Astronomy Reports最新文献

The problem of equilibrium figures of two liquid masses in a state of tidal mutual capture is posed and solved. The condition of complete synchronous (orbital plus spin) rotation is satisfied in the system, and both bodies have the same masses and congruent ellipsoidal surfaces. For each figure, besides its own gravity and centrifugal forces, the attraction from the second body is taken into account in the tidal approximation. The spatial form of equilibrium figures as triaxial ellipsoids is found by an analytical and numerical method. The spin rotation of ellipsoidal equilibrium figures is established to occur not around small axes, as is usually assumed, but around the middle axes of the ellipsoids. This method is used to study the binary asteroid (190166) 2005 UP156, which approximately satisfies the initial conditions of the problem. The study showed that with the parameters known today, the system of two asteroids (190166) 2005 UP156 is nonequilibrium.

This manuscript illustrates the existence, locations, and stability of equilibrium points under the effect of Stokes drag in the restricted four-body problem (R4BP) with variable mass when all the primaries are source of radiation. The motion of the fourth body of negligible mass (infinitesimal mass) is effected by the motion of the primaries, and its motion is perturbed by the radiation pressure and Stokes drag. All the primaries are established at the vertices of an equilateral triangle and known as Lagrangian configuration. The dynamics of an infinitesimal body has been studied under the influences of radiation pressure of all the primaries with Stokes drag and variable mass. Jeans’ law and space time transformations of Meshcherskii have been used to formulate the equations of motion of the infinitesimal body. We have numerically investigated the existence and locations of the equilibrium points in the theoretical ranges of the parameters. The numerical investigations delved that all the equilibrium points are non-collinear, the collinear equilibrium points do not exist due to the presence of Stokes drag. Further, we have observed that all the equilibrium points are unstable for all values of the parameters considered. Moreover, the regions of motion have been drawn for different values of the parameters, i.e., for the radiation parameters ({{q}_{i}} (0 < {{q}_{i}} < 1),) (i = 1,2,3), the proportionality constant (alpha (0 < alpha leqslant 2.2)) occurs due to Jeans’ law, the mass parameter (mu (0 < mu leqslant 1{text{/}}3)), and for the dissipative constant (k (0 < k < 1)). This model has novelty in the sense that we have studied this problem first time by combining the concept of Stokes drag in the restricted four-body problem, considering all primaries as the source of radiation and the fourth body having variable mass. This paper is applicable in various di-sciplines of celestial mechanics as space mission planning, satellite dynamics, and fundamental astrodynamics research. Finally, we have justified the importance of our model by applying it to an appropriate stellar system.

The paper examines the possibilities of using multi-frequency synthesis methods for very long baseline (VLBI) space radio interferometers to improve the ((u,{v})) coverage and the quality of the resulting synthesized images. To evaluate the contribution of multi-frequency synthesis methods, simulations of VLBI observations were performed using the example of the space VLBI concept that is based on a combination of circular near-Earth orbits.

High-resolution optical spectra of the B[e] star CI Cam were obtained on arbitrary dates 2002–2023 using the 6-meter BTA telescope with the echelle spectrograph NES. The variability over time of the powerful emissions of H_α and He I profiles is found. For two-peak emissions with “rectangular” profiles, the intensity ratio of blue-shifted and red-shifted peaks is ({text{V/R}} geqslant 1), except one date. A decrease in the intensity of all double-peaked emissions with “rectangular” profiles was revealed as they moved away in time from the 1998 outburst. The average radial velocity for emissions of this type for all observation dates varies in the range ({{V}_{r}}({text{emis}}{-} d) = ) ( - (50.8 {div} 55.7) pm 0.2) km/s. The half-amplitude of the change (standard deviation) is equal to (Delta {{V}_{r}} = 2.5) km/s. The velocity for single-peaked ion emissions (Si III, Al III, Fe III) differs little from the values of ({{V}_{r}}({text{emis}}{-} d)), but the measurement accuracy for these emissions is worse: the average error for different dates ranges from 0.4 to 1.3 km/s. The systemic velocity is assumed to be ({{V}_{{{text{sys}}}}} = - 55.4 pm 0.6) km/s according to the stable position of the forbidden emission [N II] 5755 Å. The position of single-peak emissions [O III] 4959 and 5007 Å is also stable: ({{V}_{r}}([{text{O}};{text{III}}]) = ) ( - 54.2 pm 0.4) km/s. Emissions [O I] 5577, 6300, 6363 Å, [Ca II] 7291 and 7324 Å are absent from the spectra. Appearance of the emission near 4686 Å is an infrequent event, its intensity rarely exceeds the noise level. Only a wide asymmetric emission with an intensity of about 16% above the continuum was registered in the spectrum for September 3, 2015. Questions arise about the use of this emission to estimate the period of variability of the star and about localization of this feature in the CI Cam system. The photospheric absorptions of N II, S II, and Fe III with a variable position are identified.

