior structure of these stars. In this study, we present a comprehensive statistical analysis of known ZZ Ceti stars from historical literature. Our dataset includes stellar parameters and oscillation properties from 339 samples, with 194 of them having undergone asteroseismological analysis. We investigated the empirical instability strip of ZZ Ceti stars and confirmed the linear relationship between temperature and weighted mean pulsation periods (WMP). We found that the WMP distribution is well-described with two groups of stars with peak values at ({sim }254) and ({sim }719) s. Using seismic mass and trigonometrical radii derived from GAIA DR3 parallaxes, we tested the mass-radius relationship of white dwarfs through observational and seismic analysis of ZZ Cetis. They are generally larger than the theoretical values, with the discrepancy reaching up to ({sim }15)% for massive stars with a mass estimated by seismology.

Space weather poses significant risks to technical systems and the global economy, making it a critical area of research. Coronal mass ejections (CMEs) are the primary drivers of space weather and can cause intense geomagnetic disturbances. The solar wind (SW) governs CME propagation in the heliosphere and drives geomagnetic storm activities. Understanding the evolution of SW stream interaction regions (SIRs), CMEs, and their interactions in the inner heliosphere is essential for accurately predicting their arrival times and mitigating their impacts. This study presents a review of Space Weather Adaptive Simulation (SWASTi), an indigenous three-dimensional magnetohydrodynamic (MHD) modelling framework, with a focus on its SW and CME modules. Comparative analysis with in situ observations demonstrates the model’s robustness, revealing the significant role of ambient SW conditions in shaping the morphological and dynamical properties of CMEs. The geo-effective impact of CME-CME interactions are also explored with a particular focus on the recent Gannon storm. Furthermore, the study discusses how in situ measurements from the Aditya-L1 mission can synergise with the SWASTi framework. This integrated approach, leveraging Aditya-L1 data and SWASTi’s 3D MHD simulations, provides new insights into the complex behaviour of solar wind, SIRs, and CMEs, promising significant advancements in near-real-time space weather forecasting.

The Semnan University Radio Array (SURA) is a self-triggered radio array located on the roof of the Physics Faculty at Semnan University in Iran. It is designed to detect radio emissions from air showers generated by ultra-high energy (UHE) cosmic rays with energies exceeding (10^{17}) eV. The array consists of 4 Log-Periodic Dipole Antennas (LPDAs) operating in the 40–80 MHz range. In this study, we present a method for reconstructing the core location of extensive air showers (EAS) by comparing the signal intensities of simulated and experimental data. We employ a simulated dense array as a reference and determine the core location by matching the experimental signal intensity of each antenna with the corresponding reference antenna in the simulated dense array. The method is first validated using simulated events to estimate its accuracy. We then apply it to the cosmic ray candidates detected by the SURA. Our results show that the core location can be reconstructed with a minimum error of about 3 m. However, when the characteristics of the shower being reconstructed differ significantly from the reference array, the error increases. To enhance reconstruction precision and computational efficiency, we explore optimizations, including reducing the dense array size and accounting for variations in primary energy and arrival direction. Our findings demonstrate the potential of radio-based techniques for high-precision core location reconstruction, providing valuable insights for future large-scale cosmic ray observatories.

Geomagnetic storms are the result of interaction between Earth’s magnetic field and interplanetary magnetic field conducted by large-scale structures from the Sun, such as coronal mass ejections (CMEs) and stream interaction regions (SIRs). CMEs originate from closed magnetic regions on the Sun, such as active regions and quiescent filament regions. SIRs are formed in the interplanetary medium due to the fast solar wind originating from coronal holes—regions of open magnetic field lines and interacting with the slow wind ahead. Geomagnetic storms have significant space weather consequences, such as geomagnetically induced currents, atmospheric heating, ionospheric density changes and energization of Van Allen belt electrons to relativistic energies. In this paper, we describe a catalog of intense geomagnetic storms with the Dst index (le -)100 nT (https://cdaw.gsfc.nasa.gov/CME_list/dst100), which is obtained from the Dst data made available online by the World Data Center, Kyoto, Japan. The catalog contains detailed information on the solar source – whether a CME or a coronal hole, including the cases that are due to a combined action of the two. The catalog also provides detailed information on the CME sources and coronal holes. We also presented some statistical results derived from the catalog.

