Astronomy Reports最新文献

Black hole images obtained by very long baseline interferometry (VLBI) by the Event Horizon Telescope are a new tool for testing general relativity in super-strong gravitational fields. These images demonstrated a ring-like structure which can be explained as the black hole shadow image. To date, there are no reliable methods for determining the parameters of these ring-like structures, such as diameter, width, and asymmetry. In this paper, an algorithm for determining black hole image parameters is proposed using a Gaussian asymmetric ring as an example. Using the proposed method, the diameter and asymmetry parameters of the image of a supermassive black hole in the galaxy M87* were estimated based on observational data obtained by the Event Horizon Telescope group.

We consider some parameters of the astroclimate of two high-altitude observatories in Tajikistan—Sanglokh and Shorbulok. Long-term variations and seasonal features of the total cloud cover and the precipitated water vapor content are analyzed with the use of the ERA5 atmospheric reanalysis data (which is the fifth generation ECMWF reanalysis for the global climate and weather (where ECMWF stands for the European Centre for Medium-Range Weather Forecasts)). The trends observed since 1980 are estimated in terms of statistical significance. We present the results of measurements of the precipitated water vapor content and the near-surface wind speed at the Sanglokh observatory in 2024–2025.

Based on data of solar-type stars with superflares from the archive of the TESS space mission, the cyclical nature of their magnetic activity has been studied. Of the 711 stars with superflares selected according to papers by Tu (Tu Zuo-Lin) and co-authors, the KWS photometric archive of ground-based observations contains data for 401 stars (of which there are at least 300 brightness measurements for 331 stars). From this list of objects, manifestations of cyclical activity were detected in 115 objects. The relations between the values of rotation periods and cycles of activity of objects have been studied. It has been found that the corresponding diagrams indicate that the cyclic properties of the studied G-dwarfs with superflares coincide with other stars. This has made it possible to conclude that the mechanism of activity is likely to be common. The slope of dependence obtained by joint approximation by dominant cycles for G-dwarfs with superflares and other objects is equal to (1.03 pm 0.03), which corresponds to the available literature data. Probably, two sequences with the same slope, which may correspond to analogues of the Schwabe solar cycle and the cycle with duration of 2‒3 years, are distinguished in the diagram.

To optimize the search for (detection of) near-Earth asteroids (NEAs) is of practical interest. Almost all NEAs larger than ~700 m are known (more than 90%). However, the modern interpretation of the problem of detecting NEAs includes the requirement to detect a great number of asteroids larger than 10 m in size. So far, there are no detecting systems that meet this requirement, either in the world or in Russia, but work is underway to create them. This paper considers some of astronomical grounds for choosing an effective strategy in searching for NEAs, especially for asteroids that can enter the near-Earth space (NES), i.e., approach the Earth at a distance of less than 1.5 million km. In our paper, asteroids that are expected to enter the NES within the next 100 years are classified as close potentially hazardous asteroids (CPHAs). We constructed practically important distributions of asteroids across the celestial sphere, brightness, and angular velocity. As the comparison of the distributions built for the ensemble of all NEAs larger than 10 m (according to the NEOMOD simulator) and for the ensemble of CPHAs showed, the distributions of CPHAs over the celestial sphere and the angular velocity differ from the corresponding distributions of all NEAs. Particularly, in a wide interval of distances, from 0.1 to 0.5 AU, the mean angular velocities of CPHAs are on average an order of magnitude lower than those of all NEAs located at the same distances. When developing a strategy for detecting CPHAs, it is important to take into account the characteristics of their distributions.

The results of the analysis of photometric observations of the long-period SU UMa-type dwarf nova MASTER OT J212624.16+253827.2 are presented based on the ZTF, ATLAS, GAIA, and ASAS-SN data obtained in 2018–2023 (HJD 2 456 772–2  460  568) and the Crimean Astrophysical Observatory obtained in 2023–2024 (HJD 2 460 199–2 460 576) at different stages of outburst activity. We found that this observation interval is notable for variations in the supercycle and cycle of the dwarf nova, equal to ({{146}^{d}}{kern 1pt} - {kern 1pt} {{184}^{d}}) and ({{12}^{d}}{kern 1pt} - {kern 1pt} {{37}^{d}}), respectively. For the first time, we determined the orbital period equal to ({{0.0865044(2)}^{d}}), which dominated in the 2018–2023 (HJD 2 458 228–2 458 836) quiescence and the period of negative superhumps ({{0.083}^{d}}{kern 1pt} - {kern 1pt} {{0.084}^{d}}), which dominated in 2023–2024 (HJD 2460199–2460576) quiescence. The estimated mass ratio of the system components is 0.21(2).

