bluuebunny/crossref_metadata_2025 huggingface dataset:
Влияние версии библиотеки TensorFlow на качество генерации кода по изображению
Authors: Никитин И.В.
Published: December 2024

Данное исследование представляет собой сравнение эффективности обучения моделей, реализующих два разных подхода: усложнение исходной архитектуры нейронной сети либо же сохранение архитектуры при улучшении инструментов, которые используются в основе обучения. Попытки усложнения архитектуры решения по генерации исходного кода на основе изображения приводят к сложно поддерживаемым в будущем решениям. При этом подобные улучшения никак не используют более современные инструменты и библиотеки, на основе которых такие системы построены. Актуальность исследования обусловлена отсутствием попыток использования более современных и актуальных библиотек. В связи с этим, в ходе эксперимента по сравнению показателей моделей трех вариантов систем по генерации исходного кода на основе изображения: оригинальной системы pix2code, ее усложненного варианта и варианта с актуальной версией библиотеки TensorFlow – в процессе их обучения было выявлено, что подходы с усложненной архитектурой и актуальной TensorFlow обладают одинаковыми показателями, более качественными, чем оригинальная pix2code. На основе проведенного эксперимента можно сделать вывод о том, что актуализация библиотеки TensorFlow может дать дополнительный прирост в качестве результатов, которые может предсказывать система по генерации исходного кода на основе изображения.

This study compares the efficiency of training models that implement two different approaches: complicating the original neural network architecture, or maintaining the architecture while improving the tools used in the training framework. Attempts to complicate the architecture of the solution for generating source code based on an image lead to solutions that might be difficult to support in the future. At the same time, such improvements do not use more modern tools and libraries that such systems are built upon. The relevance of the study is due to the lack of attempts to use more modern and relevant libraries. In this regard, during the experiment to compare the indicators of models of three versions of image-based source code generation systems: the original pix2code system, its complex version, and the version with a modern version of the TensorFlow library - in the process of their training, it was revealed that approaches with a complex architecture and the current TensorFlow have the same indicators, higher quality than the original pix2code. Based on the experiment, we can conclude that updating the TensorFlow library can provide an additional increase in the quality of results that the image-based source code generation system can predict.
Observations of giant pulses from B0531+21 at the Institute of Applied Astronomy
Authors: Bezrukov I. , Gayazov I. , Dyakov A. , Ivanov D. , Ipatov A. , Kurdyubov S. , Marshalov D. , Melnikov A. , Mikhaylov A. , Olifirov V. , Rakhimov I.
Published: December 2024

This paper presents the results of observations of giant pulses from the pulsar B0531+21 (the Crab Nebula pulsar) conducted at the Institute of Applied Astronomy of the Russian Academy of Sciences (RAS). The primary aim of the study was to establish a domestic monitoring service and compute the ephemerides for this pulsar. Observations commenced in mid-2023 using the RT-13 telescopes of the Quasar-KVO network, operating in the S, X, and Ka bands. To achieve the research goals, we utilized the VLBI (Very-Long-Baseline Interferometry) registration system along with specially developed software and algorithms for data processing. A monitoring service for giant pulses was created, providing weekly ephemerides of the pulsar for over one and a half years. The period and its derivative were determined separately by timing the main pulses and interpulses. The obtained results demonstrate a high accuracy of period determination, consistent with the data from the Jodrell Bank Observatory
, with a root mean square deviation of 7 picoseconds.
The results of simultaneous TESS and multiband photometric observations of BL Lac during a high activity
Authors: Gorbachev M. , Butuzova M. , Pit N. , Krivenko A.
Published: December 2024

For the blazar BL Lac, we analyze data from TESS and multiband observations that were obtained using the MTM-500 telescope of the Crimean Astrophysical Observatory from 1.09.2022 to 30.09.2022.
During this period, BL Lac showed strong variability, both accompanied and unaccompanied by changes in spectral index.
The shortest characteristic variability times are mainly in the range from 0.2 to 1 day and do not depend on the object brightness, the spectral index, and the average amplitude of the variability within the corresponding intervals of the light curve.
It indicates that the mechanisms of short-term variability are characterized by two or more independent parameters.
Search for proton jets in blasars as possible emitters of high-energy neutrinos
Authors: Kovalev Yu. , Zhekanis G. , Kovalev Yu. , Sotnikova Yu. , Troitsky S. , Popkov A. , Plavin A. , Erkenov A. , Mingaliev M. , Nizhelsky N. , Tsybulev P. , Bursov N.
Published: December 2024

We continue the RATAN-600 observations of instantaneous 1-22 GHz spectra of active galactic nuclei at 5-7 frequencies in 1997-2024. The main task is the analysis of the results including the CATS database for data beyond 1-22 GHz and the Hedgehog model proposed by N. S. Kardashev in 1969. The new goal is to study the physical parameters of jets in VLBI-blazars and search for compact bright strong variable proton jets as possible sources of high-energy neutrinos in proton-proton and proton-photon processes. Main results of estimating values for magnetic fields, brightness temperatures and angular sizes of both proton and electron jets in 9 blasars are presented. This allows to explain the RadioAstron extra-high brightness temperatures and magnetic fields as well as extremely compact cores in radio jets and to link proton sources of high-energy neutrinos with some radio jets.
The flaring activity of microquasars is the key to understanding the processes of accretion and generation of jet emission
Authors: Trushkin S. , Shevchenko A. , Bursov N. , Nizhelskij N. , Tsybulev P.
Published: December 2024

