Astrophysics最新文献

The dM4e dwarf GJ 1243 (KIC 9726699) has been a subject of extensive research due to its unique flare activity and the evolution of spots on its surface. This paper presents the results of a study into the long-term activity cycles of this star, derived from archival photometric time series. Observations from three independent surveys in different photometric filters indicate long-timescale variability in the luminosity of GJ 1243, with four characteristic cycle durations (we will number them from 1 to 4), clustered around the following P_cycl values (1 to 3): 1.5 years, 2.6 years, and 6.3 years, respectively, and near P_cycl (4) of the order of 12.3–12.6 years. A detailed analysis of the GJ 1243 data on the logarithmic P_cycl/P_rot versus 1/P_rot diagram and comparisons with other M dwarfs reveal a unified relationship for short cycles across the studied stars.

In this paper, we use the distributions of observed γ-ray properties, as well as orientation parameters of a sample of Fermi-LAT AGNs to investigate the hypothesis that γ-NLS1 objects are beamed sources with γ-ray emitting axes inclined at close angles to the line of sight. Based on these parameters we investigate the relationship between γ-NLS1s and other subclasses of γ[-ray emitting jetted AGNs. Results show that γ-NLS1s are more highly beamed than both FSRQs and BL Lacs with mean value of core-dominance parameter R_g ~ 9507. γ-NLS1s and jetted Seyfert galaxies are continuous in distribution of the orientation parameter with average cone angles Φ_m ~ 8° and 44° respectively. Furthermore, the spectral energy distribution of γ-NLS1 is comparable to those of FSRQs and BL Lacs suggestive that γ-NLS1s and blazars form a continuous spectral sequence. There is a significant anti-correlation (r ~ -0.9) between the γ-ray dominance D_g and γ-ray luminosity. There is a strong dependence of D_g on redshift (r ~ -0.7) suggestive that D_g is more sensitive to environmental factors than intrinsic γ-ray luminosity. The results suggest that γ-NLS1s are highly beamed γ-ray sources whose de-beamed counterparts can be found among Seyfert galaxy populations.

We considered the planetary system of TOI-6255, in which an Earth-like planet with an extremely short period of 5.7 hours orbits an M dwarf. Based on archival measurements of TOI-6255 brightness we established rotation-induced light variability and periodic long-term variability of the object. Possible rotation period P of the star falls within the periods of 64–74 days and 78–92 days. The results were compared with those reported in the literature. For two values of logR'_HK (-5.15 and -4.66), corresponding to the peaks of the bimodal distribution of this parameter for low-activity and active M dwarfs, the atmospheric mass loss rates of the planet TOI-6255 b were estimated: 4.9 · 10⁹ g/s for logR'_HK = - 4.66, and 1.1 · 10⁹ g/s for logR'_HK = - 5.15. We determined the promise of TOI-6255 b to become a high priority subject for future research.

A quantitative analysis of the spectra of CQ Tau and UX Ori stars belonging to the family of young irregular variable stars with Algol-like decrease in brightness has been performed. The spectra were obtained at the Nordic Optical Telescope (NOT) observatory at times when the stars were in a bright state. On their basis, the equivalent widths of the photospheric absorption lines, as well as the Hα emission line, are determined. The equivalent width of the latter is used to estimate the gas accretion rate on the stars.

We consider the kinematic distances to nearby galaxies obtained by the Numerical Action Method (NAM) based on the Cosmic-flow-3 survey data. NAM-distances are compared with 418 high-precision distances measured by the Tip of the Red Giant Branch (TRGB) method using the Hubble Space Telescope. We estimated the average difference <D_NAM - D_TRGB > = -0.30 ± 0.08 Mpc and the standard deviation of 1.57 Mpc. Approximately the same difference in the distance scale is obtained in comparison with less accurate distance estimates through the membership of galaxies in known groups or from the Tully-Fisher relation. We conclude that the NAM method provides distance estimates with an accuracy of 20% within the Local Volume, which is valid for ~90% of the sky, except for the regions of the Virgo cluster and the Coma-I group.

