Astronomy Reports

The formation of large-scale structures in the universe is investigated using a pressureless medium model. The evolution of initial perturbations and the formation of singularities, such as delta density functions, are considered within the framework of the Euler-Poisson equations for isobaric media. It is shown that different initial conditions lead to the emergence of different types of features, including point and curved ones. Criteria for the formation of features depending on the initial conditions are proposed.

In 2021-2022, photometric observations were carried out in the Ic filter of the faint X-ray nova in a quiescent state GS 2000+25 (QZ Vul). Compared to 1995-1999, no significant long-term changes in the orbital period were detected, nor were there any changes in the average brightness of the system, the amplitude, and the shape of the orbital light curve. The average Ic-light curve of the system (the total amplitude A ~0.3^m) is constructed. The shape of the curve corresponds to the effect of ellipticity with a negligible effect of X-ray heating of the star and with a small difference in the heights of the maxima. The main contribution to the total flux from the system in the Ic filter is made by the secondary component K3 V-K6 V (81-87%). The contribution of the radiation from the disk with a hot spot is ~10-14%. An interpretation of the Ic mean light curve of QZ Vul is performed within the framework of a model of a close binary system consisting of an optical K4.5 V star that completely fills its Roche lobe and a compact (relativistic) object surrounded by a weakly elliptical accretion disk of complex shape, thin near the boundary layer, and with a thick outer edge. The presence of a gas flow (hot line) and a hot spot on the lateral surface of the disk is taken into account. Based on the dependences of the residuals χ² on the mass ratio q and on the inclination of the orbit i at a significance level of 5%, confidence intervals were obtained for q (q = 26.2-30.4, q_min = M_x/M_v = 28) and i (i = 61°-66°, i_min = 64°). The masses of the stars in the system are estimated based on the mass function of the optical star. The mass of the black hole is M_x = (6.8-8.2)M_⊙ with the optimal value of 7.34M_⊙. The mass of the optical star lies in the range of (0.21-0.34)M_⊙ with the optimal value of 0.265M_⊙. The radius of the optical star K4.5 V is ∼0.64R_⊙. Its mass, radius, and spectral type are inconsistent with the data for main-sequence stars and correspond to an evolved star that has lost part of its mass during a long-term mass exchange in the system.

A method for pulsar timing based on monitoring data from the 3-th beam of the Large Phase Array (LPA LPI) radio telescope is proposed. In our observations, recorders with quartz clock generators were used as local clocks. Such recorders initially had an accuracy and hardware reference to the UTC time scale insufficient for pulsar timing. We have developed a method for referencing such clocks to the UTC based on observations of known pulsars used as intermediate reference clocks. This allowed us to improve dramatically the accuracy of determining the Time of Arrivals (TOA) of pulsars’ pulses. We applied this method to the results of our observations of 24 second period pulsars over a time interval of 10 years. It was shown that the accuracy of the pulsar period, its first derivative (P and Ṗ) and their coordinates in right ascension and declination (α, δ) allow us to predict the pulsar phase within ±0.5P during several years. The accuracy of determining the coordinates by right ascension and declination was typically better than 10ʺ with an angular resolution of the radio telescope of about 30ʹ. That makes it possible to use these parameters for timing using radio telescopes with narrow beam patterns. The accuracy of the calculated period was typically better than 10^–8 s.

Refined and improved the previous approximate method to correct selection effects in observing exoplanets by radial velocity technique, which caused a significant error in the low-mass region. Lomb-Scargle periodograms were used to take into account the different number of radial velocity measurements of the host stars. We showed that in the region of 2–14 Earth masses, the distribution of planets discovered by the radial velocity technique follows a power law with an exponent of –1: dN/dm~m^{^}(-1).

All three orbits for doubly eclipsing system (2+2) BU CMi were significantly refined using new TESS data and published spectral observations. New values of apsidal motion and accurate physical parameters of the system are obtained. Component A: T₁ = 9860 ± 50 K, M₁ = (2.7 ± 0.15)M_⊙, R₁ = (2.19 ± 0.07)R_⊙, T₂ = 10000 ± 80 K, M₂ = (2.7 ± 0.15)M_⊙, R₂ = (2.23 ± 0.07)R_⊙, apsidal period P_aps = 25.06 yrs. Component B: T₁ = 10260 ± 80 K, M₁ = (2.7 ± 0.15)M_⊙, R₁ = (2.33 ± 0.02)R_⊙, T₂ = 9700 ± 50 K, M₂ = (2.5 ± 0.15)M_⊙, R₂ = (2.04 ± 0.02)R_⊙, P_aps = 25.22 yrs. Orbiting period P_orb = (5.88 ± 0.03) yrs. Photometric parallax exactly equals Gaia DR3 value π = 0.00401ʺ. The age of the system is determined to be 224 million years at solar chemical composition. The work is partially based on a talk presented at the Modern Stellar Astronomy 2025 conference.

A statistical analysis of survey observations conducted by the global network of MASTER robotic telescopes over 20 years has been used to derive independent constraints on the optical emission associated with Fast Radio Bursts (FRBs). The method is based on simulating a synthetic catalog of FRBs, uniformly distributed across the sky and in time, and subsequently checking for the absence of random coincidences with optical observations. As a result, a constraint on the ratio of the burst energy in the optical band to the energy in the radio band has been obtained, η = 4.5 × 10⁴. Although this limit is less strict than that provided by the GAIA mission, it offers an independent test for FRB origin models and is less dependent on assumptions about the duration of the optical signal. The results place important constraints on theoretical models that predict significant optical emission from FRBs.

Since 2017, Institute of Astronomy of the Russian Academy of Sciences (INASAN) has been engaged in a collaborative effort with the Institute of Geophysics and Astronomy of the Republic of Cuba (IGA). During this period, an optical observation station of the international Russian-Cuban Observatory (RCO) was established on the premises of the IGA in Havana. This station is equipped with a robotic 20-cm wide-field telescope. Observations are conducted remotely in a collaborative mode by Russian and Cuban astronomers. In 2024, the Russian segment of the RCO was established at the Kislovodsk Observatory of INASAN. The optical station includes a 50-cm telescope fitted with an astronomical camera for photometric observations and a medium-resolution spectrograph. Observations are carried out jointly by Russian and Cuban astronomers via remote access. This paper provides a description of the optical complex’s equipment and presents the initial results of its operation in 2025.