We present a study of the flaring radio variability of four microquasars during last ten years with RATAN-600. The main aim of researches is a study of the daily light curves at seven frequencies of 1.2-30 GHz and in multi-azimuthal (MA) mode, when for 5h the fluxes are measured every 5-10 minutes at 4.7 and 8.2 GHz. In SS 433 dozens of bright flares were detected over last ten years. The brightest flare (5.5 Jy at 2.3 GHz) in the total history of GRS 1915+105 research occured in August 2023. In 2024 we have detected five giant radio flares in Cyg X-3 during hypersoft-to-hard X-ray states transits. These flares reached fluxes of 13-18 Jy and have similar properties: optically thick phase in the spectra in the beginning of a flare and the exponential fading for 5-30 days. We relate these events with an efficient formation of relativistic jets during the accretion of matter from a normal star. In the Gamma-ray binary LSI+61d303 with regular flares every 26.5 days, we have detected second period of 26.93 days that can be precession period of jets. We find a clear similarity of bright flares in microquasars.
Multi-band variability of the blazar AO 0235+164
Authors: Vlasyuk Valery , Sotnikova Yu. , Volvach A. , Mufakharov T. , Kovalev Yu. , Spiridonova O. , Khabibullina M. , Kovalev Yu. , Mikhailov A. , Stolyarov V. , Kudryavtsev D. , Mingaliev M. , Semenova T. , Kudryashova A. , Bursov N. , Trushkin S. , Popkov A. , Erkenov A. , Rakhimov I. , Kharinov M. , Gurwell M. , Tsybulev P. , Moskvitin A. , Fatkhullin T. , Emelianov E. , Arshinova A. , Iuzhanina K. , Andreeva T. , Volvach L.
Published: December 2024

We present a study of the multiwavelength (MW) variability of the blazar AO 0235+164 based on the radio-to-$\gamma$-ray data covering a period from 1997 to 2023. The radio data are represented by the measurements from the SAO RAS, IAA RAS, and CrAO RAS telescopes. The optical measurements were collected with the SAO RAS 1-m and 0.5-m reflectors. The archive data at 230 GHz from the Submillimeter Array and the $\gamma$-ray data from the Fermi-LAT mission were used too. A significant correlation between different spectral bands is found with time delays up to 1.7 years. The relation between time delay and frequency is well described by a linear law. The revealed features of MW variability for the quiet period and for flaring states suggest that the mechanisms dominating the radio-$\gamma$-ray variations are not substantially different. AO 0235+164 shows a total variability period of $\sim$6 years for all wavelength bands, and 1.4-2.3 years during the low state, which may reflect its general properties.
Classification of jets inactive galactic nuclei
Authors: Zagorulia D. , Lisakov M.
Published: December 2024

This work explores the application of machine learning techniques to classifying jetted active galactic nuclei (AGN) based on Very-Long-Baseline Interferometry (VLBI) observations at frequencies 1-90 GHz. Building upon previous work by Fanaroff and Riley, who classified relativistic jets in radio galaxies on kiloparsec scales, we extend this classification to parsec scales, closer to the central supermassive black hole. This approach enables detailed study of jet spatial structures and can help enhancing accuracy in global positioning systems. We define four morphological classes: single Gaussian source, double Gaussian source, and sources with single or double-sided jets. Synthetic models of AGN jets were generated to create a training dataset for a convolutional neural network (CNN). The CNN was trained on these synthetic data and subsequently applied to classify 130 thousand AGN jet images from the Astrogeo database. The distribution of images into designated classes, predicted by CNN, qualitatively matches the expected outcome.
The evolution of fields in the process of preheating in the early Universe
Authors: Arkhipova N. , Fedorov N.
Published: December 2024

The long-term evolution of fields on the stage of primary heating of the Universe after inflation is investigated. Preheating is the stage of evolution of the Universe at which the inflaton, after the stage of slow rolling down on inflation, begins to oscillate near the minimum of its potential energy and act as a compelling external force in the equations of motion of other fields that were in a quantum state with a relatively small amplitude on inflation. Numerical calculations of the system's dynamics for long times shows that during the early phase of preheating, the energy of the material field is due to parametric resonance it grows to the energy of the inflaton. However, after a considerable duration, when the energies of the fields become aligned and there is a multiple transfer of energy from one field to another, the energy of the material field decreases faster than the energy of the inflaton. This could suggest that parametric resonance may not be sufficient for the disintegration of the inflaton and pumping its energy into the energy of material fields.
Regular distribution of star formation regions along the spiral arms and rings of disk galaxies
Authors: Gusev A. , Shimanovskaya E.
Published: December 2024

