Abstract Based on spectrophotometric observations, we have studied the variable activity of the symbiotic star CH Cyg from 2008 to 2018. The activity of the star was accompanied by a periodic increase of the flux in continuum and spectral lines. In the period of its activity, in both 2015 and 2018, absorption components appeared in the profiles of emission lines. The shape and radial velocity of the

Abstract The purpose of the present paper is to investigate the motion’s properties of an infinitesimal body in three-dimensional version of Hill’s problem where the mass of the infinitesimal body is supposed to vary with time. As commonly done, the infinitesimal body is assumed to move under the influence of the other massive and oblate bodies that also have radiation effects. We suppose that the

Abstract For the first time we have explored the effects of the magnetic field in a nova shell on the escape of positrons from the radioactive isotope \({}^{22}\)Na and on the evolution of the flux in the 511 keV annihilation line. We show that for a white dwarf surface magnetic field \({\sim}10^{6}\) G the magnetic field in an expanding nova shell is able to significantly impede the positron escape

Abstract The magnetar SGR J1745–2900 located in the vicinity of the supermassive black hole Sgr A\({}^{\star}\) was detected during its X-ray outburst with the Swift/XRT telescope in April 2013. For several months after its detection the source was observed with the NuSTAR observatory, which allowed pulsations with a period \({\sim}3.76\) s to be recorded. Using these observations, we have studied

Abstract The reduction of all the available photometry for the Cepheid SU Sct has allowed its \(O-C\) diagram spanning a time interval of 60 years to be constructed. Six abrupt changes in the period have been detected. The pulsation stability test proposed by Lombard and Koen (1993) has confirmed that the changes in the period are real. The absolute magnitude of SU Sct is \(M_{V}\simeq{-}0\overset{\textrm{m}}{

Abstract The plasma opacity in stars depends mainly on the local state of matter (the density, temperature, and chemical composition at the point of interest), but in supernova ejecta it also depends on the expansion velocity gradient, because the Doppler effect shifts the spectral lines differently in different ejecta layers. This effect is known in the literature as the expansion opacity. The existing

Abstract We have performed Monte Carlo simulations of the trajectories of several runaway stars using their parallaxes and proper motions from the Gaia EDR3 catalogue. We have confirmed the hypothesis that the stars AE Aur and \(\mu\) Col are a product of the multiple system breakup \({\sim}2.5\) Myr ago and the Orion Trapezium may be the parent cluster for this pair of stars. We show that the data

Abstract Based on highly accurate data from the archive of the TESS space mission, we have studied the photometric variability of the K1-type dwarf AB Pic (HD 44627), which is a member of the Tuc–Hor association and possesses a distant giant planet with a mass of 13.5 Jupiter masses. In the interval of its TESS observations 48 flares with an energy in the range \(6.1\times 10^{32}{-}3.4\times 10^{35}\)

Abstract During the first all-sky survey of the SRG orbital observatory, the X-ray source SRGE J170245.3+130104 was discovered with the eROSITA telescope on March 13–15, 2020. Its optical counterpart was identified by photometric attributes as a candidate for distant quasars at \(z\approx 5.5\). The spectroscopic observations of the object carried out in August and September 2020 at the 6-m BTA telescope

Abstract In view of the absence of a satisfactory solution to the globular cluster (GC) classification problem, we have searched for a physical parameter that admits of the GC classification and finding empirical dependences on observed physical characteristics. For this purpose, we have considered a model of the apparent density in GCs with three free parameters. Using the widely known simplex method

Abstract We present the first results of our program of optical observations for galaxy clusters from the Lockman Hole X-ray survey with the eROSITA telescope onboard the SRG space observatory. We present the results of spectroscopic redshift measurements for 11 galaxy clusters that have been identified optically among the extended X-ray sources of the SRG/eROSITA survey using data from optical and

Abstract We have carried out a systematic analysis of the light curves of gamma-ray bursts (GRBs) detected in the SPI-ACS experiment onboard the INTEGRAL observatory to search for extended emission. The emission occasionally recorded after the prompt active phase of a GRB in the form of an emission that is longer than the active phase and less intense is called the extended one. Out of the 739 brightest

