Astrophysics and Space Science最新文献

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.

The well-observed type IIP SN 2024bch with the short plateau is shown to be an outcome of the red supergiant explosion with the presupernova mass of (14-15) (M_{odot }), the explosion energy of (2times 10^{51}) erg, and presupernova radius of 1250 (R_{odot }). The early gamma-ray escape demonstrated by the radioactive tail is due to the large ⁵⁶Ni extension up to 7400 km s⁻¹. The early-time spectral evolution indicates the presence of the circumstellar dense confined envelope with the mass of (0.003-0.006) (M_{odot }) within (6times 10^{14}) cm. The deceleration of the outermost ejecta implies the wind with the mass-loss rate of ≈ 6(times 10^{-4}) (M_{odot }) yr⁻¹. The inferred mass-loss rate is by one-two order larger compared to most of type IIP supernovae, but comparable to the wind of type IIL SN 1998S. The asymmetry of the broad H(alpha ) component on day 144 powered by the circumstellar interaction is the outcome of the Thomson scattering and absorption in the Paschen continuum in the unshocked ejecta.

We present the rotation curves of seven dwarf galaxies from the Local Volume Hi Survey (LVHIS) to investigate their Hi gas kinematics and mass distribution. The LVHIS Hi data cubes, with a spatial resolution of 40–50″ and a spectral resolution of (sim 4~mathrm{km},mathrm{s}^{-1}), allow for a detailed analysis of gas kinematics and the relative contributions of baryons and dark matter. Using a Bayesian–based profile decomposition method, we identify kinematic complexities in the gas, particularly in the inner regions, which may arise from observational beam smearing or stellar feedback processes. Through 2D tilted–ring analysis, we derive rotation curves that exhibit solid-body rotation in the inner regions, transitioning to flat or gradually rising curves in the outer parts. An asymmetric drift correction applied to the rotation curves shows minimal impact, attributed to the low Hi velocity dispersion and gas surface densities in the galaxies’ outer regions. Disk—halo decomposition using the Cold Dark Matter NFW and pseudo-isothermal halo models is limited by the coarse spatial resolution of the LVHIS Hi data and the absence of high–quality optical and infrared observations, which hinders a clear distinction between the models. Nonetheless, this study complements our understanding of the overall rotation curve shapes and Hi gas kinematics of galaxies in the local Universe.

Convection in the innermost shells of massive stars plays an important role in initiating core-collapse supernovae. When these convective motions reach the supernova shock, they create extra turbulence, which helps energize the explosion. In our earlier work, we studied the effect of rotation on the hydrodynamic evolution of convective vortices in collapsing stars. This study focuses on how rotation influences the entropy perturbations, which naturally form in turbulent convection. As these perturbations are carried inward with the collapsing star, they generate both vorticity and sound waves. Using linear perturbation theory, we model entropy waves as small disturbances on top of a steady background flow. Our results show that stellar rotation has little effect on the evolution of entropy perturbations during collapse, prior to encountering the supernova shock. This outcome is consistent with our earlier findings on the limited influence of rotation in the accretion of convective eddies.

A valuable probe for examining relativistic gravity, star stricture, and the dynamical development of near binary systems is the apsidal motion of a non-synchronous binary pulsar. In this study, we examine the combined effects of tidal interaction, star oblateness, and general relativity on the apsidal motion of three binary pulsars: J0621+1002, J0737-3039A/B, and 1913+16. Tidal effects and their role in orbital and spin evolution were described by numerical integrations using Zahn’s tidal equations (Astron. Astrophys. 57:383–394, 1977, Astron. Astrophys. 220:112–116, 1989). We calculated the orbital circularization and tidal synchronization timescales for each system. The simulated results show a clear trends of decreasing of both the semi-axis and eccentricity, while increasing the spin rate. In addition, the tidal effects play only a minor role in orbital decay compared with energy loss due to gravitational wave emission. Both the obtained apsidal motion constants [(ksimeq 0.1)] and the derived tidal friction periods, which vary from a few hours to several days, correspond well with theoretical estimates. This is demonstrated in the compact system PSR1913+16, where gravity radiation causes the orbital period to decrease by approximately 76.5 μs/yr. While the wider system J0621+1002 displays minor orbital change over timescale exceeding 10¹⁰ yrs, the double pulsar J0737-3039A/B exhibits faster orbital evolution, with synchronization occurring in about 8.4(times 10{^{3}}) yrs. The results demonstrate the significance of relativistic effects in neutron star binaries and the necessity of incorporating gravitational wave terms in long-term orbital evolution.

This research examines the variations of the relativistic electron flux (REF) with E > 0.8 MeV and > 2 MeV at geostationary orbit (GEO) and in outer radiation belts (ORB) selected events of high-intensity long-duration continuous AE activity (HILDCAA) during 2015 to 2017. We have utilized the solar wind plasma data and geomagnetic storm indices, source and seed electron flux, chorus wave spectrograms, and ULF indices. We found strong linear correlation between the maximum of AE (AL) and max REF, and between the peaks solar wind speed (V_max) and max Log REF. The E > 0.8 MeV REF increases before the E > 2.0 MeV REF. Then they concurrently changed with the increasing rate of the E > 2.0 MeV REF is faster than that of the E > 0.8 MeV REF. The Alfvénicity (i.e., the extent to which fluctuations follow the Alfvén wave characteristics), with the southward interplanetary magnetic field of the Alfvén waves is essential for the substorm occurrence. The REF enhancements at GEO are categorized into nominal, high, and very high levels. The conditions of very high REF are 1690 ≤ AE_max ≤ 2178 nT and 742 ≤ V_max ≤ 860 km/s. The large ULF waves are found in the high and very high REF and often appear in the high-Alfvénic events. The Chorus wave activity persists in conjunction with the injection of source and seed electrons. Nominal REF occurs in the moderate ULF and the highest REF was around L = 4–5 without loss of REF in the ORB. The prominent Chorus and ULF waves recurrently appear in some consecutive HILDCAA events that sequentially and synergistically enhance the REF to very high levels. Near L = 4, the REF was locally enhanced by Chorus wave throughout the HILDCAA and recovery phase. The consecutive recurrent Chorus relates to the loss of REF in the range of L = 4–6. Events with no clear Chorus in the ORB can possess high and very high REF at GEO and the loss of REF is at L = 4–5 during the Equinoctial times. Moreover, REF shows semiannual variation, with maxima fluxes near the equinoxes.

The goal of this paper is to obtain an approximate solution of the restricted three-body problem in the case of small perturbations in the vicinity of, but not in exact resonance. In this paper, we study the restricted three-body problem known as planetary type (i.e., when the eccentricity of the test particle is small). A method of linearizing the equation of motion close to (but not in) resonance is proposed under the assumption of small perturbations. In other words, we study orbits when the resonant argument circles the resonance. In the practically interesting case of resonant perturbations we can restrict our study to a perturbation with a single frequency with the largest amplitude, and reduce the problem to the Mathieu equation. The model qualitatively describes the behavior of the perturbation in the vicinity of the resonance. It can be used to estimate the exact position of the resonance and the boundaries between neighboring resonances.