Recent studies have indicated that the spatial regularity in the distribution of young stellar population along the spiral arms and rings of galaxies, which was previously thought to be uncommon, is actually a fairly common occurrence. Spatial regularity has been found in the spiral arms and rings of galaxies with different morphologies, from lenticular to extremely late-type spiral. The characteristic regularity scale is equal to 350–500 pc or a multiple of that in all the galaxies studied. Theoretical models suggest a scale of instability for the stellar-gas disk around a few kpc, which is larger than what has been observed. Recent magneto-hydrodynamic simulations, however, indicate the formation of regular chains of star formation regions in spiral arms on a scale of 500–700 pc for galaxies similar to the Milky Way. Modern high-quality surveys, like PHANGS–MUSE, provide the necessary observational data (surface densities and velocity dispersions of gas and stellar population) to directly calculate the regularity scales in galaxies, with high spatial resolution and a wide field of view, which is a promising direction for research in this field.
Spectral study of peculiar galaxies
Authors: Karataeva G. , Merkulova O.
Published: December 2024

A study of five peculiar galaxies (SPRC-69, 0.25cmSPRC-100, 0.25cmSPRC-260, SPRC-269, and SPRC-136) from the new catalog of polar ring galaxies (Sloan-based Polar Ring Catalog, SPRC). Panoramic (3D) spectral data were obtained with the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences with the using the Fabry–Perot interferometer. The large-scale velocity fields, velocity dispersion fields, and monochromatic images of objects in the H emission line were analyzed in detail. All galaxies showed the complex structure and kinematics of their gaseous components. The ``tilted-ring'' method was used to analyze the velocity fields. It was concluded that all the objects studied belong to are classical polar ring galaxies, with the exception of SPRC-100.
Retrograde fall of intergalactic gas onto the S-galaxy: polar rings and activity of galactic nuclei
Authors: Khrapov S. , Khoperskov A. , Khrapov N.
Published: December 2024

The dynamics of intergalactic gas accretion in a gas-rich spiral galaxy has been studied. We use numerical simulations to determine the conditions that lead to the formation of counter-rotating stellar and gas components within the galaxy and promote the influx of gas into the central part of the galaxy with a radius of less than one kiloparsec. The focus is on the dynamic interaction between the intergalactic flow and the gas-rich disc galaxy. The study of the mechanism by which gas is supplied to the central region to fuel the activity of galactic nuclei is a critical part of our work. The retrograde fall of the gas forms a massive, concentrated gas halo at the center of the galaxy, which may provide fuel for the activity of galactic nuclei. An angle of incidence of the gas flow of about 20 degrees to the galactic plane is the most effective and provides maximum gas concentration. Deviations from this angle lead to a decrease in the velocity of the gas flow into the galactic center. The prograde infall of intergalactic gas is incapable of cardinal disruption of the disc and does not result in an effective inflow of gas within 1 kpc radius. This accretion mode provides 100 times less gas mass within the 1 kpc radius compared to retrograde infall. An important additional result of retrograde accretion is the appearance of rotating gas rings at the periphery of the galaxy, which are mainly formed by falling intergalactic gas. The inclination of these rings with respect to the galactic plane varies widely, from 10 to 90 degrees, and depends on the angle of incidence of the intergalactic gas. The numerical simulations of counter-rotating stellar-gas discs cover all stages of the interaction with the falling intergalactic flow over a period of about 7 billion years.
Estimation of the Hubble constant from the scatter of the fundamental plane distances of groups and clusters of galaxies ($71.1\pm 2.8$ km s$^{-1}$ Mpc$^{-1}$)
Authors: Kopylova F. , Kopylov A.
Published: December 2024

To determine the peculiar velocities of galaxy clusters relative to the Hubble Flow, we need to measure the distances of galaxy systems using some method that is sensitive to their distances. The fundamental plane (FP) of early-type galaxies is one such method and is widely used for such problems. Using the FP, we determined the angular distances of 140 groups and galaxy clusters in the local Universe ($z<$ 0.15) and constructed a Hubble diagram between distances and radial velocities in the CMB reference frame in the framework of the flat $\Lambda$CDM model ($\Omega_{\rm m}=0.3$, $H_0=70$ km s$^{-1}$ Mpc$^{-1}$). We obtained the average deviation of the relative distances $\gamma$ from the Hubble dependence for this model $<\Delta \gamma>$=$-0.0066\pm0.0023$ ($N$ = 140). The minimum deviation we found corresponds to the value of the Hubble constant $71.1$ km s$^{-1}$ Mpc$^{-1}$. We found that the logarithmic standard scatter of the relative distances of groups and clusters of galaxies on the Hubble diagram (subtracting peculiar velocities) is $\pm0.0173$ ($N$ = 140), which corresponds to the deviation of the Hubble constant $71.1\pm2.8$ km s$^{-1}$ Mpc$^{-1}$. For a sample of galaxy clusters ($N$ = 63) with X-ray luminosity in the range (0.15–4)$\times10^{44}$ erg/s, we obtained $71.1\pm2.1$ km s$^{-1}$~Mpc$^{-1}$.
Constraints on the population of Galactic objects in the JWST UNCOVER survey catalogue
Authors: Lovyagin N. , Raikov A. , Yershov V.
Published: December 2024