Abstract We present the results of our analysis of the optimal flight to the trans-Neptunian object (90377) Sedna at the launch in 2029. Sedna is a distant space object with a perihelion and aphelion \({\sim}74\) and 1000 AU, respectively, suggesting that this celestial body may belong to the Oort cloud. The orbital period of Sedna is more than 11 000 years. In our study we have considered a direct

Abstract We have studied stellar candidates for close (within 1 pc) encounters with the Solar system. For all of the stars under consideration the kinematic characteristics have been taken from the Gaia EDR3 catalogue. The parameters of the encounters of these stars with the Solar system have been calculated using three methods: (1) the linear one, (2) by integrating the orbits in an axisymmetric potential

Abstract Globular clusters \((GCs)\) are among the oldest stellar systems in the early universe. We present galaxies formed with two different stellar populations, which depend on the relation between mass and radius. The primordial values of the number of globular clusters can be distinctly separated into two groups of densities, and thus are dependent on galaxy mass. Evidence that dE and E galaxies

Abstract We present the results of our spectroscopic redshift measurements for galaxy clusters detected previously from Planck all-sky survey data as well as Sloan Digital Sky Survey and WISE all-sky survey data. The redshifts have been measured for 23 clusters, including four galaxy clusters from the second Planck catalogue of Sunyaev–Zeldovich sources. The main spectroscopic observations were carried

Abstract The Baikal-GVD deep underwater neutrino experiment participates in the international multi-messenger program to detect the astrophysical sources of high- and ultrahigh-energy cosmic-ray particles, being at the stage of array deployment and a step-by-step increase of the telescope’s effective volume to the scale of a cubic kilometer. At present, the telescope consists of seven clusters containing

Abstract We present the results of our identification of eight objects from the preliminary catalogue of X-ray sources detected in the 4–12 keV energy band by the Mikhail Pavlinsky ART-XC telescope onboard the SRG observatory during the first all-sky survey. Three of them (SRGA J005751.0+210846, SRGA J\(014157.0{-}032915\), SRGA J232446.8+440756) have been discovered by the ART-XC telescope, while

Abstract Based on the data obtained with the CHIMERA algorithm, we consider the evolution of a long-lived low-latitude coronal hole during its central meridian passage over the period from February 15, 2012, to October 14, 2012. The correlation coefficient between the photospheric magnetic field strength of the coronal hole and its area in nine Carrington rotations is \(R={-}0.55\). It differs noticeably

Abstract The emission from the Crab nebula exhibits a significant gamma-ray variability. In this paper we have analyzed this variability in terms of periodicity. Using the pulsar ephemeris constructed from radio data, we have obtained the light curve of the Crab nebula with the suppressed contribution of the pulsar in the energy range 100–300 MeV from August 2008 to March 2020. Using analysis of variance

Abstract The reduction of all the available photometry for the Cepheid V420 Cen has allowed its \(O-C\) diagram spanning a time interval of 131 years to be constructed. The data obtained provide evidence for the existence of large random fluctuations in the period (\(\varepsilon/P\approx 0.021\)). Fitting the \(O-C\) residuals by a cubic parabola has made it possible to estimate the rate of secular

Abstract Interstellar dust (ISD) penetrates into the heliosphere due to the relative motion of the Sun and the local interstellar medium (LISM). Inside the heliosphere and at the boundaries, where solar wind interacts with the LISM, distribution of ISD is modified due to the action of the electromagnetic forces, the solar gravitation and the radiation pressure. These forces make the distribution of

Abstract A method of correcting the statistical data of the exoplanets discovered through radial velocity measurements is proposed. The statistical regularities of the mass and orbital period distributions of exoplanets have been analyzed.

Abstract We have studied the light curves of type Ia supernovae (SNe Ia) and the physical parameters inferred from them. We have constructed both analytical and numerical light curves of SNe Ia. Using an empirical relation between the SN luminosity and light-curve parameters, we have managed to impose constraints on the hydrodynamic solutions obtained by the STELLA code and to produce a sample of models

Abstract For two classical Cepheids, CEa Cas and CEb Cas, members of the open cluster NGC 7790, we have constructed \(O-C\) diagrams spanning a time interval of 125 years. The \(O-C\) diagrams have the shape of parabolas, which has allowed us for the first time to determine the quadratic light elements and to calculate the rates of evolutionary changes in their periods: \(dP/dt={-}0.038({\pm}{0.017})\)