We aim to identify the cluster members, estimate cluster properties, study the dynamical state of the clusters as a function of mass, trace the existence of dynamical effects in massive stars, and check for spatial patterns of members in young clusters. We studied 14 young open clusters located within 1 kpc using the data from Gaia DR3 with the membership estimated using the GMM method. The cluster parameters, such as age, distance, metallicity, and extinction were estimated by fitting PARSEC isochrones to the CMDs. These clusters are found to have ages between 6 and 90 Myr, located between 334 and 910 pc, covering a mass range of 0.13–13.77 (hbox {M}_odot ). In five of these clusters, stars from F to M spectral type show increasing velocity dispersion, a signature for dynamical relaxation. We detect high proper motion for B and A-type stars, possible walkaway stars in the other five clusters, Alessi Teutsch 5, ASCC 16, ASCC 21, IC 2395, and NGC 6405. We demonstrate the existence of mass-dependent velocity dispersion in young clusters, suggestive of dynamical relaxation. The typical range of transverse velocity dispersion is found to be 0.40–0.70 km (hbox {s}^{-1}) for young clusters.

CubeSats present unique opportunities for observational astronomy in the modern era. They are useful in observing difficult-to-access wavelength regions and long-term monitoring of interesting astronomical sources. However, conventional telescope designs are not necessarily the best fit for the restricted envelope of a CubeSat. Additionally, fine-pointing stability on these platforms is difficult due to the low mass of the spacecraft, and special allocations within the optical design are needed to achieve stable pointing. We propose afocal telescope designs as the framework to realise imagers and low-resolution spectrographs on CubeSat platforms. These designs help reduce the number of components in the optical chain and aim to improve throughput and sensitivity compared to conventional designs. Additionally, they also provide a fine steering mechanism within a collimated beam section. Fine beam steering within the collimated beam section avoids issues of image degradation due to out-of-plane rotation of the image plane or offset in the rotation axis of the mirror. This permits using simple and mostly off-the-shelf tip-tilt mirrors for beam steering. The designs discussed here also allow for a standard telescope design to be used in many instrument types; thus reducing the complexity as well as the development time and cost. The optical design, performance, and SNR estimations of these designs, along with some interesting science cases, are discussed. Several practical aspects in implementation, such as guiding, tolerancing, choice of detectors, vibration analysis, and laboratory test setups, are also presented.

We investigate the phenomenon of clustering of galaxies in an expanding universe by applying the fluctuation theory. We evaluate the fluctuation moments for the number of particles as well as the correlated fluctuations for number and energy of particles (galaxies), clustering under their mutual gravitation. The correlated fluctuations (langle Delta NDelta Urangle ) show interesting results. The value of (langle Delta Nrangle ) can be both positive and negative, because it is the difference between N and the mean value of N. A negative (langle Delta Nrangle ) corresponds to regions of underdensity and a positive (langle Delta Nrangle ) corresponds to regions of overdensity, as described by the clustering parameter b. The present work is concerned with the region (bge 0), at which gravitational interaction has already started causing the galaxies to cluster. Thus, for this work, the value of (langle Delta Nrangle ) is positive. Similarly, the energy fluctuations (langle Delta Urangle ) can also be both positive and negative. For large correlations, the overdense regions typically have negative total energy, and the underdense regions have usually positive total energy. The critical value at which this switch occurs has been calculated analytically. The results obtained by fluctuation theory closely match those obtained earlier by specific heat analysis and Lee-Yang theory. The evaluation has been extended to multicomponent systems, having a variety of masses. It has been found that the gravitational clustering of galaxies is more sensitive to mass ratios and less sensitive to the number densities of galaxies. This means there is little effect of (nu ) (number density), but a significant effect of (mu ) (mass) of galaxies on the clustering phenomenon. The clustering of galaxies is quicker when the mass of individual galaxies increases. They become nuclei for condensation. As the mass of galaxies increases, the transition from positive to negative energy occurs at a higher stage of clustering than in a single-component system.