The paper assesses the potential galactic nature of small distant objects (also known as ``little red dots'') in the SUPER galaxy catalogue of the James Webb Space Telescope (JWST) UNCOVER survey. The estimate is based on the assumption that these objects could be brown dwarfs or similar objects with temperatures of a few hundred degrees – if the radiation from the low-temperature bodies was interpreted as the photometric redshift of a typical galaxy. The hypothetical number density of these objects in our galaxy is calculated, such as to match the observed number of ``little red dots'' in the survey. The physical possibility of having this number density in our Galaxy is discarded as contradictory to the dynamical constraints based on the halo mass of our Galaxy estimated elsewhere.
The mass of the Milky Way based on the kinematics of satellites
Authors: Makarov D. , Makarov D. , Makarova L. , Kozyrev K.
Published: December 2024

The Milky Way satellite system is the most studied group of galaxies. Currently, 64 satellites within 260 kpc are known. We have measured high-precision distances, radial and tangential velocities for most of them. We have estimated the total mass of our galaxy to be $M=(7.9\pm2.1)\times10^{11}$ $M_\odot$ using a modification of the projected mass method that takes into account the three-dimensional distribution of galaxies in the group, assuming an isotropic distribution of satellite orbits. The infall of galaxies located outside the virial zone at a distance of 400 kpc allows us to estimate the mass of the system to be of the order of $9\times10^{11}$ $M_\odot$, which is in excellent agreement with the mass inside the virial zone of our Galaxy.
First results of HI survey of recently discovered close dwarf galaxies
Authors: Nazarova A. , Cannon J. , Karachentsev I. , Makarov D. , Chazov M.
Published: December 2024

We describe the results of observations with the 100m Robert C. Byrd Green Bank Telescope (GBT) in the HI line of 54 nearby dwarf galaxies found mainly in the DESI Legacy Imaging Surveys. Of these, we detected 35 galaxies with the following median parameters: the HI-flux of 0.53 Jy km/s, heliocentric velocity of 1123 km/s, and $W_{50}$ line width of 33 km/s. Most of them are isolated irregular objects, and some have turned out to be new probable satellites of nearby disc galaxies: NGC 2787, NGC 3556, NGC 4490, and NGC 5055. The detected galaxies are predominantly gas-rich systems with a median gaseous-mass-to-stellar-mass ratio of 2.41.
Accretion on a wormhole with monopole magnetic field
Authors: Piotrovich M. , Krasnikov S. , Buliga S. , Natsvlishvili T.
Published: December 2024

The presence of even simple magnetized wormholes may have observable consequences. If the wormhole and its surrounding magnetic fields are static, symmetrical, and spherical, and gas in the vicinity falls radially into the wormhole, the resulting spectrum would feature bright cyclotron or synchrotron lines caused by interactions between charged plasma particles and the magnetic field. This radiation would be non-polarized due to the symmetry of the system. The emission of this exotic, non-thermal yet non-polarized type of radiation could serve as a signature for wormholes. Additionally, in this scenario, the formation of an accretion disk is still possible at some distance from the wormhole; however, a monopole magnetic field may complicate this process and lead to the emergence of asymmetrical and one-sided relativistic jets.
Peculiar structure of isolated dwarf galaxy ESO 149–003
Authors: Vladimirova K. , Makarov D. , Chazov M. , Makarova L.
Published: December 2024

The modern deep sky DESI Legacy Surveys allow us to study of extremely low surface brightness structures. Visual inspection of Local Volume galaxies reveals that the dwarf galaxy ESO 149–003 contains shell-like structures that are characteristic of giant elliptical galaxies. This isolated dwarf galaxy, located at a distance of 7 Mpc in the direction of Antivirgo, appears to have absorbed its neighbour. In this paper we analyse the stellar population and star formation history of this galaxy. We estimate the frequency of similar systems by visual inspection of the Local Volume galaxies using images from the Legacy Survey.
About the periodic variation of the stellar magnetic fields
Authors: Bychkov V. , Bychkova L. , Madey J.
Published: December 2024

In this work, a general description of the observed variability of magnetic fields in stars of various spectral types is presented. Average magnetic phase curves (MPC) and their parameters are presented in three catalogs. As a result, there are currently medium magnetic phase curves for 415 stars, 258 of which are Ap/Bp stars. Such a large number of Ap/Bp stars allows you to judge not only the parameters variability, the structure of the global magnetic field, but also opens up the possibility of finding the reason explaining the super slow rotation of some of them.
A nature of the X-ray and optical emission from gamma Cassiopeia stars
Authors: Kholtygin A. , Yakunin I. , Ryspaeva E. , Mokshin D.
Published: December 2024

To test the origin of the X-ray and optical emission from the $\gamma$ Cas-type stars, we analyzed their optical spectra obtained on the 6-m telescope BTA, the 1.25-m telescope of the Crimean station of the State Astronomical Institute (SAI, Moscow), the 2.5-m telescope SAI25 of SAI, and the photometric TESS light curves. We compare the optical variability of the $\gamma$ Cas-type stars with variations of their X-ray luminosity. An overlap between the periods of line profile variations in the spectra of $\gamma$ Cas stars and the variations in their X-ray brightness allows us to assume that a significant fraction of X-rays emits from the same place where the optical radiation comes from. The $\gamma$ Cas-type stars HD 45314, HD 45995 and NGC 6649 9 demonstrate the ultrafast X-ray brightness variations with the periods of about 50–90 seconds, which may be the rotation periods of white dwarfs components of binary systems. Thus, we can assume that at least for these stars the X-ray emission goes partly due to accretion onto rapidly rotating white dwarfs. The anomalously hard X-ray emission from the $\gamma$ Cas stars can be interpreted by assuming that the contribution of non-thermal X-ray emission is generated as a result of a reconnection of the local magnetic field lines of the Be star and its decretion disk.
Dynamics of dust grains and small bodies in accretion disks of young stars with fossil magnetic field
Authors: Kobozeva V. , Khaibrakhmanov S.
Published: December 2024