Abstract Several years ago a series of powerful millisecond radio bursts with close dispersion measures was detected toward the galaxy M31. Taking the hypothesis about the possible association of these radio bursts with a magnetar in M31 as a starting point, we have searched for periodic X-ray signal sources using data from the XMM-Newton X-ray telescope. As a result of our data analysis, we have identified

Abstract Variable circumstellar extinction models as applied to T Tauri stars are considered. In contrast to hotter UX Ori stars, for which simplified eclipse models are applicable, the star is deemed a point source of light, while the circumstellar dust clouds obscuring the star are assumed to be homogeneous. In the case considered here, both these simplifications may not work. Hot accretion spots

Abstract The technique of coronal mass ejection (CME) mass estimates from the energy of stellar flares has been applied to the data on the flare activity of late-type stars. In this study we use the data from catalogs on stellar flares obtained from the results of observations with the Kepler Space Telescope and present the relations between CME mass and effective temperature for objects from these

Abstract Multicolor photometric observations in the optical band and a comprehensive study in the X-ray, gamma-ray, and radio bands are presented for GRB 181201A and its afterglow. The optical observations began \({\sim}0.5\) day after the burst and lasted almost continuously for \({\sim}24\) days. They were resumed after eight months, which allowed us to determine the contribution of the host galaxy

Abstract Two algorithms for reconstructing the distribution of accretion spots over the surface of white dwarfs in AM Her variables are described. Both algorithms suggest the use of photopolarimetric observations. In the first case, the assumption that the spots are geometrically thin is used, while the white dwarf magnetic dipole orientation and the accretion spot position are found by fitting the

Abstract The Transient Double-beam Spectrograph (TDS) is designed for low-spectral-resolution optical observations of nonstationary and extragalactic sources at the 2.5-m telescope of the Caucasus Mountain Observatory (CMO) of SAI MSU. The spectra are recorded simultaneously in two channels, short-wavelength (360–577 nm, reciprocal dispersion 1.21 Å/pixel, resolution \(R=1300\) with a \(1^{\prime\prime}\)-wide

Abstract Observations of individual pulses from the pulsar PSR B1530+27 have been carried out. The dispersion measure (DM) toward this pulsar has been found from 11 084 pulses to be \(DM=14.6904\pm 0.0009\) pc cm\({}^{-3}\). The (\(3\sigma\)) upper limit on the DM derivative is \(|dDM/dt|<0.001\) pc cm\({}^{-3}\) yr\({}^{-1}\). The seasonal DM variations related to the passage of radiation through

Abstract The linear increase of the cosmic microwave background (CMB) temperature with cosmological redshift, \(T_{\textrm{CMB}}=T_{{0}}(1+z)\), is a prediction of the standard cosmological \(\Lambda\)CDM model. There are currently two methods to measure this dependence at redshift \(z>0\) and, what is equally important, to estimate of the CMB temperature \(T_{0}\) at the present epoch. The first method

Abstract The possibility of the existence of radiation belts near a planet possessing an intrinsic magnetic field and located in a stellar plasma flow is considered using Mercury as an example. An analysis is performed both using Størmer’s theory of charged particle motion, in which not the specific trajectories of individual particles, but the regions of allowed motion in an axisymmetric field are

Abstract Stellar evolution calculations for population II stars with initial composition \(Y_{0}=0.25\), \(Z_{0}=10^{-3}\) and the initial stellar mass \(M_{0}=0.82M_{\odot}\) were carried out from the main sequence to the white dwarf stage. Twelve AGB and post-AGB evolutionary sequences were computed with different values of the parameter in the Blöcker mass loss rate formula (\(0.01\leq\eta_{\textrm{B}}\leq

Abstract We present the results of long-term photometric monitoring of two active galactic nuclei, 2MASX J08535955+7700543 (\(z\sim 0.106\)) and VII Zw 244 (\(z\sim 0.131\)), being investigated by the reverberation mapping method in medium-band filters. To estimate the size of the broad line region, we have analyzed the light curves with the JAVELIN code. The emission line widths have been measured

