Astrophysics and Space Science最新文献

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 }).

To address the challenges of low signal-to-noise ratio and poor localization in detecting faint celestial objects from ground-based optical images, we propose CRFusion-Det, a plug-and-play probabilistic detection head. It introduces innovations at both the feature representation and inference levels. First, dilated convolutions and the CBAM attention module are integrated into the heatmap and width-height regression branches to enhance multi-scale contextual perception. Second, for offset estimation, the keypoint coordinate regression is innovatively reformulated as a probability distribution modeling problem. This is achieved via a learnable Prospect/Background Probability Estimation Module (PBPEM) and a Spatial-Appearance message Transmission Module (SATM), which explicitly capture inter-target geometric constraints and appearance consistency. A mean-field iterative algorithm is employed for structured inference, enabling progressive distribution refinement and sub-pixel localization. Extensive experiments on real-world datasets demonstrate CRFusion-Det’s effectiveness and generalization. When integrated into five different baseline networks, it consistently improved the recall by 1.68%–5.24% and reduced the normalized mean error to as low as 0.05 (0.73 pixels). The proposed CRFusion-Det significantly enhances the detection and localization accuracy of baseline models for faint targets, validating its superiority as a solution for astronomical image processing.

Observational evidence has continued to mount that a significant fraction of rapidly rotating early-B type stars are products of binary mass transfer. However, very few mid- and late-type B stars with rapid rotation have been demonstrated to be post-interaction products, despite a growing sample of SB1 binaries among stars within this range of spectral types. By considering the currently available information over the entire range of rapidly rotating B-type binaries, we argue that a significant fraction of the mid- and late-type rapid rotators found in binaries are also likely the result of past mass transfer episodes. The observed properties of this sample are compared to the predictions from the Binary Population and Spectral Synthesis code (BPASS), with attention given to the expected evolutionary pathways of stripped stars and the stellar and binary properties of both components of post-interaction systems across a range of initial conditions. Prospects for directly detecting and characterizing the stripped cores of the previous mass donors in such systems are described, and the implications for the role of binary interaction in causing rapid rotation are discussed. An accurate description of prevalence of binary interaction, the physics of mass transfer, and the post-interaction configuration of systems over a range of initial conditions has far-reaching implications including double-degenerate binaries and their eventual mergers, the output of ionizing UV flux of stellar populations, and the supernova explosions that can arise from stripped or rapidly-rotating progenitors.

In this study, we conduct a comprehensive investigation of magnetospheric ultralow frequency (ULF) Pc5 (2–7 mHz) waves that occurred during the geomagnetic storms of 22 June 2015, 17 March 2015, and 7 September 2017. These events presented a unique opportunity to analyze the characteristics and behavior of ULF waves in the magnetosphere, as they are closely linked to various geophysical phenomena, including magnetospheric dynamics and ionospheric responses. We employ continuous wavelet analyses to investigate the time-frequency characteristics of Pc5 ULF waves. Analysis reveals the presence of Pc5 pulsations during the arrival of interplanetary shocks. Cross-correlation analysis shows that Pc5 pulsations are positively correlated with interplanetary magnetic field (IMF), solar wind speed (Vsw), proton number density (Nsw), and solar wind pressure (Psw). Similarly, the AE index and Polar Cap index also show a positive correlation. These observations indicate that due to a sudden increase in solar wind velocity and proton number density after the interplanetary shock, gradually increasing solar wind dynamic pressure and a sudden compression from the Earth’s dayside magnetosphere, results in ULF Pc5 waves being generated in the magnetosphere.

The variability of the H(alpha ) chromospheric activity of solar-like stars is investigated by using the time-domain data of the LAMOST Medium-Resolution Spectroscopic Survey (MRS). Strict screening conditions are employed to ensure the quality of the selected MRS spectra and the consistency between the H(alpha ) spectra of each stellar source. We use the (R_{mathrm{Halpha }}) index (ratio of the H(alpha ) luminosity to the bolometric luminosity) to measure the H(alpha ) activity intensity of a spectrum, and utilize the median of the (R_{mathrm{Halpha }}) values of multiple observations ((R_{mathrm{Halpha }}^{mathrm{median}})) as the representative activity intensity of a stellar source. The H(alpha ) variability of a stellar source is indicated by the extent of the (R_{mathrm{Halpha }}) fluctuation ((R_{mathrm{Halpha }}^{mathrm{EXT}})) of multiple observations. Our sample shows that the (R_{mathrm{Halpha }}^{mathrm{EXT}}) of solar-like stars is about one order of magnitude smaller than the (R_{mathrm{Halpha }}^{mathrm{median}}). The distribution of (log R_{mathrm{Halpha }}^{mathrm{EXT}}) versus (log R_{mathrm{Halpha }}^{mathrm{median}}) reveals the distinct behaviors between the stellar-source categories with lower ((log R_{mathrm{Halpha }}^{mathrm{median}} < -4.85)) and higher ((log R_{mathrm{Halpha }}^{mathrm{median}} > -4.85)) activity intensity. For the former stellar-source category, the top envelope of the distribution first increases and then decreases with (log R_{mathrm{Halpha }}^{mathrm{median}}); while for the latter category, the top envelope of the distribution is largely along a positive correlation line. In addition, for the stellar sources with lower activity intensity, the large-(log R_{mathrm{Halpha }}^{mathrm{EXT}}) objects near the top envelope of the (log R_{mathrm{Halpha }}^{mathrm{EXT}}) versus (log R_{mathrm{Halpha }}^{mathrm{median}}) distribution tend to have long-term and regular variations of H(alpha ) activity; while for the stellar sources with higher activity intensity, the H(alpha ) variations are more likely to be random fluctuations.