The paper discusses a numerical model that explores the dynamics of dust particles and small bodies within accretion disks that contain fossil magnetic fields. The model equations include gravitational force, centrifugal force, and drag force depending on particle size and speed. The disk structure is simulated using the magnetohydrodynamic model of Dudorov and Khaibrakhmanov, taking into account the effect of magnetic tensions on gas rotation speed. The dynamics of particles ranging in size from $10^{-4}$ cm to $10^2$ cm in an accretion disk of a typical T Tauri star are modeled. The simulations indicate that the dynamics of particles with a size of 1 m consists in fast sedimentation towards the midplane, followed by a slower radial drift. Sedimentation is accompanied by damped oscillations around the midplane. The slowdown of gas rotation due to magnetic tension leads to an increase in radial drift speed at the disk's periphery. Therefore, the depletion of solid particles in the outer regions of the disks and their accumulation in the ``dead'' zones with weak magnetic fields may occur more rapidly in disks with magnetic fields.
Determination of the dwarf novae parameters and their temporal changes
Authors: Motorina Elizaveta , Shimansky V. , Dudnik A. , Borisov N.
Published: December 2024

We present the development of a method for determining dwarf novae parameters and their temporal changes from the analysis of observations for several times. Using the modeling method of H I lines in the optical spectra of dwarf novae with high-temperature white dwarfs leads to large errors in the measured parameters. Therefore, the idea of using observations for several times was proposed, which will allow to determine the parameters of the system with greater accuracy. The dwarf novae FL Psc, which belongs to the WZ Sge type, was chosen as a test object. Its spectroscopic observations were carried out in 2021 and 2023 years by the 6-m BTA telescope. According to the light curve from the ZTF archive, in 2021 FL Psc was in a quiescent state, and in 2023 observations were made at the final stage FL Psc of relaxation to the pre-outburst level. The values of white dwarf temperature in both times of observations were obtained using the requirement of the invariability of the gravity value on its surface. However, similar temperature values in both times of observations differ from the literature predictions on the temperature increase of a white dwarf after a superoutburst.
Velocities-distance optimization of the rotation model of a homogeneous flat subsystem of Galactic objects:masers
Authors: Nikiforov I. , Sobolev P. , Veselova A.
Published: December 2024

A statistically correct method for optimizing the parameters of the kinematic model for a homogeneous set of Galactic objects has been developed and implemented, which includes minimizing the squares of relative deviations from the observed radial velocity, proper motions, and distant characteristic. The latter refers to the trigonometric parallax (in the case of absolute distances) or the distance modulus (in the case of relative, i.e., photometric, distances). The solution lies in the technique of the principle of maximum likelihood. The presence of measurement errors and natural (dynamic, astrophysical) velocity dispersion is taken into account; the parameters of the latter (velocity ellipsoid) are estimated. The final iterative algorithm includes optimization of the smoothness of the rotation law and a flexible procedure for eliminating outliers in the data, generalized to a four-dimensional field of residuals. The method, without requiring restrictions on the magnitude of random errors in the distant characteristic, directly takes into account the non-Gaussian distribution of errors in heliocentric distances, thereby correcting the corresponding systematic shifts in the parameters of the model and the average rotation curve of the subsystem under consideration. The inclusion of distance uncertainties in the probabilistic model strongly affects the estimates of natural velocity variances (reduces them), and also generally reduces the variances of model parameters. Applying the method to HMSFR maser sources with trigonometric parallaxes gives the following parameter estimates: distance to the center of the Galaxy $R_0 = 7.88 \pm 0.12$ kpc, angular velocity of rotation of the maser subsystem on the solar circle $\omega_0 = 28.43 \pm 0.22$~$\rm km\,s^{-1}\,kpc^{-1}$, corresponding linear velocity $\theta_0 = 224 \pm 4$~$\rm km\,s^{-1}$, the angular velocity of the Sun's rotation around the center of the Galaxy $\omega_\odot = 30.40 \pm 0.20$~$\rm km\,s^{-1}\,kpc^{-1}$.
Fractality and kinetics of the stellar medium in the solar neighborhood based on Gaia DR2 data
Authors: Ostashova M. , Rastorguev A.
Published: December 2024

