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Volume 102, Nº 6 (2025)
Articles
Entropic Cosmology Based on Kaniadakis Dual Entropy on the Cosmological Horizon of the Universe
Resumo
Within the framework of entropic cosmology, several variants of the model of the Universe evolution based on the Friedman-Robertson-Walker (FRW) equation system are considered, reconstructed taking into account a new modification of the Kaniadakis entropy at the cosmological horizon. The modification is carried out by replacing the Bekenstein-Hocking entropy in the dual expression of the Kaniadakis entropy (in which all states have the same probability) by the Barrow entropy associated with the transformation of the horizon of the Universe surface due to quantum-gravitational effects. As a result, various cosmological scenarios of the accelerated expansion of the Universe on the basis of the reconstructed FRW equations containing an additional force term depending on two free parameters of the model are obtained: the deformation parameter of the Kaniadakis entropy, which is responsible for taking into account the peculiarities of space-time, due to the long-range nature of gravitation, and the deformation parameter of the Barrow entropy, which is responsible for the fractal structure of the cosmological horizon surface, associated with the action of gravitational-quantum effects. The presence of two free parameters allows us to obtain new variants of driving forces in the FRW equations, which cause a deviation from the ‘standard’ Bekenstein-Hawking holographic model and thus lead to a more accurate approximation to reality. The proposed approach meets the known requirements for thermodynamic modelling of the dynamical evolution of the Universe without involving the concept of hypothetical dark energy and based on the use of anti-gravity entropic forces. The obtained results show that the proposed entropic formalism can open additional opportunities for deeper insight into the nature of space-time and fractal properties of the Universe horizon.
Astronomičeskij žurnal. 2025;102(6):449-467
449-467
Gas-dynamic instabilities in a two-dimensional boundary layer during accretion
Resumo
The purpose of the work is to build a self-consistent gas-dynamic model of the accretion disk of a compact astrophysical object, taking into account viscosity. The matter falling on a compact object consists of proton gas, electrons, and radiation arising from the braking of a rotating gas at a speed comparable to light. Physical proton viscosity is not enough in the gas-dynamic accretion model with laminar flow. It is necessary to introduce the so-called turbulent viscosity, probably arising from the development of instabilities, to explain the loss of the disk angular momentum. With a quantitative mathematical model of gas dynamics, taking into account the generally accepted turbulent viscosity, we want to demonstrate a solution with such instability. In a recently published work on Kepler disk braking, we were able to obtain only large-scale vortex structures arising from azimuthal perturbations, for example, due to tidal effects, and demonstrated an increase in disk braking against a neutron star due to these vortex structures. And the development of small-scale shear instability on the surface of a neutron star for a Kepler disk was not demonstrated in calculations. In this work, we examine a non-Keplerian disk with a non-zero negative radial velocity, ensuring the flow of matter to the surface of a compact star, as a result of which shear instability and turbulence appear.
Astronomičeskij žurnal. 2025;102(6):468-479
468-479
Parameterisation of m-giants from WBVR and ugriz photometry data
Resumo
The slope of the late giants sequence in some two-colour diagrams differs significantly from the slope of other sequences and from the slope of the interstellar reddening lines. This circumstance makes M giants an indispensable source of data on both stellar parameters and interstellar extinction. The aim of the present study is to find suitable two-colour diagrams for the parameterisation of M-giants and to develop a parameterisation technique from the observed photometry. The work results in a tool for determining the intrinsic colour, spectral type and interstellar extinction parameters for the WBVR and ugriz photometric systems. The work is partially based on a talk presented at the Modern Stellar Astronomy 2024 conference.
Astronomičeskij žurnal. 2025;102(6):480-489
480-489
Detection of radio emission from magnetar RX J1605.3+3249 at frequency 111 MHz
Resumo
For the first time, pulsed radio emission from the magnetar RX J1605.3+3249, which is part of the “magnificent seven”, has been detected. Data obtained at the BSA LPI radio telescope at a frequency of 111 MHz in the period from 2012 to 2024 were processed. The peak flux density mJy and the dispersion measure pc/cm3 were measured.
Astronomičeskij žurnal. 2025;102(6):490-495
490-495
Analysis of Data on the Characteristics of the Most Powerful Discrete Radio Sources Used in Measurements of the Gain of Large Antennas by Radio Astronomy
Resumo
For the effective application of the radio astronomical method for measuring the gain of large antennas, the problems of discrepancies in the flux densities of the main calibration radio sources (supernova remnants Cassiopeia A and Taurus A and the radio galaxy Cygnus A) according to data from different catalogues are analyzed, as well as taking into account their angular sizes and structure. A comparison of the data on the characteristics of these radio sources obtained at the Nizhny Novgorod Research Institute and other radio astronomical observatories over several decades is carried out.
Astronomičeskij žurnal. 2025;102(6):496-508
496-508
Spottedness and Flare Activity of Solar-Type Stars with Exoplanets
Resumo
On the base of the lists of objects from the archives of the LAMOST survey telescope and the TESS, Kepler and K2 space missions we study the manifestations of the spot activity of solar-type stars with exoplanets with pronounced flare activity. Diagrams of the form {spottedness parameter Sflare energy} and {spottedness parameter S-rotation period} are considered. As in the case of solar-type stars with superflares and other active stars among the objects under consideration the most active ones rotate faster, they are younger and the area of spots on their surface is greater. The difference is that the spottedness of most stars with planetary systems does not reach the maximum values of the spottedness parameter for stars with superflares. Among the 6 objects with the light curves available in the TESS mission archive the solar-type star TIC 410214986 (DS Tuc) with pronounced photospheric and chromospheric activity which is a member of the Tucana-Horologium group with an age of about 45 million years attracts special attention.
Astronomičeskij žurnal. 2025;102(6):509-514
509-514
Rayleigh laser guide star for the Zeiss-2000 telescope at the “Terskol Peak” observatory
Resumo
This paper describes the design and technical features of the Rayleigh laser guide star (LGS) system as a reference source of an adaptive optical system developed for use on the Zeiss-2000 telescope of the Terskol Peak Astronomical Observatory (coordinates 43°16’34”, 42°29’57”). Experiments were performed on the Zeiss-2000 telescope to test the developed system. As a result, a signal was received from the LGS sufficient for the operation of the wavefront sensor. The presented numerical estimates of the effectiveness of adaptive correction from the Rayleigh LGS show that in the future, the use of an adaptive optical system on this telescope will significantly improve the quality of the generated image by increasing the Strehl ratio by at least ten times.
Astronomičeskij žurnal. 2025;102(6):515-523
515-523
524-524