We investigate the influence of the helical compactification of spatial dimension on the local properties of the vacuum state for a charged scalar field with general curvature coupling parameter. A general background geometry is considered with rotational symmetry in the subspace with the coordinates appearing in the helical periodicity condition. It is shown that by a coordinate transformation the problem is reduced to the problem with standard quasiperiodicity condition in the same local geometry and with the effective compactification radius determined by the length of the compact dimension and the helicity parameter. As an application of the general procedure we have considered locally de Sitter spacetime with a helical compact dimension. By using the Hadamard function for the Bunch-Davies vacuum state, the vacuum expectation values of the field squared, current density, and energy-momentum tensor are studied. The topological contributions are explicitly separated and their asymptotics are described at early and late stages of cosmological expansion. An important difference, compared to the problem with quasiperiodic conditions, is the appearance of the nonzero off-diagonal component of the energy-momentum tensor and of the component of the current density along the uncompact dimension.

Based on data from the Kepler orbital observatory, this study investigates the most active flare stars, which exhibited 250 or more flares during the Kepler mission period. The main research objectives were: (a) analyzing light curves to identify unique physical characteristics of individual stars; (b) defining the periodic/cyclic flare frequency function (PFFF) of flare stars, associated with axial/orbital rotations; and (c) presenting a novel method for determining starspot coverage using the PFFF and applying this method. The study produced corresponding PFFF values with periodicities close to the star rotation periods. Expected phase distributions of flares were constructed and compared with observed flare distributions for the given rotation period. For all stars examined, this comparison (using the χ² criterion) supports the periodicity of flare frequency. It is hypothesized that the starspot distribution of flare stars can be represented by the von Mises circular distribution, with parameters derived from the respective flare frequency function. Estimates of the starspot coverage for the stars studied were obtained.

The article considers the issue of changes in the total energy of baryonic objects and their systems in the presence of dark energy, whose carrier, by definition, interacts with all baryonic objects. It is emphasized that dark energy was discovered due to such interaction that accelerates the universe’s expansion. Since dark energy (dark energy carrier) is uniformly distributed, the physical consequences of interaction between the dark energy carrier and baryonic matter are considered at all hierarchical levels of baryonic structures. Drawing on the second law of thermodynamics, the author concludes that under the effect of dark energy, the energy of all baryonic systems gradually increases and their stability declines while the virial value becomes positive and continues to grow for any structures considered to be stable. A similar analysis performed for atomic nuclei reveals that over time, nuclear binding energy decreases, nuclear stability declines, and the nuclear mass increases. This effect gives a new perspective on Ambartsumian’s hypothesis about the existence of superdense matter clumps in the nuclei of stars and galaxies and enables its new interpretation.

This paper investigates the thermodynamic properties of vacuum nonsingular black holes. Considering the energy characteristics of the regularity spacetime, we use the modified first law of black hole thermodynamics to calculate the black holes' Hawking temperature, entropy and heat capacity. The obtained temperature is the same as that obtained by the surface gravity and tunneling methods. Also, the entropy is satisfied with the Bekenstein-Hawking area law. Notably, the heat capacity of large-mass black holes diverges, while that of small-mass black holes tends to zero, with a phase transition point existing. Additionally, we consider the quantum gravity effect by using the generalized uncertainty principle to study the quantum corrections of the thermodynamic properties for the vacuum nonsingular black holes. The generalized uncertainty principle introduces a logarithmic correction term to the black hole entropy. Also, the temperature and heat capacity are modified.

We consider the Bianchi type-VI₀ space time with domain walls in the framework of the modified f (R, T) theory of gravitation. To solve the field equations, we assume that the shear scalar σ is proportional to the expansion scalar θ. We also consider the parametrization of the equation of the state parameter of barotropic fluid and discuss the effect on domain walls. It has been observed that the domain wall may behave like dark energy. Some physical parameters are also discussed in detail.