Astrophysics and Space Science最新文献

Understanding the physics of particle acceleration at shocks is a long-standing problem in space science and astrophysics. Because particles are energized across the shock upstream and downstream through Diffusive Shock Acceleration (DSA), the characteristics of upstream and downstream plasma waves involved in wave-particle interactions have been extensively examined. While many studies have focused on self-excited plasma instabilities due to shock-reflected and accelerated particles, the roles of pre-existing turbulence in astrophysical environments could be substantial for wave-particle interactions near the shock. This work specifically investigates the effects of pre-existing turbulence in the shock upstream on DSA efficiency. The normalization and slope of turbulent spectra are used as parameters to determine the characteristics of pre-existing turbulence. Since pre-existing turbulence can confine particles upstream and regulate their efficient acceleration through DSA across the shock, the DSA efficiency decreases as the strength of turbulence increases. Furthermore, the effects of pre-existing turbulence become less significant in plasma systems with higher plasma beta, as diffusion mediated by both self-excited waves and pre-existing turbulence becomes less efficient as plasma beta increases. The modeling presented in this work could be generally applicable to shocks propagating through turbulent regions.

The Habitable Worlds Observatory (HWO) will enable a transformative leap in the direct imaging and characterization of Earth-like exoplanets. For this, NASA is focusing on early investment in technology development prior to mission definition and actively seeking international partnerships earlier than for previous missions. The “R&D for Space-Based HCI in Europe” workshop, held in March 2024 at Paris Observatory, convened leading experts in high-contrast imaging (HCI) to discuss European expertise and explore potential strategies for European contributions to HWO. This paper synthesizes the discussions and outcomes of the workshop, highlighting Europe’s critical contributions to past and current HCI efforts, the synergies between ground- and space-based technologies, and the importance of laboratory testbeds and collaborative funding mechanisms. Key conclusions include the need for Europe to invest in technology development for areas such as deformable mirrors and advanced detectors, and establish or enhance laboratory facilities for system-level testing. Putting emphasis on the urgency of aligning with the timeline of HWO, the participants called on an open affirmation by the European Space Agency (ESA) that a European contribution to HWO is clearly anticipated, to signal national agencies and unlock funding opportunities at the national level. Based on the expertise demonstrated through R&D, Europe is poised to play a pivotal role in advancing global HCI capabilities, contributing to the characterization of temperate exoplanets and fostering innovation across domains.

We investigate the period changes of 13 short-period Type II Cepheids using the O-C method over a century-long data baseline. The O-C diagrams for these stars exhibit a parabolic trend, indicating both increasing and decreasing period changes over time. These observed period changes are consistent with recent theoretical models based on horizontal branch evolutionary models for short-period BL Her stars. The pulsation stability test proposed by Lombard and Koen confirms that the period changes are significant, indicating evolutionary shifts. We identify seven BL Her stars with decreasing periods, expanding the existing sample size of short-period Type II Cepheids. This contributes to a deeper understanding of stellar evolution and the processes governing low-mass stars.

We study the existence and stability of equilibria in the regular n-gon restricted ((n+1))-body problem with logarithm potential. We determine two classes of equilibria: “infinitesimal-Eulerian” situated along lines joining the n-gon centre with a vertex (i.e. along the radii), and “infinitesimal-Lagrangian” situated on the perpendicular bisectors of the n-gon sides. The infinitesimal-Eulerian equilibria are all positioned outside the primaries n-gon and are unstable. The infinitesimal-Lagrangian equilibria appear in two families: an unstable family in the interior of the primaries’ polygon, and a linearly stable family in the exterior. We also prove the existence of an equilibrium at the centre of the polygon that is unstable.

One of the current theories about the formation of a planetary system conjectures that traveling waves within a primordial interstellar gas cloud might have led, eventually, to the formation of the planets. As an initial step in this process embedded solid particles within a traveling wave may commence self-gravitational accumulation at the wave crests, where the pressure and density are highest, so possibly leading to the formation of cometary nuclei. To test the validity of this conjecture we present in this paper a prototype model for the evolution of systems of self gravitating particles. This model is applied to linear and circular traveling waves and ensembles of particles in a disk. We show that under proper conditions these systems might undergo a bifurcation or “self organization” which leads to the formation of cometary nuclei.

We compute the families of periodic orbits for the retrograde coorbital (1/-1) resonance at Neptune to Sun mass ratio, in the planar circular restricted three-body problem (CR3BP), and their bifurcations into three-dimensional families. We show that when a small body slowly approaches the planet due to the action of a drag force, or when Neptune slowly migrates outward, capture of nearly coplanar retrograde orbits in the coorbital resonance follows the families of periodic orbits and occurs with (100%) probability for Trans Neptunian Objects (TNOs) with initial nearly circular orbits. We also present statistics of capture in resonance, due to Neptune’s migration, of TNOs with eccentric nearly coplanar retrograde orbits.