Abstract The SDO/AIA 193 Å and ACE/SWEPAM data acquired in 2019 are used to compare the effects of polar and equatorial coronal holes (CHs) on solar wind (SW) characteristics under conditions of low solar activity. As expected, most geomagnetic storms in this period were caused by high-speed SW streams (\({>}500{-}600\) km s\({}^{-1}\)) originating from equatorial CHs. At the same time, it has been

Abstract Extensive numerical experiments on the long-term dynamics of planetesimals near the orbits of planets around single stars with debris disks have been carried out. The radial sizes of planetesimal clusters and the planetary chaotic zone as a function of mass parameter \(\mu\) (planet–star mass ratio) have been determined numerically with a high accuracy separately for the outer and inner parts

Abstract Based on the previously proposed steady-state 3D model of a solar facular knot, we have developed its modified version in which the solitary nature of the facular object is reflected: its magnetic field is sharply bounded in the radial direction. The facula temperature profile calculated for the steady state of such a magnetic structure is compared with the high-resolution filtergram taken

Abstract We analyze the minimum orbital intersection distances (MOIDs) for a sample of long-period comets (1360) and the giant planets of the Solar System. Our calculations have revealed a considerable number of long-period comets that may have had close encounters with the giant planets: Jupiter (268), Saturn (176), Uranus (81), and Neptune (75). Among them there are 107 cases where the comet approaches

Abstract The spatial distribution of the north–south (N–S) asymmetry over 1977–2001 is studied. A comparison of the distributions and time variations of the asymmetry index \(A\) in the green coronal Fe XIV 530.3 nm line, in the total coronal magnetic field, and in small- and large-scale fields has shown that at low latitudes the distribution of \(A\) for small-scale fields bears the greatest similarity

Abstract In 2012–2014 we obtained 3296 CCD frames in the \(BVI_{c}\) photometric system for the RR Lyrae star T Men with the 76-cm telescope of the South African Astronomical Observatory (SAAO, SAR) and the 1-m telescopes of the Las Cumbres Observatory Global Telescope (LCOGT). Our observations showed a slightly increased scatter of data points on the light curve, which allowed the Blazhko effect with

Abstract A model of a population of ultraluminous X-ray sources with magnetized neutron stars (NULXs) in a spiral galaxy with a star formation history as in the thin disk of the Milky Way is constructed by the hybrid population synthesis method. First, based on analytical approximations (BSE code), we compute a set of close binary systems (CBSs), potential precursors of NULXs, and, then, the evolution

Abstract Results of the first spectroscopic observations at the 1.5-m Russian–Turkish telescope for the X-ray sources discovered by the eROSITA telescope onboard the SRG space observatory and identified by the SRGz machine learning system as candidates for distant X-ray quasars are presented. Seven objects have been confirmed as quasars at redshifts \(z=2.7{-}4.2\) and two sources, which were included

Abstract Results of the first multicolor photometric observations of the unusual dwarf nova V2466 Cygni during its 2003 and 2019 superoutbursts are presented. The total amplitude of the 2019 superoutburst in the \(R_{c}\) band is 7.4 magnitudes. A single rebrightening was observed at the end of the 2019 superoutburst. While analyzing the \(O-C\) diagram for the superhumps, we identified pronounced

Abstract A detailed analysis of the GBM/Fermi experiment data is carried out to classify GRB 200415A. It is shown that, on the one hand, this event exhibits typical for type I (short) gamma-ray bursts (GRBs) properties, such as duration, variability, and the character of spectral evolution (lag). On the other hand, the localization of the event source on the celestial plane, obtained by the triangulation

Abstract We have constructed a new K I model atom using currently available atomic data. We have performed calculations for K I by abandoning the assumption of local thermodynamic equilibrium (non-LTE) for the Sun and three moderately metal-poor dwarf stars. To take into account the inelastic processes in collisions with hydrogen atoms, for the first time we have used the rate constants calculated

Abstract H 3-75 is a medium-excitation planetary nebula with a binary central star consisting of a hot subdwarf with \(T_{\textrm{hot}}\sim 10^{5}\) K and a cool giant. We present the results of our photometric and spectroscopic observations obtained in 2020 and analyze data from the literature. The brightness of the cool component of the binary system has been measured in the \(VR_{C}I_{C}JHK\) bands

