Astrophysics and Space Science最新文献

In this paper we explore a unified cosmological framework combining variable generalized Chaplygin gas (VGCG) and gravitationally–induced adiabatic matter creation cosmology within the context of (f(Q)) gravity. Theoretical and statistical analyses are performed with two functional forms, (f(Q)=n_{1} Q^{k}) and (f(Q)=n_{0}+n_{1}Q^{k}), where (n_{0}), (n_{1}) and (k) are dimensionless free parameters. Using the latest observational data sets we perform a robust statistical analysis to constrain the model’s parameters. A statistical comparison, including goodness-of-fit with standard (Lambda )CDM model is performed. The results show that the Bayesian inference favors the complex models while the model selection criterion, like Akaike information criteria (AIC) and Bayesian information criteria (BIC) favor the simpler (Lambda )CDM model. The results also show a smooth transition from deceleration to acceleration around the redshift (z approx 0.6) with effective equation of state parameter remains in the quintessence regime. The present value of Hubble parameter align closely with Planck 2018 measurements.

We investigate late–time cosmology in the Finsler–Barthel–Kropina framework, where anisotropic effects are introduced into the FLRW background through a time–dependent function (eta (t)) constructed via the osculating Riemannian approach. The resulting modified Friedmann equations generate direction–dependent corrections to the expansion history. Using Cosmic Chronometers (CC), DESI BAO, and Pantheon+ supernova observations, we reconstruct the Hubble rate, energy density, and key cosmographic quantities. The model yields (H_{0}) values consistent with late–time observations and negative value of deceleration parameter at present indicates ongoing acceleration phase of universe, while the reconstructed jerk and (Om(z)) diagnostics show clear departures from constant–(Lambda ) evolution, indicating effective dark-energy like dynamics sourced by Finslerian anisotropy. The predicted cosmic age is slightly higher than (Lambda )CDM. A model selection analysis based on information criteria shows that the Finsler–Kropina model performs competitively with (Lambda )CDM for the CC+ DESI BAO dataset, whereas the full joint dataset mildly favors (Lambda )CDM due to its lower parameter complexity. This demonstrates that Finsler–Kropina geometry offers a viable anisotropic extension of late–time cosmology.

This study uses the k-nearest neighbor (KNN) algorithm, Pearson correlation coefficient to predict sudden storm commencement (SSC), main, and recovery phases of ten intense storms (occurred during 2012-2018), and solar wind coupling with Earth’s magnetosphere. Probability distribution functions (pdfs) for solar wind interplanetary magnetic field (IMF), its Bz component and solar wind speed are also studied. IMF-Bz pdfs included single peak with and without bumps in front and on tail, double peak, and triple peak but highest positive correlation coefficients for double peak dominated those for triple peak distributions. Similar results are found for IMF pdfs. Contrarily, highest positive correlation coefficient occurred for single peak solar wind probability distribution. It is also found that storm phase prediction accuracy reduced when number of nearest neighbors is increased. The accuracy of prediction changed by replacing elements of data vectors. The highest accuracy occurred for data vectors including SYMH index and Bz component of an interplanetary magnetic field. The findings of this study can play a critical role in future space weather.

We present a singularity-free relativistic interior solution for constructing stable quark stellar models in the framework of a linear (f(Q)) gravity ((f(Q) = alpha Q + phi )) satisfying the pseudo-spheroidal geometry. The physical features and the stability of the stellar model is explored with strange star (SS) candidate EXO 1745-248 ((M = 1.7, M_{odot }) and (R = 9, km)). The Durgapal-Banerjee transformation is employed to obtain the relativistic interior solution using the MIT Bag model equation of state (EoS): (P = frac{1}{3}(rho - 4 mathcal{B}_{g})). For a linear form of (f(Q)) gravity, we obtain the exterior vacuum solution, which reduces to the Schwarzschild-de Sitter (SdS) solution with the cosmological constant term, (Lambda = frac{phi }{2alpha }). The stellar model is analyzed for the different values of the spheroidicity parameter ((mu )). The value of (alpha ) is constrained using a viable physical limit on the Bag parameter ((mathcal{B}_{g} in [57.55,95.11],MeV,fm^{-3})). The constraints on Mass-Radius relation indicates that physically acceptable SS models are permitted for (mu geq 7). The contribution of (mu ) to the energy density, pressure profiles, and other physical features is studied for the SS candidate EXO 1745-248. The stability of the stellar model obtained here is also analyzed through causality condition, adiabatic index and other stability criteria. We also investigate the stellar model for other SS candidates to test its viability. The relativistic interior solution obtained here can be used to construct viable and physically acceptable strange star models with very high compactness ratio in the framework of linear (f(Q)) gravity.