Low efficiency of metal mixing in the interstellar gas leads to the fact that their inhomogenous spatial distribution persist in the medium for a long time. In this paper, we study the effect of variations in the elemental composition on the chemical evolution of molecular gas cooling behind the fronts of shock waves from supernovae. Numerical modeling of nonequilibrium chemical kinetics for the Lagrangian element of gas behind shock waves with velocities of 5–15 km/s is performed. The abundance of carbon and oxygen varied within ±0.3 dex from the characteristic values for the interstellar medium of the Galaxy. Significant deviations in the fractions of some molecules are found that are not proportional to the change in the abundance of the corresponding chemical elements. Moreover, these deviations significantly exceed the initial variations in the abundances of elements. The dependence of the deviation in the molecular fractions on the gas properties and external effects, such as: gas density, ultraviolet radiation flux, ionization rate by cosmic rays, and extinction is studied. With a variation in the oxygen abundance of δ[O/H] ∼ ±0.3 dex, the fractions of water molecules deviate from the corresponding value during evolution for the interstellar adundance by a factor of ∼3−50. The deviations are most significant for extinction A_V ∼ 0.3 − 3. The importance of the variations for the chemical kinetics of molecules in star-forming regions is discussed.

In an area of 3300 sq. deg, a search for pulse dispersed signals using a neural network has been carried out. When processing observations over an interval of six months, the pulses of fifteen known pulsars, as well as three new rotating radio transients (RRATs), have been found. For new sources, their main characteristics have been provided. The dispersion measure of transient and pulse half-width are in the ranges of 7.2‒59.9 pc/cm³ and 20–300 ms, respectively. An RRAT search scheme has been developed to detect pulses with a signal-to-noise ratio (S/N) below the threshold required for reliable detection.

Numerical simulations of the evolution of the Solar system consisting at the initial stage of five, six, seven, and eight outer planets, as well as a self-gravitating planetesimal disk, were carried out. The dynamical evolution of planetary systems was studied over a time interval of 4 Gyr. In most cases of numerical simulations, either the destruction of planetary systems or the transition of planets to orbits significantly different from modern orbits occurred. However, a number of successful variants, in which the configuration of the orbits of the outer planets after 4 Gyr was close to the present Solar system, were found. The ejection of additional planets can occur at all stages of the evolution of the Solar system. In the variant with eight planets, a case of an additional planet remaining in a distant trans-Neptunian orbit with a perihelion distance of q = 120 AU was found. Despite the great diversity of evolutionary paths of systems with additional planets, distant trans-Neptunian objects were registered in all successful variants. A trend towards an increase in the number of surviving distant trans-Neptunian objects with an increase in the number of additional planets was noted.

The basic properties of Be stars and X-ray binary systems containing these stars are considered. In the vast majority of these systems the Be stars’ companions are neutron stars accreting matter from the decretion disk of a rapidly rotating Be star. The observed properties of such systems are studied within the framework of the hypothesis that the reason for the high rotational velocity of Be stars is the large initial angular momentum of the protostellar cloud, and during the evolution of the star on the main sequence, the angular momentum is transferred from the interior of the star to the surface. The work uses the results of calculations performed earlier by the authors of the evolution of rapidly rotating Be stars, taking into account their stellar wind, which carries away the angular momentum of the outer layers of the star. Based on the rates of rotational mass loss by Be stars through the decretion disk, obtained in these calculations, it is estimated which part of the disk material is captured by the neutron star in observed X-ray binaries with Be stars. For systems with short orbital periods of about 30 days, the maximum value of this part can exceed 0.01. At the same time, for observed systems, this part significantly (sometimes by more than 2 orders of magnitude) exceeds the fraction of the Be star’s stellar wind captured by the neutron star.

As part of the Early Science Program of the RadioAstron project, the millisecond pulsar B1937+21 was observed in October 2012. The total duration of the experiment supported by eight ground-based radio telescopes was about three hours. The radiation in both circular polarizations in the frequency band of 1644‒1676 MHz was recorded. Characteristic time and frequency scales of scintillation caused by the scattering on the interstellar plasma density fluctuations have been measured: (Delta {{t}_{{{text{dif}}}}} = 275.2 pm 0.1) s and (Delta {{nu }_{{{text{dif}}}}} = 580 pm 30) kHz. The angular diameter of the scattering disk, ({{theta }_{{text{H}}}} = 0.32 pm 0.03) mas, has been estimated from the decrease in the amplitude of the interferometric response at the ground–space baselines. The dependence of the visibility amplitude on the delay shows two scattering time scales: ({{tau }_{{{text{sc}}1}}} = 110 pm 30) ns and ({{tau }_{{{text{sc}}2}}} = 750 pm 100) ns, which indicates an ellipse-like scattering disc with an axis ratio of 2.6 : 1. The drift of the visibility maximum on the residual interference frequency that was observed at the intercontinental baselines can be explained by atmospheric effects, while the dominant contribution being the additional phase shift in the troposphere above European stations.