Astronomy Reports最新文献

Recently, it has been suggested in the literature that the difference between universal and coordinated time UT1–UTC could reach a large positive value in the coming years [1]. This would make it necessary to introduce a negative leap second into UTC for the first time in history, which in turn will cause serious problems in time keeping and synchronization systems around the world. Based on the latest Earth’s rotation and universal time data published by the international Earth rotation and reference systems service (IERS) and their prediction, in this paper, we have shown that the acceleration trend observed over the past four years is likely to return to slowing down soon. Therefore, fears about the possible need to introduce a negative leap second into the UTC time scale in the next few years in the light of recent observational data have seen unfounded.

In this paper, we have analyzed the properties of the photometric and spectral variability of young star V718 Per, a member of the cluster IC 348, in terms of its possible binarity. The most realistic is the model where the main component of the V718 Per A system—with an effective temperature of 5200 K—is periodically shielded by two extended dust structures consisting of large particles and moving around the star in resonance with two planets. Their orbital periods are 4.7 years and 213 days. Their ratio with high accuracy is equal to 1 : 8, and the ratio of the large semi-axes is 1 : 4. The masses of the planets have not exceeded (6 ,{{M}_{{{text{Jup}}}}}). At the moments of total eclipses V718 Per A, the radiation of the system has been dominated by a colder component with an effective temperature of (4150 pm 100) K, which has explained the reddening of the star observed in the brightness minima, as well as its spectral changes during brightness weakening. Speckle interferometric observations performed using the 2.5-m telescope of the Sternberg Astronomical Institute have made it possible to estimate the upper limit of the angular distance between the components of the system: ≤0.1('' ), which is equivalent to a projection distance of ≤30 AU. The unique feature of this system has been that the planes of the planetary orbits practically coincide with the line of sight. Such an orientation of the system has been most favorable for measuring fluctuations in the radial velocity of a star caused by the orbital motion of planets, as well as for observing planetary transits along the disk of the main component of the system.

The aim of the work is to derive a new dynamic formula for the angular velocity of rotation of equilibrium figures of a gravitating fluid with a polytropic equation of state. In this formula, the angular velocity of rotation depends not only on the polytropic index (0 leqslant n leqslant 5,) but, most importantly, on the components of the internal and external gravitational energy of the figure. When solving the problem, the integration constant in the full potential was expressed through three global characteristics: mass, full gravitational energy and rotation energy of the equilibrium figure. The validity of the new formula was confirmed by the limiting transition at (n = 0) to classical homogeneous Maclaurin spheroids and Jacobi ellipsoids. The results of the work expand the scope of application of the theory of equilibrium figures.

The processes of formation and six mechanisms of disintegration of open star clusters (OSCs) are considered. Analytical estimates of the rates of OSC disintegration are made for the following mechanisms: loss of the initial gas component of OSCs, mass loss due to supernovae explosions and planetary nebula formation, pair interactions of OSC stars, acceleration of stars by binary systems of OSCs, interaction of OSC stars with stars of the Galactic disk, collisions of OSCs with giant molecular clouds (GMCs) at the front of a spiral wave. The destruction of OSCs is accompanied by the formation of a stellar stream. An analysis of the radius–mass ratio of the OSC core (RM) allowed us to conclude that it probably does not reflect the disintegration mechanism and is a product of observational selection effects. The evolution of an individual OSC in the R–M plane is determined by the initial density and external conditions.

We consider photometric behavior of the spotted primary in V772 Her, an eclipsing system of dwarf stars (G0V + M5V), on the base of many-year multicolor photoelectric observations. The combined photometric effect due to spots can be as large as ({0}_{.}^{{text{m}}})19. Our modeling demonstrated that the area of spotted regions can reach 13% of the star’s total surface area. Spots are cooler than the undisturbed photosphere by 1800 K and are located at low latitudes.

The results of the study of the star formation region G 109.871+2.114 (Cep A) in OH lines at 18 cm are presented. Polarization observations (monitoring) were performed with a large Nançay radio telescope (France) in 2007–2024. OH maser emission is highly variable. The structure of the spectrum and the flux density of the individual spectral features are changing. However, the radial velocities of most features changed slightly. Short-term emission flares in individual features were observed. Many features have strong circular polarization, reaching 100%, but have weak linear polarization. A new features at –15.53 km/s and a short-term part at 1.58 km/s with high circular and low linear polarizations were detected in the 1667 MHz line. The spectral features of our monitoring were spatially identified with the maser spots on the Cohen, Argon, and Fish maps. The magnitude of the monotonic decrease in splitting, and, consequently, the longitudinal magnetic field of three Zeeman pairs (–16.2L/–14.25R and –6.94L/–0.82R km/s in the 1665 MHz line and –15.76L/–14.2R in the 1667 MHz line). For the –13.95L/–11.60R pair, no splitting change was detected in the 1665 MHz line. Broadband absorption and emission are observed in the satellite lines of 1612 and 1720 MHz, respectively. A Zeeman pair was also detected in the 1720 MHz line. The position angle (chi ) is calculated for linearly polarized emission of most spectral features in both main lines at 1665 and 1667 MHz. It is shown that the magnetic field in the H II regions is oriented either along the external magnetic field or along the radio jets.

The kinematic properties of the Sco-Cen association have been studied using the spatial velocities of young stars. New kinematic age estimates for the three components of the association with the age of UCL and LCC being (17.7 pm 2.4) Myr and the age of US being (6.4 pm 1.7) Myr have been obtained. The parameters of the residual velocities US, UCL, and LCC ellipsoid have been estimated.

The present paper explores the linear stability of the equilibrium points in the elliptic restricted three-body problem when the more massive primary is oblate and serves as a source of radiation, while the smaller primary is a radiating body. We have investigated the linear stability of these equilibrium points and observed that the collinear ones are unstable, whereas the non-collinear equilibrium points exhibit stability. Additionally, we have analyzed the combined influence of the oblateness parameter and the radiation factors of both primaries, ({{q}_{i}}), (i = 1,2,) on the position of equilibrium points. Our observations indicate that as the radiation factor ({{q}_{1}}) of the more massive primary decreases, the number of equilibrium points increases.

The previously developed method for estimating of the parameters of proton fluxes from flare energies for the Sun has been applied to data on the flare activity of solar-type stars. The obtained results will be used to estimate the radiation situation in a stellar system containing exoplanets. In our analysis, we have used catalog data on flares of solar-type stars obtained from observations with Kepler telescope. The empirical relations between the energy of X-ray flares and the proton flux for the Sun have been extended to the case of stellar flares, similar to what has been done previously in the case of coronal mass ejections (CMEs). The used method has had limitations caused by the extension of the solar analogy to other stars as well as the uncertainties that have arisen when applying scaling methods. It has been found that the characteristic values of the proton flux for solar-type stars can be one order of magnitude higher than the estimates for the Sun. Prospects for the development of alternative methods for estimating proton fluxes in the vicinity of stars of late spectral types have been discussed (for example, by studying the behavior of Si IV and He II emission lines in the far ultraviolet range).