This manuscript investigates the impact of key dust evolution parameters—disc viscosity, fragmentation velocity, and the initial gas disc critical radius—on dust retention and trapping in protoplanetary discs. Using models with and without pressure bumps, combined with radiative transfer simulations, images of the dust continuum emission at (sub-)millimeter wavelengths, their fluxes and observed disc sizes are presented. For discs without pressure bumps (smooth discs), significant dust mass can only be retained over Myr timescales when dust fragmentation velocities are low ((v_{mathrm{frag}}=1) m s⁻¹) and with viscosity values of (alpha =10^{-3}). For such a combination of fragmentation velocity and viscosity the synthetic images show a bright inner emission follow by a shallow emission with potential gaps if they are present in the gas profile as well. At higher fragmentation velocities ((v_{mathrm{frag}}=5)–10 m s⁻¹), most dust is lost due to radial drift at million-year timescales unless pressure traps are present, in which case dust masses can increase by orders of magnitude and structures are observed in synthetic images. The viscosity parameter strongly shapes observable features, with low (alpha ) producing sharper, potentially asymmetric inner wall cavities in inclined discs due to optically thick emission. High (alpha ) favors the appearance of shoulders around the predominant rings that dust trapping produces. However, distinguishing between different fragmentation velocities observationally remains challenging. The inferred dust disc sizes from synthetic observations do not always correspond directly to dust model sizes or to the location of pressure bumps. Finally, we discuss implications for pebble fluxes and the delivery of volatiles to the inner disc. These results emphasize the strong degeneracies among dust evolution parameters and highlight the need for multi-wavelength, high-resolution observations to disentangle the processes shaping the formation of planets and planetary embryos in protoplanetary discs.

The functional forms of galactic rotation curves provide a fundamental test for models of gravity and dark matter. In this work, we conduct a rigorous statistical comparison of five distinct models against the complete sample of 175 galaxies from the SPARC database. The models under consideration are: (1) a one-parameter empirical law, physically constrained by each galaxy’s measured flat disc rotation velocity ((V_{text{flat}})); (2) a classical two-parameter Freeman disk; (3) a three-parameter Navarro-Frenk-White (NFW) dark matter halo plus baryons model; (4) a one-parameter Modified Newtonian Dynamics (MOND) model; and (5) a two-parameter Bosma/Dark Matter Disk model. We employ a Bayesian framework with Markov Chain Monte Carlo (MCMC) for parameter estimation, and use the Akaike Information Criterion (AICc) to assess the goodness-of-fit and statistical parsimony of the best-fit models. Our results reveal a decisive preference for the constrained one-parameter empirical model. It is selected as the best descriptor for a clear majority of the sample (60.6%) and, critically, also achieves the best median goodness-of-fit, with a reduced chi-squared of (chi ^{2}_{nu } = 0.41). In contrast, the standard NFW framework is preferred in only 12.6% of cases, while the MOND and Freeman disk models are selected as optimal for just 10.3% and 9.1%, respectively. The Bosma model, despite linking dynamics to the gas distribution, is preferred in only 7.4% of cases. The pronounced statistical and descriptive success of this simple, physically-anchored law over more complex, established theories suggests that its functional form represents a fundamental and highly efficient organizing principle in the dynamics of disk galaxies.

Kepler’s equation is fundamental to celestial mechanics, establishing the link between time and the geometric position of a body in an elliptical orbit. This paper introduces a practical and efficient analytical-numerical method for solving this transcendental equation, offering a robust alternative to classical iterative schemes and infinite series expansions. By employing a tangent half-angle transformation, we map the problem into a domain where the relationship between anomalies is effectively modeled by a polynomial scaling of the transformed variable. The core of the method is a cubic polynomial function, dependent on eccentricity, whose coefficients are determined via a global data-driven optimization rather than local Taylor series. The resulting closed-form formula achieves a mean absolute error on the order of (10^{-15}) radians, limited only by machine precision and demonstrates a computational speedup of two orders of magnitude compared to standard Newton-Raphson solvers and Bessel series methods (Philcox). This work provides a constant-time, high-precision solution well-suited for large-scale N-body simulations and real-time orbit propagation.