The fractal nature of the stellar medium in the Solar vicinity has been established by studying 200 000 stars of all spectral types at distances of 1 to 100 parsec from the Sun. The fractal dimension is $D \approx 2.41$. Based on the data obtained, we examine the kinetic properties of the fractal stellar medium in the solar vicinity. We show that kinetic parameters such as correlation length, dynamic friction coefficient, effective interstellar distance for fractal stellar medium differ from the1 corresponding parameters for quasi-homogeneous medium with limited density fluctuations, and depend on the fractal dimension. We find that the fractal structure of the stellar medium leads to a reduction of the relaxation time in our Galaxy.
Quasi-periodic pulsations in flares of UV Ceti-type stars
Authors: Panferov A. , Kolotkov D. , Beskin G. , Karpov S. , Plokhotnichenko V. , Maryeva O.
Published: December 2024

Quasi-periodic pulsations (QPPs) were observed in the light curves of solar and stellar flares. The number of stellar QPP events is quite small (213 in 2021), which is why they are interesting. QPPs can be used to investigate the properties of flare regions and they are still a problem for flare models. QPPs were identified in stellar flares across a wide range of wavelengths, from radio to X-rays. In the optical band they are searched mainly in the Kepler and TESS data. The periods of QPPs detected from these sources are longer (tens of minutes) than from the high cadence data. Observations with the 6-m telescope BTA and the MANIA complex, as well as the space observatory GALEX, reveal QPP periods of only tens of seconds. On the other hand, solar flares are typically weaker (energies $\ll 10^{32}$ erg) than stellar flares, that possibly makes them more difficult to detect in white light. Our data on 157 flares of dM-type stars (EV Lac, Wolf 359, Wolf 424, V577 Mon, and UV Ceti), obtained from 70 hours of observations with the BTA telescope in $U$-band with microsecond time resolution, represents a significant breakthrough in the search for QPPs in stars. In this paper, we present the characteristics of 13 QPPs found in 44 flares. The QPPs have periods ranging from 6 to 107 seconds, and were identified using both Fourier transform and empirical mode decomposition methods. We classify the observed QPPs based on the evolution of their oscillation envelopes and fractional flux amplitudes.
The impact of non-ideality effects in dense plasma on the evolution of white dwarfs
Authors: Podkuichenko D. , Blinnikov S.
Published: December 2024

Recently made possible observations of cool and faint white dwarfs using the Gaia and other telescopes provide rich material for refining the modeling of the final stage of their evolution, which in turn can be used to study the behavior of matter under extreme conditions. In this paper, we simulate the thermal evolution of white dwarfs for different atmospheric compositions using equations of state for non-ideal dense plasma. By taking into account the effects of non-ideality in the code for the evolution of white dwarfs, it is possible to reach the stage of crystallization at the center of the star. The subsequent acceleration of cooling is significant for massive white dwarfs ($M \approx 1.3$ $M_{\odot}$), for which the cooling time at $T_{\rm eff} \approx 3 \times 10^3$ K decreases almost 10 times compared to the calculation without non-ideality effects.
Wolf–Rayet stars mass-loss rates determined from spectroscopic measurements of the orbital evolution for close WR+OB binary systems
Authors: Shaposhnikov I.
Published: December 2024

The most reliable method for estimating the rate of mass-loss by the Wolf–Rayet stars wind is based on the assessment of secular variations in the orbital periods for close binary systems containing such stars, most often WR+OB systems. Previously, almost only photometric observations of well-studied eclipsing close WR+OB binaries were used for these purposes. This report describes the results of the work on the search for mass-loss-induced evolutionary variations in the orbital period for close WR+OB binaries and the mass-loss rates measurements for WR stars in these systems. Orbital period variations were detected in five systems studied: V444 Cyg, CQ Cep, CX Cep, WR 127 (Hen 3-1772), and WR 141 (V2183 Cyg). In addition, phase deviations between the radial velocity curves obtained at different epochs are suspected for the A pair of the GP Cep quadruple system. For eclipsing systems, estimates of the rate of change of the orbital period from the radial velocity curves are in good agreement with the corresponding estimates obtained from the light curves. A secular shortening of the orbital period has been confirmed for the CQ Cep system, which can be explained by the high degree of closeness of this system and the associated mass transfer processes. For the WR 127 and WR 141 systems, dynamic estimates of the change of the orbital period and the rate of mass loss have been obtained for the first time. Estimates of the rate of mass-loss by Wolf-Rayet stars show a power-law dependence on the mass of the star with an exponent of about 2. The effect of the finite size of stars, which turns out to be significant for estimates of the rate of mass loss to the wind in the closest systems, is discussed.
An X-ray study of the dwarf nova candidate OGLE-BLG-DN-0064 using Chandra data
Authors: Sibgatullin A. , Dodon V. , Galiullin I.
Published: December 2024

OGLE-BLG-DN-0064 (hereafter, OGLE-64) has been identified as a possible dwarf nova candidate due to the optical outburst activity recorded by the Optical Gravitational Lensing Experiment (OGLE) survey. We study the X-ray properties of OGLE-64 using the Chandra archival data. OGLE-64 shows an X-ray luminosity of $L_X \approx 1.5 \times 10^{32}$ erg/s in the 0.5–7 keV energy band and a high ratio of X-ray flux to optical flux $F_X/F_{\rm opt} \approx 1.5$. We found no significant optical and X-ray periodicity with the timing analyses. The X-ray spectrum of OGLE-64 can be approximated by a power-law model with a photon index of $\Gamma \approx 1.9$ and an optically thin plasma model with a temperature of $kT \approx 6.4$ keV. The isobaric cooling flow model gives an accretion rate in the system of about $\dot{M}_{\rm acc} \approx 5.4 \times 10^{-11}$ $M_\odot$/yr and the white dwarf mass of $M_{\rm WD} \approx 0.8$ $M_\odot$. The X-ray properties and the optical outburst activity suggest that OGLE-64 is a dwarf nova.
Formation of Be stars in binary systems with conservative mass exchange
Authors: Staritsin E.
Published: December 2024

