Stellar-mass black hole binaries represent critical environments for exploring the complex coupling between relativistic gravity, angular momentum transport, and high-energy radiation. This work investigates how black hole spin and orbital separation modulate mass transfer efficiency, jet energetics, and emission behaviour in such systems. To this end, we employ a hybrid framework combining analytical models with two-dimensional general relativistic magnetohydrodynamics (GRMHD) simulations, focusing on variations in gravitational potential, inflow rate, and spectral structure across a range of black hole masses (M) and spin values (a). We introduce a novel empirical formulation for the mass transfer rate, M(r,M͙, a), which captures non-linear spin-radius coupling and enables accurate modelling of disk-jet interaction. Our simulations reveal that a critical spin threshold around a ≈ 0.7 leads to a steep rise in jet power, in alignment with Blandford–Znajek predictions. Furthermore, relativistically redshifted emission spectra derived from disk regions show strong agreement with observed X-ray data from Cygnus X-1 and V404 Cygni. These results establish a predictive link between system configuration and observable features, offering a robust foundation for interpreting spectral and timing behaviour in accreting black hole binaries.
Attempts to understand the mechanisms driving galaxy and their structures formation contributed to the formulation of various theoretical models describing this issue. Various scenarios make different predictions regarding the orientation of galaxies within large-scale structures, the distribution of their spins directions, and the alignment between the brightest galaxy in the cluster and the major axis of the structure. For this reason, the study of galaxy orientation provides a observational tool for testing models of their formation and remains a cornerstone of extragalactic astronomy and cosmology. The proper study requires consideration of the fact that galaxies are oblate spheroids with the real axis ratios dependent on the morphological type. However, most of the astronomical data available today lacks this type of information. As a result, a new method of investigation based on the estimated frequency of the occurrence of given morphological types of galaxies may prove to be an alternative. The method was applied to galaxies belonging to the clusters of the Local Supercluster using data from Sloan Digital Sky Survey. The obtained results confirm the theoretically predicted lack of significant alignment of the studied galaxies.
In this paper, we present a comprehensive analysis and validation of four exoplanet candidates, TOI-1001.01, TOI-1007.01, TOI-1019.01 and TOI-1032.01 selected from the NASA Exoplanet Archive. We use data from Transiting Exoplanet Survey Satellite (TESS) and apply the transit method to identify periodic dimming events, which are indicative of planetary transits. To obtain the best-fit and de-trended fluxes for our objects we used the the box-least squares (BLS) models. In addition, we performed odd-even transit and background-flux analysis for the further validation of candidates as true exoplanets.
In this work, we analyzed the orbits of over 35000 (as of 2024) near-Earth objects (NEOs) focusing on the potential for successive approaches to all pairs of planets: Earth, Venus, and Mars during the period from 2020 to 2120. We selected 120 candidates for fast transfers (within 180 days) between the following planet pairs: Earth-Mars, Earth-Venus, Mars-Earth, Mars-Venus, Venus-Earth, and Venus-Mars. We found only two candidates for double transfers (consecutive approaches involving three planets), and 10 candidates for multiple transfers, where an asteroid exhibits several consecutive paired approaches to planets within a century.
In this study, we present the detailed study of the geomagnetic storm that occurred 6-10 October 2015. In literature this storm was classified as a two-step storm due to the observation of two large decreases of the disturbance storm time (Dst) index during the main storm phase. In addition, the strong thermal emission velocity enhancement (STEVE) event occurred during the same storm phase was photographically documented by citizen scientists at Minnesota Nevis (USA). The storm of 7 October 2015, which exhibits high-intensity, long-duration, continuous AE activity (HILDCAA), is one of the strongest storms of the recent 24th solar cycle. We examined changes in Dst index, interplanetary magnetic field (IMF) Bz, flow velocity, proton density, solar wind pressure, epsilon parameters and presented the discussion of the physical mechanism happened during this geomagnetic storm. The results obtained for the storm on 7 October 2015 were also compared with geomagnetic storms occurred on 8 March 2008, 25 July 2016 and 8 September 2017.
