Astronomičeskij žurnal

For the numerical model in the range of redshifts \(0 \leqslant z \leqslant 9\), we examined the properties and evolution of dark matter haloes using a previously proposed method of compact analysis that allows separating the influence of random and regular factors on the main characteristics of the dark matter halo. In the investigated range of redshifts, a monotonic evolution of the average values of the basic parameters of small halo structures into a central massive object is observed through sequential hierarchical merging. These basic parameters include the circular velocity \( {{{v}}_{c}} \), the parameter \( {{w}_{c}} = {{{v}}_{c}}{\text{/}}r \), and the mass. In the range \(3 \leqslant z \leqslant 9\), the parameters evolve slowly, while in the range \(0 \leqslant z \leqslant 3\), they evolve rapidly. The evolution of the dark matter halos formed before reionization is characterized by a slow change in their average characteristics and the properties of the halo outskirts. The important role of early-formed massive structural elements is emphasized.

Explaining the causes of angular momentum transfer in accretion stellar disks is an important astrophysical problem, since it is the process that determines the rate of accretion of matter onto the central gravitating body. Previously, within the framework of a two-dimensional approach, it was shown that the introduction of small perturbations into the flow of disk matter leads to the appearance of shear instability. This process is accompanied by the development of large-scale vortex structures. Their movement and evolution lead to a redistribution of angular momentum in the accretion disk. The action of the described mechanism was previously studied numerically only within a two-dimensional approximation, so the goal of the current work is to carry out full-scale three-dimensional modeling. The processes under study are described within the framework of the system of equations of ideal gas dynamics. The article briefly describes the method for their numerical integration, which is based on a conservative finite-difference scheme and the solution of the Riemann problem. The initial data is a stationary toroidal gas state surrounded by a matter with low density and pressure. At the next step, small perturbations of one of the gas-dynamic variables are introduced. The modeling and analysis of the results of numerical calculations show the emergence of vortex structures in the shear flow of a three-dimensional accretion disk. Their movement is accompanied by a redistribution of matter and angular momentum in the volume of the disk, leading to accretion of matter onto the central body.

The paper presents 1D aeronomic model of hydrogen-helium upper atmospheres of hot giant exoplanets based on the approximation of single-fluid multicomponent hydrodynamics. Chemical reactions and heating-cooling processes are taken into account. Typical hot Jupiter and warm Neptune are considered as an example of the application of the model. Calculations were carried out for various values of gas pressure at the photometric radius of the planet. In the solutions obtained, a transonic planetary wind is formed, leading to a hydrodynamic outflow of the atmosphere with mass loss rates of the order of \(3.5 \times {{10}^{{10}}}\) g/s for hot Jupiter and \(3.7 \times {{10}^{9}}\) g/s for warm Neptune. At the same time, the outer layers of the atmosphere of hot Jupiter are completely ionized, while the atmosphere of warm Neptune mainly consists of neutral gas. In some variants of the hot Jupiter model, instability develops in the deep layers of the atmosphere, which can lead to the formation of a specific cloud layer.

The results of spectral observations in the \( \sim {\kern 1pt} 84{\kern 1pt} - {\kern 1pt} 92\) GHz frequency range of six objects from the southern sky having dense cores and associated with massive star and star cluster forming regions are presented. The observations are carried out with the MOPRA-22m radio telescope. Within the framework of the local thermodynamic equilibrium (LTE) approximation, column densities and abundances of the H¹³CN, H¹³CO⁺, HN¹³C, HC₃N, c-C₃H₂, SiO, CH₃C₂H and CH₃CN molecules are calculated. Kinetic temperatures (\( \sim 30{\kern 1pt} - {\kern 1pt} 50\) K), sizes of emission regions (\( \sim 0.2{\kern 1pt} - {\kern 1pt} 3.1\) pc) and virial mass esimates (\( \sim 70{\kern 1pt} - {\kern 1pt} 4600{\kern 1pt} {{M}_{ \odot }}\)) are obtained. The linewidths in the three cores decrease with increasing distance from the center. Four cores exhibit asymmetry in the profiles of the optically thick HCO⁺(1–0) and HCN(1–0) lines, indicating the presence of systematic motions in the line of sight. In two cases, the asymmetry can be caused by contraction of gas. The model HCO⁺(1–0) and H¹³CO⁺(1–0) spectral maps obtained within the non-LTE spherically symmetric model are fitted into observed ones. Radial density (\( \propto {\kern 1pt} {{r}^{{ - 1.6}}}\)), turbulent velocity (\( \propto {\kern 1pt} {{r}^{{ - 0.2}}}\)) and contraction velocity (\( \propto {\kern 1pt} {{r}^{{0.5}}}\)) profiles in the G268.42–0.85 core are obtained. The contraction velocity radial profile differs from expected both in the case of free fall of gas onto a protostar (\({{r}^{{ - 0.5}}}\)), and in the case of global core collapse (contraction velocity does not depend on distance). A discussion of the results obtained is provided.