Abstract Based on archival Hubble Space Telescope images, we have performed stellar photometry for the spiral Seyfert galaxy NGC 1672 located in the Dorado (Goldfish) galaxy group. The distance to this galaxy measured by the TRGB method (\(D=15.8\pm 0.8\) Mpc) has shown that NGC 1672 does enter into the Dorado group. We have identified stars of various ages and luminosities on the Hertzsprung–Russell

Abstract The reduction of all the available photometry for the Cepheid CC Lyr has allowed its \(O-C\) diagram spanning a time interval of 124 years to be constructed. The data obtained provide evidence for the existence of large random fluctuations in the period (\(\varepsilon/P\approx 0.046\)). A formal fitting of the \(O-C\) residuals has made it possible to estimate the rate of secular increase

Abstract Only a handful of quadruple systems with two accurate inner visual orbits are known. The architecture of two such systems is studied here to determine the period ratios, mutual orbit orientation, and other parameters; updated orbital elements and their errors are derived. Gliese 225.1 (HIP 28442) is composed of three K-type and one M-type dwarfs and has inner orbital periods of 67.2 \(\pm\)

Abstract A novel method is proposed for the reconstruction of the early bolometric light curve for supernovae IIP with the available set of H\(\alpha\) emission spectra on the first day after the shock breakout. The method uses the effect of radiative acceleration of the preshock circumstellar gas that is manifested in broad H\(\alpha\) wings. The efficiency of the method is demonstrated in the case

Abstract The apparent motion parameter (AMP) method is designed to determine the orbits of wide pairs of double stars with orbital periods of hundreds and thousands of years. This is a dynamical method using all that is known about the star at one moment to reconstruct its complete orbit within the two-body problem. The Gaia DR2 catalog contains all of the data for epoch 2015.5 that are needed to use

Abstract The nucleosynthesis of heavy elements in the scenario for the evolution of a close binary of neutron stars differing greatly in mass is considered. In contrast to the scenario for the merger of two neutron stars of comparable masses considered repeatedly in the literature, the evolution of such a binary at the final stage consists in a rapid mass transfer to the more massive star and an explosive

Abstract Based on SDSS data, we consider the fraction of active galactic nuclei among polar-ring galaxies. We have found evidence for an excess of Seyfert galaxies and LINERS among polar-ring galaxies compared to ordinary objects. The observed nuclear activity of polar-ring galaxies may be associated with the accretion of gas from the region of the polar structures onto the central galaxies.

Abstract The technique of spherical harmonics, both scalar and vector ones, has long been applied to analyze the astronomical data on a sphere, for example, in the representation of systematic errors, in stellar kinematics. Up to now, spherical harmonics have been used exclusively in heliocentric coordinate systems: the equatorial or Galactic one. To study the kinematics of the entire Galaxy (and not

Abstract Evidence of wind variability and velocity stratification in the extended atmosphere has been found in the spectra of the supergiant V340 Ser (\({=}\)IRAS 17279\(-\)1119) taken at the 6-m BTA telescope with a resolution \(R\geq 60\,000\). The H\(\alpha\) line has a P Cyg profile whose absorption component (\(V_{\odot}={+}34\) km s\({}^{-1}\)) is formed in the upper layers of the expanding atmosphere

Abstract On the basis of consistent stellar evolution and nonlinear stellar pulsation calculations, the Cepheid V1033 Cyg is shown to be the post-main sequence star at the first crossing of the instability strip during the gravitational contraction of the helium core. The observed light variability of V1033 Cyg is due to the radial oscillations in the fundamental mode. The best agreement (within one

Abstract The formation of the rubidium resonance lines is considered by taking into account the effects of departures from local thermodynamic equilibrium (LTE). A rubidium model atom has been constructed using 29 Rb I levels and the Rb II ground level. Non-LTE calculations have been performed for a grid of model atmospheres with \(T_{\textrm{eff}}\) from 3500 to 6500 K, \(\log g\) from 1.0 to 5.0

Abstract The laboratory simulations of jets from young stars that have been carried out for many years at plasma focus facilities allow the internal structure of the active regions emerging during the interaction of the jet with the surrounding plasma to be studied in detail. We have found a new wide class of solutions for the equations of ideal magnetohydrodynamics describing the closed axisymmetric