In this paper we present the study of the photometric mass and density for the Tajikistan superbolide of 23 July 2008. Using the combined data from satellite and ground-based observations the mass was calculated by three approaches: photometric (based on the light intensity at the height of maximum brightness), graphics (using published data of cars) and using the kinetic energy of the superbolide. As a result, the calculated values of the mass are 25.3, 19.9 and 18.9 tons, respectively (with average value of 21.3 ± 2.1 tons). The superbolid density was evaluated using the drag equation, the equation density of atmosphere at the heights of the maximum luminosity and beginning of the train and criterion-PE. The densities calculated by these three methods are equal to 1.1, 0.53 and 0.95 g/cm3 (with the average superbolide density as 0.86 ± 0.15 g/cm3).
VarStar Detect is a Python package available on PyPI optimized for the detection of variability inside photometric measurements. Based off of the Least Squares method of regression, VarStar Detect calculates the amplitude of a Fourier Polynomial fit of the data as a measure of variability to assess if the star is indeed variable. This work shows the mathematical background of the package and an analysis of the code's functionality on TESS Sector 1 Data.
The paper presents the study of the dependence between photometric parameters of selected short-period comets of the Jupiter family and the activity of the Sun. As a quantity of solar activity, we used the sunspot area, the Wolf number, the annual mean solar radio flux, the solar flare index (full disk), and the annual mean AA-index solar activity. To study the correlation between cometary and solar activity the Dobrovolsky method was used. It has been found no direct correlation between the absolute stellar magnitude and the photometric parameter of comets with individual parameters of solar activity. Moreover, the correlation coefficients show that some comets are not associated with solar activity.
Using the data from Gaia (ESA) Data Release 2 we performed the orbital calculations of globular clusters (GCs) of the Milky Way. To explore possible close encounters (or collisions) between the GCs, using our own developed high-order φ-GRAPE code, we integrated backward and forward orbits of 119 objects with reliable positions and proper motions. In the calculations, we adopted a realistic axisymmetric Galactic potential (bulge + disk + halo). Using different impact conditions, we found four pairs of six GCs that may have experienced an encounter within twice the sum of the half-mass radii ('collisions') over the last 5 Gyr: Terzan 3 — NGC 6553, Terzan 3 — NGC 6218, Liller 1 — NGC 6522 and Djorg 2 — NGC 6553.
We analysed spectra of HD 126535 (K1 V), HD 127423 (G0 V) and HD 128356 (K2.5 IV) obtained with the spectrograph HARPS at the ESO La Silla 3.6 m telescope in Chile. Our synthetic spectral fitting procedure was firstly verified by analysing the spectra of the Solar and Arcturus, which were used as a template stars with well-known abundances. Comparison of obtained synthetic and observed spectra allowed us to identify 98 spectral lines of 10 chemical elements (Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni) within wavelength range 4500Å < λ < 7000Å. Abundances of each chemical element in the atmospheres of three studied stars were determined using the equivalent width of identified lines.
Galaxy clusters (GCs) are the largest and most massive gravitationally bound objects in the large-scale structure of the Universe. Due to keV temperatures of virialized gas in the intracluster medium (ICM) and presence of cosmic rays (CRs), GCs are effective sources of thermal X-ray radiation and non-thermal leptonic (synchrotron) radio emission. GCs are also store-rooms for hadronic CRs, but non-thermal hadronic gamma-ray emission (mainly, due to pp collisions and subsequent pion decay) from GCs has not been detected yet. In this work we simulate the expected non-thermal hadronic gamma-ray and neutrino emission from dominant part of Hercules cluster GC A2151 and estimate a perspective of detection of this emission by existing (Fermi-LAT, LHASSO, IceCube) and planned (CTA, IceCube-Gen2) ground-based ans space-based detectors.