We present a multi-frequency analysis of the candidate double–double radio galaxy (DDRG) J2349−0003, exhibiting a possible lobe misalignment. High-resolution uGMRT observations at Bands 3 and 4 reveal a complex radio morphology featuring a pair of inner and outer lobes, and the radio core, while the Band 5 image detects the core and the compact components. The positioning of both pairs of lobes with the central core supports its classification as a DDRG. Spectral age estimates for the inner and outer lobes indicate two distinct episodes of active galactic nucleus (AGN) activity interspaced by a short quiescent phase. The possible compact steep-spectrum nature of the core, together with its concave spectral curvature, suggests ongoing or recent jet activity, suggesting the possibility that J2349−0003 may be a candidate triple-double radio galaxy. With a projected linear size of 1.08 Mpc, J2349−0003 is classified as a giant radio galaxy (GRG), although its moderate radio power ((sim ) (10^{24}) WHz(^{-1})) suggests a sparse surrounding environment. Arm-length ((R_theta )) and flux density ratios ((R_S)) indicate environmental influences on source symmetry. The observed lobe misalignment and the presence of nearby galaxies in the optical image suggest that merger-driven processes may have played a key role in shaping the source’s evolution.

We investigate the cosmological dynamics of an anisotropic Bianchi type-V universe in the framework of f(R, T) gravity with Tsallis holographic dark energy (THDE). By considering power law and exponential volumetric expansions, we analyze the evolution of key cosmological parameters and their implications for late-time acceleration. The model's behavior is examined through energy conditions, state finder diagnostics, and stability analysis. Our results indicate that the interplay between anisotropy, modified gravity, and THDE can produce a viable cosmic evolution, transitioning from deceleration to acceleration. To enhance the physical relevance, we compare our findings with observational Hubble data, providing preliminary parameter constraints. This study contributes to the understanding of alternative dark energy models. Our exponential model leads to perpetual acceleration as seen in a de Sitter universe.

This study employs a direct approach to construct transfer trajectories within photo-gravitational Sun–Earth system and by considering the Earth as an oblate primary in circular-restricted three-body problem (CRTBP). Specifically, it explores transfer trajectories of a spacecraft from an Earth-centred parking orbit to a halo orbit near Lagrangian point in photo-gravitational CRTBP framework. In this work, the Chebyshev collocation method (CCM) is used in combination with differential correction (DC) method to construct transfer trajectories. To compensate for the absence of a general analytical solution in the photo-gravitational CRTBP, this method uses the CCM to produce a trustworthy starting approximation. The DC method is then used to improve the approximation to the required precision for the trajectories. For a comprehensive analysis, we consider six times-of-flight (TOF) durations ranging from 100 to 200 days, with increments of 20 days (i.e., 100, 120, 140, 160, 180 and 200 days). For each TOF, we compute the departure velocities required from the Earth-centred parking orbit and the insertion velocities at the halo orbits. These computations enable us to generate detailed velocity profiles and assess the propulsive demands of different transfer durations. Additionally, we investigate the influence of out-of-plane amplitude ({A}_{z}) of the halo orbits on maneuver costs. We consider five halo orbits with varying values of ({A}_{z},(1.1times {10}^{5}, 2.0times {10}^{5}, 3.0times {10}^{5}, 4.0times {10}^{5}text{ and }5.0times {10}^{5}text{ km})) to analyse how the size and shape of halo orbit affect the required velocity changes (ΔV). The study quantifies the total velocity magnitude necessary for the spacecraft’s insertion onto the transfer path. We also implement the coordinate transformation of the state vector of spacecraft from the Sun–Earth barycentric rotating frame to the Earth-centred inertial J2000 frame.