Astrophysics最新文献

In the context of f (R, T) modified gravity theory, we investigate a cosmological model with homogeneous and anisotropic properties, specifically the Locally Rotationally Symmetric (LRS) Bianchi type-I model. By considering Einstein’s field equations in f (R, T) gravity, we solve them with the choice f (R, T) = R + 2f (T), where R represents the Ricci scalar and T denotes the trace of the stress-energy momentum tensor T_ij. In this case, we set f (T ) = -λT, with λ being an arbitrary constant. It is worth noting that the cosmic jerk parameter j is directly proportional to the negative value of the deceleration parameter q, namely j ∝ - q. We analyze the physical and geometrical properties of the models, and also employ the statefinder diagnostic pair to gain insight into the geometrical nature of the model. We also investigate the validity of the generalized second law of thermodynamics (GSLT) on the apparent and event horizons. Our findings reveal that GSLT holds on both the horizons.

Electromagnetic radiation of a relativistic gas or plasma jet in the field of a plane gravitational wave is investigated. The gravitational wave is considered as a weak (linearized) field on flat Minkowski spacetime. It is assumed that the relativistic jet has large regions with uncompensated electric charge. The deformation of these areas under the action of a gravitational wave leads to the appearance of electric currents that generate electromagnetic radiation. The angular distribution of the intensity of this radiation is found. Cases are considered when the jet and the gravitational wave move in the same direction or towards each other.

Knowing rotational and centrifugal distortion constants in conjunction with electric dipole moment for HO₂ radical, we have calculated energies for rotational levels (without fine-structure splitting), and probabilities for radiative transitions between the levels. The radiative transition probabilities in conjunction with the scaled values for rate coefficients for collisional transitions between the levels, the Large Velocity Gradient (LVG) analysis for HO₂ is performed. Two observed lines, 2₀₂-1₀₁ and 4₀₄-3₀₃ of HO2 are found to show MASER action. Seven lines 1₁₀-1₁₁, 2_{1. 1}-2_{1. 2}, 3_{1. 2}-3_{1. 3}, 4_{1. 3}-4_{1. 4}, 5_{1. 4}-5_{1. 5}, 6_{1. 5}-6_{0. 6} and 7_{1. 6}-7_{0. 7} are found to show anomalous absorption and five more lines, 7_{1. 6}-7_{1. 7}, 1_{1. 0}-1_{0. 1}, 2_{2. 1}-3_{1. 2}, 4_{2. 3}-3_{1. 2} and 4_{4. 1}-3_{3. 0} are found to show MASER action. These 14 lines are analyzed here and they may play key role in the identification of HO₂ in a cosmic object.

We present International Ultraviolet Explorer (IUE) observations during the period (1980 - 1994) of the double lined spectroscopic binary BY Dra to show the spectral behavior and physical conditions in its atmosphere. The observations reveal indication of flare activity in their flux values in years (1981-1990-1994) in the chromosphere and transition region of the primary star. Beside the flaring activity the emission lines show a range of variations between high, intermediate and low. There is a relation between the fluxes and rotational phase. The reddening of BY Dra was estimated from 2200 Å absorption feature to be E(B - V) = 0. The average mass loss rate is found to be ~4.9⋅10^-8 M_⨀ yr^-1, the average temperature of the emitting region to be ~9.2⋅10⁴ K, energy of flare to be ~6.2⋅10³⁷ erg. We attributed the spectral variations to a cyclic behavior of the underlying magnetic field and the flaring activity to three component model.

The results of spectroscopic and photometric observations of 14 compact planetary nebulae are presented. Observations were conducted at the V.G. Fesenkov Astrophysical Institute (Kazakhstan) since 1973. The aim of this study is to obtain data on the variability of the studied objects over long time spans. The criterion for determining the nebular excitation class was the intensity of the [OIII] lines normalized to the intensity of Hβ. Analysis of the data collected over 40–50 years revealed significant spectral changes in most of the observed objects, likely associated with an increase in the temperature of the central stars and/or changes in the internal structure of the nebular envelopes.

In this study, we conducted a detailed astrometric, and photometric study of four open clusters (SAI 43, SAI 47, SAI 63, and SAI 113) using data from Gaia DR3. The ASteCA code enabled the identification of the astrometric and photometric parameters. The new centers of these clusters were redetermined and from Radial Density Profile (RDP), the cluster radii, are between 3.13- and 6.6 arcmin for all clusters. The astrophysical parameters are as follows: the number of star members N are 141 (SAI 43), 153 (SAI 47), 198 (SAI 63), and 188 (SAI 113); parallax (ϖ) for SAI 43, SAI 47, SAI 63, and SAI 113 are between 0.275 and 0.506 mas; proper motion parameters (μ_a cosδ, μ_δ) are (0.57, -0.54 mas/yr), (0, -0.34 mas/yr), (-0.24, 0.26 mas/yr), and (-5.61, 2.84 mas/yr) for SAI 43, SAI 47, SAI 63, and SAI 113, respectively. The photometric parameters include the color magnitude diagram (CMD), ages, reddening, and distances. The ages are provided as log (age), and they are between (7.172-8.659); the color excess E(B-V) is 0.476±0.017 mag for SAI 43, 0.375±0.014 mag for SAI 47, 0.510±0.009 mag for SAI 63, and 1.265±0.011 mag for SAI 113, the distance modules of the clusters are between 11.177-13.439 mag, and the distances from the sun to each of the clusters (SAI 43, SAI 47, SAI 63, and SAI 113) are calculated as 4900±100 pc, 2360±30 pc, 1720±20 pc, and 3720±50 pc, respectively.

The sum of C+N+O in red giants presents interest due to its steady nature during stellar evolution of the star, although the abundance of its components, especially C and N, undergoes significant evolutionary changes. It is shown that there is a pronounced correlation between the total log ε(C+N+O) abundances in red giants and their metallicity index [Fe/H]. The linear relationship between log ε (C + N + O) and [Fe/H] indicates an increase in log ε (C+N+O) from 7.0 with [Fe/H] = -2.5 to 9.2 with [Fe/H] = +0.3, i.e., by more than 2 dex. In contrast, the abundance of (C+N+O) relative to Fe decreases by 0.7 dex over the same [Fe/H] interval. It is shown that the ratio between [(C+N+O)/Fe] and [Fe/H] is almost completely determined by the ratio between [O/Fe] and [Fe/H]; hence, it is confirmed that oxygen is the main contributor to C+N+O. Since current models of Galactic evolution explain the observed dependence of [O/Fe] on [Fe/H] reasonably well, they thereby also explain the observed dependence of [(C+N+O)/Fe] on [Fe/H].

An analysis of the blazar sample from the BZCAT catalog reveals that these objects exhibit such special properties, as strong radio emission, optical and radio variability, continuous optical spectra, polarization, and high luminosity, among others. Initially, the catalog included objects with optical variability and strong radio emission, specifically BL Lacertae (BLL) objects and flat-spectrum radio quasars (FSRQ)). Along with the above properties, 48% of blazars produce X-ray emission. This study investigates the X-ray properties and other characteristics of blazars determined through our analyses and calculations.

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.