The results of new photometric observations of the chromospherically active star ET Dra, performed using telescopes of the Zvenigorod INASAN Observatory, the Russian-Cuban Observatory in the territory of the Republic of Cuba (Havana), and the Terskol INASAN Observatory (a total of 8 sets of observations) with the addition of archival observations of the Kamogata Wide-field Survey. Variations in the shape of the light curve caused by the rotational modulation of a star with spots on the surface, as well as studies of the long-term variability of the star’s brightness, were investigated based on the data acquired in 2018–2023. Characteristic changes in the ET Dra light curve were noted including a decrease of the stellar brightness in the (V) filter, its cyclic variations, and subsequent brightness increase. The shape of the phase curve and the duration of the extended minimum of brightness vary. During the HJD 245 9670–245 9715 interval, the amplitude of the star’s brightness variability reached a maximum value of more than 0.4^m, as it was in 1990. The surface temperature inhomogeneities maps were calculated and estimates of the spottedness parameter S of the object were performed for each of the 8 sets of observations. Maximum value of parameter S was 32.2‒33.5%. Based on the constructed power spectra, the values of possible cycles of long-term activity of the star were obtained as 570 and 1160^d (1.56 and 3.18 years, respectively).

The paper presents the method for detecting exoplanets in the image archive obtained by telescopes of the MASTER Global Network since 2002. The unique archive represents homogeneous photometric data obtained over 20 years for the northern (MASTER-Amur, MASTER-Tunka, MASTER-Kislovodsk, M-ASTER-Tavrida, MASTER-IAC, MASTER-OAGH) and 11 years for the southern sky (MASTER-OAFA, MASTER-SAAO). Algorithm of gamma-ray burst error box observation on the MASTER wide-field telescopes make it possible to detect transit phenomena and find exoplanets in archival data. The article presents the results of a photometric analysis of the TESS exoplanet candidate TOI–3570.01.

A new model of a force-free magnetic flux rope with a high concentration of electric current on the axis is presented. The general property of axisymmetric force-free magnetic ropes is that with the exit of the top of the magnetic loop-rope into the corona, the external pressure that keeps it from lateral expansion steadily decreases, and with some critical decrease in this pressure, the longitudinal magnetic field of the rope becomes zero on the surface where the electric current changes its sign (it is current inversion surface—CIS). In this case, the force-free parameter (alpha (r)) and the azimuthal electric current j_ϕ(r) experience a second-order discontinuity on this surface, so that in the vicinity of CIS their values begin to increase without limit. The current (drift) speed of electrons here will inevitably exceed the speed of ion sound. This serves as a trigger for the heating of non-isothermal plasma (so it turns out T_e ( gg ) T_i) and the excitation of plasma ion-acoustic instability of the plasma not only near the CIS, but also in the central region of the rope, on its axis, where the current density is especially high. The appearance of anomalous resistance leads to rapid dissipation of the magnetic field and the generation of a super-Dreicer electric field. The Parker effect, associated with the equalization (with some delay) of the torque along the axis of the rope due to the transfer of the azimuthal field to the region of energy release, leads to quasiperiodic pulsations of hard flare radiation and, ultimately, ensures the flare release of the most part of free magnetic energy accumulated in the rope.

We provide an analytic review of problems of the modern stellar astronomy. It mostly based on talks presented at the thirteenth annual conference on Modern Stellar Astronomy, held in Volgograd State University (Russia) in May 2023.

Temporal structure of the average rotation measure and the evolution of energetic characteristics of accretion disk in a shearing box approximation are considered. The temporal structure of rotation measure consists of both low- and high-frequency alternating sign oscillations. The mechanisms responsible for these oscillations and their connection with the disk dynamo are discussed. The 2D distributions and the vertical structure of rotation measure and magnetic energy are analysed for times corresponding to extrema and close to zero values of rotation measure. It is shown that the extrema of rotation measure are formed on account of several individual turbulent structures with large amplitudes that are related to magnetorotational and Parker instabilities. It is found that the spatial locations of these structures correspond to areas with high local magnetic energy. The possibility of estimating the period of disk dynamo using measurements of rotation measure is discussed. Cases of Sgr A* and M87* are considered.

The article is devoted to the analysis of the evolutionary status of the X-ray binary stars of the Galaxy. It is shown that the assumption of the conservative evolution of these binary systems leads to an overestimation of the X-ray luminosity of the Galaxy by 3–4 orders. The total observed rate of accretion of matter by relativistic components of X-ray binaries is close to ( {sim} {{10}^{{ - 6}}}{{M}_{ odot }}{text{/}})yr, while the theoretically possible rate reaches ( {sim} {{10}^{{ - 2}}}{{M}_{ odot }}{text{/}})yr. The contradiction between these estimates is eliminated if two factors are taken into account. The first of them is the formation of a common envelope in massive X-ray binary systems after filling the Roche lobe by the donor and the brief phase of a bright X-ray source. The common envelope eliminates the output of X-ray radiation generated during accretion, and also leads to the loss of part of the donor’s matter from the system. The second factor is the presence of intense stellar wind of donors in massive X-ray binary, as well as the occurrence of induced stellar wind in low-mass donors due to exposure to hard radiation from an accreting relativistic star. At the same time, the generally accepted assumption that donors of X-ray binaries fill their Roche lobes may not be fulfilled. A significant part of the donor’s wind matter may be lost from the system. In addition, radiation can enhance the stellar wind of the accretion disk, and part of this wind will also leave the system. There are other factors that reduce the total number of accreted matter: supernova explosions in X-ray binaries, destroying part of these systems, the impossibility of accretion onto rapidly rotating young neutron stars with a strong magnetic field, as well as a rapid drop in the rate of loss of matter by the donor as its mass decreases, characteristic for low-mass X-ray systems.