Accurate identification of solar radio bursts (SRBs) is essential for advancing research in solar physics and predicting space weather. However, the majority of current studies mainly concentrate on detecting whether SRBs are present or absent, often focusing on only one particular type of burst. Moreover, the neural network models used for SRB detection are typically complex, involving a large number of parameters, which results in slower processing speeds. This study establishes a dataset encompassing Type II, Type III, Type IIIs, Type IV, and Type V SRBs collected from e-CALLISTO, including 8,752 SRB spectrum images and achieving annotations for 10,822 SRBs. We propose a multi-category SRB detection model based on task-aligned one-stage object detection (TOOD). TOOD can solve the problem of inconsistent predictions in classification and localization tasks, and it improves the detection recall rate. This model aligns classification and localization tasks and optimizes the neck network by incorporating a channel attention mechanism. This model achieves higher recall and accuracy with fewer parameters. This model can accurately detect five types of SBRs. The experimental results show that the model achieved an accuracy of 79.9% (AP50) and a recall rate of 95.1% on the SBRs dataset. A higher recall rate than other models means fewer SRBs are missed in automatic detection. The model we propose has the potential to make a substantial impact on solar physics research and space weather studies. Additionally, the findings in this paper could provide valuable insights for processing other small-sample astronomical, datasets. The source code and data is available at https://github.com/onewangqianqian/MobileNetVitv2-TOOD.git.

RR Lyrae stars are important distance indicators. They are usually present in globular clusters where they were first discovered. The study of their properties and distribution in our Galaxy and in external galaxies constitutes a modern field of astrophysical research. The aim of this paper is checking the possibility that the observed distribution of RR Lyrae stars in the Galactic bulge derives from orbitally decayed globular clusters (GCs). To reach the aim of the paper I made use of the comparison of observational data of RR Lyrae in the Galactic bulge with the distribution of GCs in the Milky Way (MW) as coming from theoretical models under a set of assumptions. I obtain the expected numbers and distributions of RR Lyrae in the Galactic bulge as coming from an initial population of globular clusters at varying some characteristic parameters of the GC population and compare to observational data. The actual abundance of RR Lyrae in the Galactic bulge and their radial distribution are, likely, still too uncertain to provide a straight comparison with theoretical models. Despite this, it can be stated that a significant fraction of the ‘foreground’ RR Lyrae present in the MW originate from orbitally evolved and dissolved GCs.

As compact relativistic objects, white dwarfs are in different classes than neutron stars. Because white dwarfs are comparatively less compact than neutron stars are, the equation of state of a white dwarf is comparatively more certain. In this work, we investigated the basic properties of nonrotating white dwarfs composed of charged perfect fluid in the context of 4D Einstein-Gauss-Bonnet gravity. For example, we derived the mass, radius, energy density, pressure, charge distribution, and electric field of white dwarfs and demonstrated their dependency on the Gauss-Bonnet coupling constant (alpha ) in terms of the effect of charge. The structural solutions of white dwarfs are obtained by adopting Chandrasekhar’s equation of state and a significant relationship between charged density and energy density. In this context, we solve the TOV equation with the addition of the charge profile numerically by considering appropriate boundary conditions at the center of the star. By adjusting different parameters, we present a detailed graphical discussion of several characteristics of white dwarfs. We emphasize the mass-radius relationship of our proposed white dwarfs and compare the results with the Chandrasekhar mass limit for viable white dwarf structures. Moreover, the nature of the sound speed profile and adiabatic index in the internal structure of white dwarfs are discussed. As a result, we obtain a physically viable charged white dwarf structure with a mass near the Chandrasekhar mass limit in the context of the Einstein-Gauss-Bonnet gravity.

Observations of stars other than the Sun are sensitive to oscillations of only low degree. Many are high-order acoustic modes. Acoustic frequencies of main-sequence stars, for example, satisfy a well-known pattern, which some astronomers have adopted even for red-giant stars. That is not wise, because the internal structures of these stars can be quite different from those on the Main Sequence, which is populated by stars whose structure is regular. Here I report on pondering this matter, and point out two fundamental deviations from the commonly adopted relation. There are aspects of the regular relation that are connected in a simple way to gross properties of the star, such as the dependence of the eigenfrequencies on the linear combination (n+textstyle {frac{1}{2}}l) of the order (n) and degree (l), which is characteristic of a regular spherical acoustic cavity. That is not a feature of red-giant frequencies, because, as experienced by the waves, red-giant stars appear to have (phantom) singular centres, which substantially modify the propagation of waves. That requires a generalization of the eigenfrequency relation, which I present here. When fitted to the observed frequencies of the Sun, the outcome is consistent with the Sun being round, with no singularity in the core. That is hardly novel, but at least it provides some assurance that our understanding of stellar acoustic wave dynamics is on a sound footing.