Astrophysics最新文献

We examine bouncing cosmology in the anisotropic Bianchi type-III framework within Brans-Dicke gravity, incorporating Kaniadakis holographic dark energy with Hubble and Granda-Oliveros radii as infrared cutoff. We reconstruct bouncing model through correspondence scheme utilizing power-law form of the scalar field in terms of average scale factor. The natural anisotropy in Bianchi type-III model modifies expansion dynamics, offering a broader perspective on early-universe evolution beyond standard isotropic models. We analyze key cosmological parameters, including deceleration, jerk, equation of state ω_de , energy conditions, squared sound speed ({upsilon }_{s}^{2}) and ({{omega }_{de}-omega }_{de}{prime}) plane. Models are exhibiting oscillatory transitions across the phantom divide and evolves smoothly toward ω_de at late times. The stability analysis based on the squared sound speed ({upsilon }_{s}^{2}) reveals that models remain dynamically stable over most of the cosmic history and admit instabilities near the bounce. A dynamical phase-space study in the ({{omega }_{de}-omega }_{de}{prime}) plane shows that both models evolve predominantly in the thawing region, implying an asymptotic approach to a cosmological constant. The energy condition analysis further confirms that the violation of the null and strong energy conditions is a necessary feature for the realization of the bounce.

Based on TESS data, starspot activity of stars in five selected moving groups, associations, and clusters with ages from 10 to 425 Myr was analyzed. Rotation periods P, spottedness S, and spot areas A_spot were determined for 704 analyzed objects. From the studied clusters, moving groups, and stellar associations, evidence was found for the temporal evolution of stellar activity. It is shown that the mean level of spottedness in older stellar groups is lower than that in younger ones. Variations in the spottedness of coeval objects as a function of their effective temperature are quantitatively estimated and presented. The estimates of spottedness for solar-type stars of different ages (10–790 Myr) are compared with the spottedness of the Sun.

In this study, attention is drawn to some observable manifestations of the existence of two separate regions with different temporal development during powerful flares on dMe stars and on the Sun. I propose a theoretical interpretation of the origin of the white-light continuum in powerful stellar flares with classical light curves and discuss it in the context of observations of the white-light flares of the first type on the Sun.

This study examines the rotational characteristics of asteroids through statistical modeling of the diameter- period relationship. A statistical evaluation of the diameter-period relationship was conducted using a dataset of 34326 asteroids. Clustering identified three main groups, including a dense cluster below the spin barrier, a population of small, fast-rotating asteroids, and a more diffuse group. Geometric and density-based analyses showed that the densest region consists of objects with diameters from 3 to 10 km and rotation periods between 3 and 9 hours, some of which extend beyond the spin barrier. Polynomial modeling demonstrated that a third-degree fit provides the most stable representation of the overall trend without overfitting. Additionally, an empirical lower boundary was identified and proposed, below which no asteroid was found in either the main sample or the selected targets.

In this paper, we employ the Variable Phase Approach (VPA) to obtain the scattering phase shifts δ (E, r) , amplitude function A (r), and radial wavefunction u(r) for various channels involved in the astrophysical reaction ⁷Be(p ,γ ) ⁸B. Using the extracted phase shifts, we compute the total and partial cross sections. It is observed that the peaks in the partial cross section correspond to resonant states in the compound nucleus ⁸B, which also manifest as enhancements in the astrophysical S-factor. These resonances significantly increase the reaction probability at certain energies, particularly in the lowenergy regime relevant to stellar nucleosynthesis. The VPA thus serves as a reliable and efficient method for calculating scattering phase shifts and, in turn, extracting the resonance energies of different partial waves. These resonance energies can provide valuable insight into the energy region where the astrophysical S-factor is likely to peak.

The paper addresses the problem of determining the degree of starspot coverage of solar-type stars producing superflares, using a method previously developed by the author to estimate the spottedness of flaring stars based on the chronology of recorded flares. The method involves determining a periodic function of flare rate using statistical analysis of time series. The latter are interpreted as a Poisson process with a cyclic parameter associated with the stellar rotation period. Transformation of this function into the von Mises probability density function of circular distribution shifts the perspective from flare frequency to the angular distribution of starspots and determining the effective surface area covered by spots. Nine of the most active solar-type stars from the catalog of Okamoto et al. were investigated. For these stars, rotation periods were calculated using flare chronology, concentration parameters of the flare distribution were determined, and angular distributions of starspot coverage were obtained. The estimated degrees of spottedness range from 1–4% for minimally spotted hemispheres to up to 10% for maximally spotted hemispheres, which significantly exceeds the corresponding values for the Sun. Comparison with the results of Okamoto et al. demonstrates a high degree of agreement, with a correlation coefficient r = 0.896. The developed approach enables determining stellar spottedness based solely on time series of flare activity without the use of high-resolution photometric or spectroscopic data, making it a valuable tool for statistical studies of magnetic activity in solar-type stars exhibiting superflares.

This study investigates the internal structure of compact stars models using the Chaplygin equation of state, a notable candidate for describing exotic matter due to its ability to manifest dark energy through an inverse pressure-density relationship. By integrating this equation of state into the framework of general relativity, we derive solutions that describe stable and physically realistic stellar configurations. The spacetime geometry within the stellar interior is governed by the Buchdahl metric potential, facilitating the construction of analytic models applicable to observed compact objects such as PSRJ1903 + 327, CenX - 3, and VelaX - 1, with respective masses of 1.667 M_⊙ , 1.49 M_⊙ , and 1.77 M_⊙ , and corresponding radii of 9.438 km, 9.178 km, and 9.56 km. To visualize the behavior of thermodynamic variables, two-dimensional contour plots are employed to illustrate the spatial variation of matter density and radial pressure, revealing centrally peaked distributions that decrease smoothly toward the boundary-consistent with expected stellar behavior. The model's validity is further examined using standard physical checks, including the satisfaction of energy conditions, causality constraints, and dynamical stability via the adiabatic index. The results support the Chaplygin gas as a compelling equation of state for describing compact astrophysical bodies and demonstrate the effectiveness of combining analytic methods with advanced graphical analysis in modeling relativistic stars.

For many years, detailed observational and statistical study of the chemically peculiar stars showed that the presence of heavy radioactive chemical elements overabundances in their atmospheres are not well understood. We try to explain the overabundance of a few of them by the explosion of the possible supernovae in binary or multiple stellar system, i.e. to search for a chemically peculiar star and pulsar pair by traceback motion study in the Galaxy. We analyzed trajectories of 529 chemically peculiar stars of our sample and 28 pulsars from ATNF catalogue, which ages do not exceed 100 Myr, and obtained several possible candidate pairs (CP star plus pulsar), which may have been at the same place at the same time. Moreover, our traceback study of them with the young stellar clusters (Hunt and Reffert, 2023) led to the identification of several, possibly, parental stellar groups. Furthermore, more detailed studies are needed to estimate the ages of chemically peculiar stars and detect their locations of formation, as well as use statistical methods to assess whether the possible supernova ejection is the result of coincidence or not. Obviously, modeling of the best chemically peculiar star-pulsar pairs will also allow us to explain the processes occurring in these stars.