Astrophysics最新文献

Finding a completely promising theory of gravitation that urges us to go beyond the general theory of relativity. One such approach is an extended class of symmetric teleparallel theory of gravity, namely f (Q, T ) gravity. In this work, we have explored the cosmological background of the flat FLRW universe within the framework of this theory. The cosmic transit phenomenon of the deceleration parameter is studied by employing periodic varying deceleration parameter and obtaining the exact solution of the highly non-linear field equations. The periodic scenario of cosmological models with two different Lagrangian forms of f (Q, T ) is analyzed, where the first form is linear and the second one is non-linear dependent on Q. The dynamical features of both the models, including the periodic behavior of the equation of state parameter are discussed. The self-stability and self-consistency of the derived models are tested by studying energy conditions. Additionally, the geometrical diagnostic validation of the model is also checked.

In this paper we have undertaken the study of systems with both radiating primaries in the frame work of elliptic restricted three body problem where the orbits of the two massive bodies about each other is assumed to be elliptic and the mass of the third body is negligible. In order to determine the problem's solution, we expand the formulation of the iterative expression for the Lie series terms. The impact of the primaries' radiation pressure on the orbit is depicted graphically in the Lie series solution of triangular equilibrium point L₄.

We report the results of our spectroscopic and polarimetric observations of 2° × 2° field around the globule Barnard 5 (B5) belonging to the Perseus cloud complex at the distance d ≈ 300 pc. Using these data, two-dimensional spectral classification was made for about 45 stars. Multi-band polarimetry of about 20 of these stars allowed us to find the parameters (P_max, λ_max) of interstellar polarization. Using the Gaia parallaxes and data from the recent photometric surveys, we estimate the interstellar extinction A_V towards the stars. Our analysis of à variations of the parameters A_V, P_max, λ_max in the sky plane and with the distance allows us to conclude that in the considered field (excluding the halo of B5) the main contribution to the extinction and polarization is provided by an extension of the Taurus cloud complex (TMC) at d ≈ 150 pc, and that the derived values of the parameters indicate that the angle between the line of sight and the magnetic field direction in this part of TMC significantly differs from 90°.

We have constructed an approximate analytic one-dimensional model of the accretion disk boundary layer surrounding a neutron star whose low magnetic field does not affect the process of accretion. We consider a high luminosity model with radiation pressure dominant in the interior part of the disk.

We studied the activity of the young K7V star TIC 88785435 and estimated a possible atmospheric mass loss from its exoplanet. TIC 88785435 is a member of the ϕ Lup subgroup, with an age of 9.9–17.7 Myr; the age of the star itself is 16.0 ± 1.6 Myr. according to our estimates based on TESS data, the star spots cover 6.3% and 10.5% of its visible surface area, which corresponds to absolute values of 43,000 and 71,300 millionths of the solar hemisphere (MSH) for Sectors 38 and 65, respectively. The most reliable flare detected from this star had a total emitted energy of 1.03·10³³ erg. The planet TIC 88785435 b is classified as a super-Neptune. It orbits the star with a period of 10.51 days, has a radius of R_b = 5.03R_⨁, and an estimated mass of M_b = 20.0M_⨁, based on empirical mass–radius relation (M–R). Atmospheric escape calculations using the energy-limited escape model revealed that the planetary mass-loss rate from TIC 88785435/b may lie in the range of 2.7·10⁸ g/s to 1.7·10⁹ g/s, depending on the level of stellar activity.