New results of photometric observations of the chromospherically active star FK Com (a prototype of the group of the same name) performed during the past 5 years (2018–2023) at the INASAN observatories in Zvenigorod, Simeiz Observatory INASAN and Russian–Cuban Observatory in Havana, Republic of Cuba, are presented. In total during this observation interval we obtained 9060 estimates of the brightness of the star in V band. Our measurements as well as data from the literature and from the Kamogata Wide-field Survey (KWS) archive were combined into the array comprising 17 653 measurements in an interval of about 57 years. Based on the power spectrum constructed from these data, P values of the cycle activity have been established, which according to our estimate are equal to 2.4, 5.63, 8, 13.6, 30 and 49 years. The dominant is the P cycle lasting 5.63 years. It is shown that this dominant cycle with a period of about 5.63 years found by us according to more extensive data (5.4–5.8 years in other sources) can be traced in the results of the analysis of previous studies. The results on the activity cycles of FK Com are compared with data on the long-term variability of two more stars of the type under consideration – HD 199178 (V1794 Cyg) and ET Dra. Based on the data on the P cycle of other chromospherically active stars (according to literature sources and our measurements) a diagram \(\log (1{\text{/}}{{P}_{{{\text{rot}}}}}){\kern 1pt} - {\kern 1pt} \log ({{P}_{{{\text{cycl}}}}}{\text{/}}{{P}_{{{\text{rot}}}}})\) is analyzed. The conclusion about the comparability of the values of the activity cycles of the FK Com type stars with the data for stars of the RS CVn type is made.

The kinematics of stars from the solar neighborhood with a radius of 300 pc has been studied using the Gaia DR3 data. Our sample includes n = 970 171 stars – AG300 (A – ensemble, G – Gaia, 300 – radius of the studied zone in pc). The kinematics of these stars reflects the morphology of the main stellar populations of the Galaxy: the stellar disk, bulge, halo, and stellar corona of a supermassive black hole (SMBH). The presence of stars in AG300 with velocities exceeding the escape velocity from the Galaxy indicates the presence in the circumsolar space of extragalactic stars belonging to the stellar component of the local cluster of galaxies. It is shown that the known mechanisms of acceleration of the spatial motion of stars make it possible to create a stellar halo of galaxies, a stellar corona of SMBH in its core, an intergalactic stellar medium of galaxy clusters, and spaces between galaxy clusters. The AG300 catalog makes it possible to identify representatives of all named components.

The frequency and rate of solar nanoflares (NF) were measured in 6 coronal spectral ranges (094, 131, 171, 193, 211, 335 Å) and one, related to the transition layer (304 Å). We used SDO/AIA data obtained at solar minimum in May 2019. We analyzed the same region of the Sun, covering \(360\text{\textquotedblleft} \times 720\text{\textquotedblleft}\) field-of-view, in all channels over the same time interval of 1 hour. In all the spectral bands, to search for NF we applied the same algorithm based on the amplitude analysis of fast brightenings in AIA images. The frequency and rate of NF, as can be expected, vary significantly in different wavelengths. For threshold \(5\sigma \), the highest NF frequency, 207 c^–1, was measured in 171 Å. The next spectral ranges are 193 Å (85% of 171 channnel), 211 Å (74%), and 131 Å (63%). We have not been able to reliably measure the frequency in channels 094 Å, and 335 Å, but found that it is less than 15% of the frequency in channel 171 Å. In the 304 Å channel, we found a large number of brightenings that do not match any coronal events. However, about 40% of NF in corona have a counterpart in the 304 Å line with an amplitude higher than \(5\sigma \).