Evolved late-type stars are frequently identified as photometric and spectroscopic variables, such as Mira-type or semi-regular variable objects. These stars can also be polarimetrically variable, an indicator of non-spherical geometry for spatially unresolved sources. Departures from symmetry can arise in a number of ways, such as the presence of a binary companion (e.g., multiple illumination sources for scattered light), brightness variations in the stellar atmosphere (e.g., large convective cells), or aspherical circumstellar envelopes (e.g., disks or aspherical stellar winds). Common polarigenic opacities for cool stars include Rayleigh scattering and dust scattering. The classic wavelength dependence of (lambda ^{-4}) for Rayleigh single scattering is generally straightforward; however, that signature can be confounded by interstellar polarization (ISP). We explore strategies for interpreting polarimetric observations when the interstellar polarization (ISP) cannot be removed. We introduce a “hybrid” spectrum that includes both Rayleigh polarization for a stellar contribution and the Serkowski Law for an interstellar contribution. We find the polarization spectral slope can be more shallow than expected from Rayleigh scattering alone. For stellar variability, shorter wavelengths give higher amplitude changes when Rayleigh scattering dominates the interstellar signal. Quite anomalous slopes can occur over limited wavelength intervals if the stellar and interstellar position angles differ by (90^{circ }). Results of the models are discussed in the context of photopolarimetry methods, and an application is considered in terms of variable polarization from the carbon star, R Scl.

Transcritical and saddle-node bifurcation behaviors of nonlinear ion-acoustic wave (IAW) characteristics are examined in a five-component plasma system in the Venusian upper ionosphere at an altitude of 1000-2000 km. The plasma model comprises (H^{+}), (O^{+}) ions, solar wind protons (sp), along with Maxwellian distributed planetary electrons ((e)) and solar wind electrons (se). The governing model equations are transformed into an ordinary differential equation (ODE) using a non-perturbative approach. A planar dynamical system is then derived by applying the theory of phase plane analysis. Various possible phase portraits are constructed to explore the associated nonlinear wave phenomena. The effects of plasma parameters such as (rho ), (omega ), (zeta ) (unperturbed number density ratios), (sigma _{se}) (the temperature ratio), and (lambda ) (the travelling wave speed) on nonlinear wave features are systematically investigated. Specifically, the influences of these parameters on the features of ion-acoustic solitary waves (IASWs) and nonlinear periodic ion-acoustic waves (NPIAWs) are analyzed. It is observed that a decrease in (rho ) enhances amplitude with minimal change in width of the IASW. It is also observed that increasing (omega ), (zeta ), and (sigma _{se}) results in a decrease in amplitude while having a negligible effect on width of the IASW. Additionally, it is observed that a decrease in (lambda ) leads to a reduction in amplitude along with a noticeable broadening of the IASW. It is also observed that increasing (rho ), (omega ), (zeta ), and (sigma _{se}) reduces amplitude and slightly narrows the width of the NPIAW. It is further observed that an increase in (lambda ) significantly increases both amplitude and width of the NPIAW. Vector field diagrams are generated for various values of the control parameter (lambda ), and the corresponding bifurcation curve is plotted. Based on the variation in (lambda ), a combination of transcritical and saddle-node bifurcations is observed in the Venusian upper ionosphere. These findings contribute to a deeper understanding of the bifurcation features of IAWs in the Venusian ionospheric environment.

We present the results of photometric analysis of WZ Sge type dwarf nova TCP J20171288+1156589. This object exhibited an outburst with a large amplitude of (>7.9) magnitudes and was observed for over a month. The photometric evolution of the superoutburst was atypical for WZ Sge-type dwarf novae. Periodogram analysis reveals early superhumps with the most probable period of (0.0611pm 0.0001) days during the initial decline. After a plateau phase of approximately 11 days, ordinary superhumps (likely stage B) emerged with a period of (0.0616pm 0.0001) days, corresponding to a superhump excess of (epsilon =0.008) correspondingly. This delay in the onset of ordinary superhumps is an unusual feature among WZ Sge stars. We evaluated the main parameters of the system: mass ratio (q=M_{RD}/M_{WD}=0.06pm 0.005), yielding component masses of (M_{WD}sim 1.0pm 0.15M_{odot }) for the white dwarf and (M_{RD}=0.06pm 0.01M_{odot }) for the donor. The estimated distance to the system is (sim 850) pc, and the binary separation is (a=0.67pm 0.03R_{odot }).