In the case of conservative mass exchange in a binary system in the Hertzsprung gap, the mass of the accreting star can increase by up to two times. The accreted matter brings Keplerian angular momentum with it. The meridional circulation transfers 80–85% of the incoming angular momentum to the surface of the accretor. The increase in the mass and angular momentum of the accretor occurs due to the loss of this part of the angular momentum. After the mass exchange is completed, most of the angular momentum is concentrated in the accreted layers. The accretor has a large enough angular momentum to maintain its status as a Be star during its subsequent evolution on the main sequence.
A sphere or a disk? Accretion of gas onto isolated stellar-mass black holes
Authors: Zagorulia D. , Beskin G.
Published: December 2024

The most crucial problem in constructing a coherent model of the universe is the behavior of spacetime in the vicinity of the event horizons of black holes (BH). These regions can be accessible to direct observations only at low rates of spherical accretion. Based on the analysis of the current characteristics of interstellar gas turbulence, it has been shown that the spherical mode of accretion, unlike the disk mode, occurs at sufficiently low densities of the medium (excluding clouds and ``hot'' zones). In this case, disks can form only around virtually stationary Kerr and Schwarzschild BHs.
Comparison of the dynamics of coronal holes identified by two detection methods in solar activity cycles 24-25
Authors: Andreeva O.
Published: December 2024

In this study, we analyze for the first time the long-term variations of coronal holes (CHs) identified by two different automatic detection schemes: Spatial Possibilistic Clustering Algorithm (SPoCA) and Convolutional Neural Network (CNN193). The source material was the observational data acquired by the Atmospheric Imaging Assembly instrument onboard the Solar Dynamics Observatory (AIA/SDO) in the Fe XII 19.3 nm line in the period from June 16, 2010, to May 13, 2021. An initial analysis comparing the long-term variations of the CH areas extracted by the SPoCA method and used by us in earlier works to study their evolution at different stages of the 24th and at the beginning of the 25th cycles showed fairly good agreement with the trend of the CH areas identified by the CNN193 algorithm for the same period. Both schemes reveal hemispheric asymmetry in the generation of CHs both in time and in amplitude.
Radio spectroscopy of the solar corona
Authors: Bogod Vladimir , Lebedev M. , Ovchinnikova N. , Ripak A. , Kurochkin E.
Published: December 2024

The presence of continuous cooling and heating processes is a crucial condition that determines the existence of the solar corona. The defining aspects of the corona include the magnetic field, low plasma density, and high temperature of the corona. In this regard, the study of low-contrast structures in optical ranges is limited even with the use of large specialized telescopes. The radio range provides higher sensitivity, which can be used to detect very weak structures of emerging activity. However, the radio astronomical range also faces challenges in observation, both in terms of spatial resolution and the limitations of dynamic range due to the high temperature of the Sun's corona.

Observations show that the use of instruments with a large effective area allows us to overcome the main problem associated with the influence of powerful radiation from the quiet Sun, which amplifies equipment noise. The high sensitivity of the RATAN-600 reflector radio telescope to weak signals in radiation flux was used in the decimeter range for the detection of weak microwave bursts at a level of $10^{-3}$ s.f.u. Research and theoretical developments have shown that microwave bursts are caused by magnetic reconnection, which leads to the generation of accelerated particles that excite plasma waves at the second harmonic of the plasma frequency.

Due to significant changes in the concept of radio spectroscopy, work has begun on creating a series of broadband spectral complexes covering several octaves. The results of the first series of observations using the complex in the range of 1-3 GHz for searching for and studying quasi-periodic pulsations in the solar corona are presented here.

A by-product of these observations was the detection of narrow-band absorption in the frequency range 1560-1665 MHz, near the well-known OH absorption line (1612-1720 MHz).
Asteroid activity: spectral features and probable physical reasons
Authors: Busarev V.
Published: December 2024

Spectral signs of sublimation-driven dust activity of main-belt asteroids with primitive mineralogy (of C, B, F, G, and X types) are considered. The reflectance spectra of active asteroids of primitive types are compared with model ones of a conditionally active C-type asteroid surrounded by a dust exosphere consisting of submicron aggregate particles of different composition. This phenomenon in primitive asteroids may be impact-induced and become subsequently periodic near perihelion if connected with considerable water ice deposits of the asteroids. Significant additional factors influencing the primitive-type active asteroids, although secondary by random nature, are flares and eruptive events on the Sun, and electrostatic field of photoemission nature on the sunlit side of the bodies. We argue that the formation of aggregate dust particles in a dust exosphere of active asteroids may be one of the fundamental processes.
Susceptibility of electromagnetic fields in the Solar System to gravitational wave effects from relativistic binary star systems
Authors: Grunskaya L. , Isakevich V. , Isakevich D.
Published: December 2024

