Journal of Astrophysics and Astronomy最新文献

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.

A recent study announced the detection of three bands in the ultraviolet emission spectra of more than a dozen comets, assigning two of them to pentacene (C(_{22})H(_{14})) and the third one to toluene (C(_7)H(_8)). The comparison of the spectra with the results of exploitable laboratory measurements on rare-gas-matrix-isolated pentacene and jet-cooled toluene does not reveal any elements that justify the assignment, which is therefore unsubstantiated. The study also claimed the detection of an Fe ii line in the gas of all but one comet. Yet, spectroscopic data on Fe(^+) do not corroborate the attribution. Because spectroscopic measurements on the ultraviolet emission of pentacene in the gas phase are not available, this work also presents a synthetic spectrum of the S(_5rightarrow textrm{S}_0) transition relevant to the wavelength range of the observations. Calculated using density functional theory and its time-dependent extension, the synthetic spectrum may facilitate the search for pentacene fluorescence in cometary spectra until laboratory measurements are accessible.

Understanding thermal and turbulence properties of interplanetary coronal mass ejections (ICMEs) is essential for analysing their evolution and interactions with the surrounding medium. This study explores these characteristics across different regions of two distinct ICMEs observed at 1 AU, utilizing in situ measurements from the Wind spacecraft. Polytropic indices ((Gamma _e) for electrons and (Gamma _p) for protons) reveal significant deviations from adiabatic expansion, suggesting sustained heating mechanisms within the ICMEs even at 1 AU. Effective polytropic index ((Gamma _{text {eff}})) of the magnetic ejecta (ME) in both ICME1 and ICME2 is found to be near-isothermal ((Gamma _{text {eff}} = 0.88) and 0.76), aligning with measurements near the Sun, highlighting consistent heating across heliospheric distances. Spectral analysis at the inertial scale reveals Kolmogorov-like turbulence in the fast ICME1’s ME, while ME of the slower ICME2 exhibits less-developed turbulence with a shallower spectral index ((alpha _B)). Turbulence analysis in the dissipation scale indicates that the ME of slower ICME2 is less affected by the ambient medium than the faster ICME2. The MEs of both ICMEs show magnetic compressibility much smaller than unity ((C_B<1)), suggesting dominant Alfvénic fluctuations in the MEs. Notably, the partial variance of increments (PVI) method identifies more intermittent structures, such as current sheets and reconnection sites, in sheath and post-ICME regions. Higher PVI values correlate with regions of increased electron and proton temperatures (for the sheath region) as well as higher (C_B) values, highlighting their role in local energy dissipation. These results enchance the importance of ongoing heating and turbulence processes in shaping the evolution of ICMEs.

Fermi Large Area Telescope (Fermi-LAT) observations reveal a significant population of blazars, and recent astrophysical research has focused on exploring flux variations in blazars. Up to now, Fermi-LAT has discovered a significant number of blazars, displaying quasi-periodic behaviour. In this study, Fermi-LAT data is utilized to construct the (gamma )-ray light curve for blazar J0811.4(+)0146 spanning from August 2008 to November 2024, covering 16 years of observations. Four distinct methods, namely, Lomb–Scargle periodogram (LSP), Weighted wavelet Z-transform (WWZ), discrete correlation function (DCF) and Jurkevich (JV), are employed to investigate (gamma )-ray emissions from this blazar in detail. The analysis reveals quasi-periodic oscillation (QPO) behaviour with a period of (4.35 pm 0.34) years. Significance of this QPO is assessed using Monte Carlo simulations, which indicate a significance level of 4.5(sigma ). This study suggests that the detected QPO can be plausibly explained by Newtonian-driven jet precession associated with a supermassive black hole binary system (SMBHB). Utilizing this model, we estimate, mass of the primary black hole to be (7.3 times 10^9 textrm{M}_{odot }), mass of the secondary black hole to be (2.1 times 10^9 textrm{M}_{odot }) and (frac{R_{1}}{R_{2}}) to be 0.27, resulting in an orbital period of the secondary black hole ((P_{M_2})) of 1.15 years and a precession period of the jet of (sim )42.49 years.

The detection of gravitational waves (GW) by the LIGO-Virgo-KAGRA (LVK) network has opened up a new era in astrophysics. The identification of the electromagnetic counterparts of GW sources is crucial for multi-messenger astronomy, one way of which is to use galaxy catalogues to guide optical follow-up observations. In this paper, we test the utility of a galaxy-targeted approach with mass prioritised galaxy ranking for the ongoing LIGO O4 run. We have used the simulated results for the expected LIGO O4 events and the NED-LVS galaxy catalogue, and based our study on small field of view telescopes, specifically the GROWTH-India Telescope (GIT). With the increase in sensitivity of LIGO/Virgo in the ongoing observing run O4, the expected number of total detections have gone up, but most of these are also now poorly localised. We show that a larger volume covered in the same field-of-view (FoV) on the sky results in a large increase in the total number of galaxies in each FoV. A significant top-heaviness is observed in the mass-ranked list of galaxies, which still numbers a few thousand in most cases. At larger distances, such high numbers of deep follow-up observations are infeasible in most cases, rendering galaxy catalogues useful in limited cases. However, these are still useful at lower distances where LVK detectors are currently sensitive and where galaxy completeness is higher. We also explore the effect of mass-filling to account for galaxy catalogue incompleteness at large distances. If mass-filled probabilities are considered as the metric for ranking and coverage, we find that the conventional 2D probability search performs better than a 3D galaxy catalogue (without mass-filling) based search at distances larger than 300 Mpc (up to which NED-LVS is ({sim } 70)% complete), and using 3D mass times probability in each tile performs better for nearby events.

I explore models of the dust-scattered component of the cosmic ultraviolet background (CUVB) at the north galactic pole (NGP) to develop a framework for calculating the dust-scattered light as a function of the optical depths. As expected, I find that the dust-scattered emission scales linearly, with reddening up to (E(B-V) approx 0.1) mag and derive a parametric model for this dependence. I have applied these models to fit the far-ultraviolet (1350–1800 Å) observations from the galaxy evolution explorer (GALEX) finding that the optical constants of the interstellar dust grains—albedo (a) and phase function asymmetry factor (g)—are consistent with predictions from the Astrodust model ((a = 0.33), (g = 0.68)). I detect an isotropic offset of (267 pm 7) ph cm(^{-2}) s(^{-1}) sr(^{-1}) Å(^{-1}), half of which remains unaccounted for, by known Galactic or extragalactic sources. I will now extend my analysis to wider sky regions with the goal of generating high-resolution extinction maps.