In this study, we analyzed the behavior of the bright solar-type star HD 111395, with the aim of further comparing its photospheric, chromospheric, and coronal activity. HD 111395 is found to exhibit a higher level of activity than the Sun. The rotation periods P_rot are in the range of 15.25 to 18.88 days, indicating a differential nature of surface rotation. Based on data from Sectors 23 and 49 of the TESS archive, estimates were made of the star’s spotting parameter and spot areas on its surface: 7,500 and 8,900 millionths of the solar hemisphere (MSH) for Sectors 23 and 49, respectively. These values exceed the solar mean values but are comparable to the maximum levels observed on the Sun. From Kamogata Wide-field Survey (KWS), activity cycle periods P_cycl of 930 days (2.5 years), 1,830 days (5.0 years), and 3,800 days (10.4 years) were identified, while ASAS measurements yielded a period of 1,800 days (4.9 years). The obtained results are compared with activity cycles previously established based on chromospheric indicators and long-term variations in X-ray flux.

The first in-depth photometric study of four δ Scuti stars was performed. We used time series data from the Transiting Exoplanet Survey Satellite (TESS) that is available in different sectors. According to the extracted maxima from TESS space-based observations, we calculated an ephemeris for each star. We estimated the physical parameters of the target stars based on the Gaia Data Release 3 (DR3) parallax method. The results obtained for the surface gravity of the stars are consistent with the reports of the TESS Input Catalog and Gaia DR3. We estimated the pulsating constant based on the physical parameters and period of the stars. Therefore, we found that the stars 2MASS 15515693-7759002 and 2MASS 07513202+0526526 belong to the fundamental, while 2MASS 00044615+4936439 and 2MASS 10215638-3326137 relate to the first overtone. The Fourier analysis using the Period04 program was done for each star. As we showed in the Hertzsprung-Russell (H-R) diagram, the stars are located in the instability strip of the δ Scuti stars region. Four target stars were found to be of the low-amplitude δ Scuti star type.

We study the time-like geodesics in the spacetime of the Rindler-modified Schwarzschild black hole (RMSBH) with a cosmological constant. We find that for massive particles, whether undergoing radial motion or orbital motion, are unable to escape the black hole. Meanwhile, at larger orbital radii, the cosmological constant significantly modifies the proper velocity of particles. Additionally, in the case where Λ = 0, we have presented a special solution: if the particle is located on a specific circular orbit, its proper velocity will remain unaffected by the Rindler acceleration. Furthermore, we discuss the stability of circular orbits by employing the Lyapunov exponent, and draw the dividing line between stable and unstable circular orbits.

The objective of the study is to investigate the dynamic behaviors of solar spicules and prominences and the relationship between them. An analysis of spicules and prominences and comparison of the obtained results should provide some novelty to the description of physical processes governing these phenomena. For this purpose, spectrograms in the helium D₃ line were obtained at a height of 8000 km using the large coronagraph at the Abastuman Astrophysical Observatory. The D₃ line spectrograms were derived in the second order, with an inverse dispersion of 0.96 Å/mm. The standard errors of the Doppler velocities and spectral line widths are 0.35 km/s and 0.04 Å, respectively. The lifetime of almost all measured spicules was about 20 min, which defines them as type I spicules. The Doppler shifts and variations of line widths over time were analyzed using the Lomb-Scargle periodogram algorithm for irregular data series. The primary results of the observational data reduction and analysis are as follows. The Doppler velocities in the prominence legs vary in the range of about 17–18 km/s, and in spicules in the range of 16–24 km/s. We observe a temporal asymmetry in the variation of Doppler velocities and line widths in four out of the five studied spicules. For D₃ prominences, the oscillation period of the Doppler velocities on average ranges from three to four minutes, and the period of line width oscillation from two to three minutes. For D₃ spicules, the period of Doppler velocity oscillations varies on average between two and five minutes, and the period of line width oscillation between two and five minutes. In the prominence legs, the anticorrelation between Doppler velocities and line widths is more pronounced in the region where solar plasma moves from lower atmospheric layers to higher ones. The observed anti-phase oscillations with longer periods can be explained by the upward and downward motion of turbulent plasma in type I spicules. Oscillations with shorter periods may be caused by the helical motion of the spicule axis resulting from the superposition of two linearly polarized magnetohydrodynamic kink waves.