Using an eigenvector and signal component analyzer (eigenoscope), the problem of identifying the impact of gravitational waves of relativistic binary star systems (RBSS) with large and small eccentricity on the vertical component of the electric field strength ($E_\text{z}$) in the Earth's atmospheric surface layer in the infra-low frequency (ILF) range at high harmonics of the EDS circulation frequencies has been solved. The results were obtained using monitoring data at four spatially separated $E_\text{z}$ observation stations. A model is proposed to explain the effect of the gravitational wave influence of relativistic binary star systems on the vertical component of the Earth's electric field strength in the surface layer of the atmosphere, previously discovered by the authors. The model considers as the mechanism the disturbance of the Earth's orbit by gravitational waves from relativistic binary star systems, leading to small displacements of the Earth relative to the free space charge in the troposphere. The estimates of the amplitude of the $E_\text{z}$ components, spectrally localized at the frequencies of gravitational waves of relativistic binary star systems, obtained on the basis of the presented model do not contradict the experimental results.
Multi-wavelength observations of the impulsive C2.8 class flare producing photospheric impact at the penumbra region of the leading sunspot in NOAA 13256
Authors: Koynash G. , Sharykin I. , Zimovets I. , Ivanov E. , Kiselev V. , Nizamov B.
Published: December 2024

We present the results of a study of the non-eruptive C2.8 class flare in the active region (AR) NOAA 13256, which occurred on March 19,2023 from 02:12 to 02:19 UTC. This event was chosen on the basis of the test launches of the Irkutsk Solar Radio Spectropolarimeter (SOLARSPEL), Badary (ISTP RAS). Despite the low X-ray class and short duration, according to SOLARSPEL data, this impulsive flare had a complex multi-peak fine time structure, recorded at different frequencies in the microwave range. The presence of a photospheric disturbance in the vicinity of the sunspot penumbra, recorded using HMI/SDO, was of great interest for physics and motivated this study. There are few detailed multi-wavelength studies in the literature of low-power flares accompanied by a response at the photosphere level. Notably, this event was observed simultaneously by four X-ray instruments: SoLO/STIX, ASO-S/HXI, FERMI/GBM, and Konus-Wind. As a result, the unique observation conditions of this flare, from the point of view of the available instruments and various recorded physical high-energy processes, motivated us to carry out detailed research. We found that the photospheric perturbations are mostly associated with the stronger magnetic field in the penumbra rather than with the distribution of the HXR sources. The observed flare ribbons were located in the penumbral PIL region, which revealed the complexity of the larger events in terms of the spatial and temporal structure of the energy release. We also briefly discuss the observed quasi-periodic pulsations.
Morphology of average solar flares time profiles in microwave range
Authors: Motyk I. , Kashapova L.
Published: December 2024

Average flare time profiles are useful tools for determining energy evolution mechanisms both in the Sun and in stars. The study related to their construction and analysis was done in the visible and ultraviolet spectral ranges. Microwave emission, which is sensitive to various emission mechanisms, was not included in such studies. In this paper, we present the first results of reconstruction and analysis of average time profiles of solar flares using observations with the Siberian Radioheliograph. The events under consideration are flares with simple temporal behavior (without multiple bursts), but emitted in a wide frequency range. The latter feature was necessary to separate the emission of optically thick and optically thin sources. In total, we used 116 events detected during five months of observation in 2023 for the reconstruction. Each profile was normalized to its maximum value and the time scale was transformed into a universal length for all events, by deriving seconds into units equal to half the width of 50 % of the maximum value for each event ($t_{\frac{1}{2}}$). The time profiles of optically thin and optically thick emission sources demonstrate similar behaviour. The pulse phase fits well to a fourth-order polynomial function. The decay phase is fitted by two exponential functions. The emission dominance, fitted by one exponent over another, changes at $t_{\frac{1}{2}}$, which is approximately equal to 1.5.
The structure of the chromosphere along the northern limb of the Sun according to eclipse observations with RT-22 PRAO AKTs FIAN at a wavelength of 1.4 cm
Authors: Nagnibeda V. , Topchilo N. , Kovalenko A. , Rakhimov I.
Published: December 2024

An acute problem in the study of the solar chromosphere is the following obvious contradiction between the results of radio astronomical measurements of the height (extension) of the chromosphere and model calculations made on the basis of classical standard atmospheric models: the height of the chromosphere according to radio data is significantly greater than the model calculations. This is largely due to the fact that the widely used models are based on UV observations and, in addition, are one-dimensional and do not take into account the strong structural inhomogeneity of the chromosphere. Numerous attempts to ``improve'' the models by introducing various elements of inhomogeneity and ``fit'' them to radio data are purely empirical and are not substantiated theoretically. In such a situation, it is important to obtain more accurate and reliable radio observation data. This is all the more important because such data can serve as a basis for testing the recently developed 3D inhomogeneous theoretical models of the solar atmosphere. The article presents new data obtained from observations of a partial solar eclipse on June 10, 2021, using the RT-22 radio telescope of the Lebedev Physical Institute at a wavelength of 1.4 cm: the estimate of the radio radius is not more than 13''. The contradictions mentioned above remain significant.