In this research, five eclipsing binary stars were studied: AB Cas, AF Gem, AR Boo, BF Vir and CL Aur. The large sets of moments of minima were used: from the international BRNO database and amateur observations from the database AAVSO. Firstly, moments of minima for AAVSO observations were obtained (totally - 222 minima). The software MAVKA was used. It was kindly provided by Kateryna D. Andrych and Ivan L. Andronov (2019OEJV..197...65A) and approximation with various methods in order to find the best fit. Then all obtained moments of minima were combined and O-C diagrams were plotted. For all stars these diagrams represented sinusoidal-like oscillations with superposition of parabolic trend. One of the possible reasons for such oscillations could be presence of well-known light-time effect (LTE) caused by third component with elliptical orbit. Parabolic trend was explained as mass transfer between components of binary system. For all these stars we computed possible mass of the third component, orbital elements, mass transfer rate and errors for all computed values.
A careful and continuous ionospheric modelling can significantly influence the performance of activities such as Positioning, Navigation and Timing services related with the Global Navigation Satellite System applications as well as the Earth Observations System, satellite communication and Space weather forecasting applications. In this paper, the linear time-series modelling that consists of the solar, geomagnetic and periodic components has been carried out on the daily ionospheric vTEC at two different Ethiopian GPS locations, at Arbaminch, ARMI (geographic 6.06ºN, 37.56ºE) and Bahir Dar, BDMT (geographic 11.60ºN, 37.38ºE), for the year 2012, 2014 and 2016 in the 24th solar cycle. The variations of vTEC due to the solar activities, geomagnetic activities and periodic oscillations have been explicitly investigated. The results confirmed that the correlation coefficient of the linear model based estimated vTEC and the observed GPS-vTEC is around 80% in the year 2014. Besides, solar activity is identified as the key component for the 27 days period variations of vTEC whereas geomagnetic activity is identified as the key component that influences the short-period variations of the daily average vTEC. In addition to the correlation analysis, the accuracy of the model has been assessed by comparing the International Reference Ionosphere (IRI 2016) model based vTEC and GPS-vTEC measurements as well as with the quadratic model based vTEC. Consequently, the linear model formulated with the solar, geomagnetic and periodic components significantly captured the variations (78-80%) of the observed vTEC compared with both the IRI 2016 and the quadratic models during the years 2012, 2014 and 2016. The comparison of the observed and predicted vTEC variations has also been examined using the continuous wavelet transform. The decomposed waves from the wavelet analysis have revealed that the predicted and observed vTEC have had simultaneous periods of variations specifically with the period of 27 days whereas the IRI 2016 could capture the short-period variations of vTEC. Moreover, the analysis from the transformed data in the year 2014 over both Arbaminch and Bahir Dar has indicated that the linear model based vTEC and the observed GPS-vTEC have had common pattern of variations with the period of 27 days that had lasted for 150 days (from day of the year 100 to 250).
We present the new approach to the ionisation structure modelling for the high-metallicity H II regions. The method is based on the multicomponent photoionisation modelling (MPhM) of these objects that takes into account their complicate structure due to superwind from the central star-forming region. The complex structure of H II region has been divided into internal and external components. Internal components correspond to the region of free expanding superwind and the cavity of superwind, respectively, while the external ones — to a thick layer of gas compressed by a superwind shock, and hydrodynamically undisturbed outer part of H II region, where the most of observed strong emission lines are formed. The components of the model were calculated within the assumption of spherical symmetry. The gas photoinisation was caused by the ionising quanta of both direct and diffuse ionising radiation. The fluxes of this radiation were calculated during the simulation using the radiative transfer equations which account for all important processes in the H II region causing this transfer. The diffuse ionising radiation was calculated in the Outward Only approach. In the region of free expansion of the superwind the chemical abundances were determined using the evolutionary population synthesis models of a star-forming region. The distributions of the electron temperature and density in the external components were obtained in such modelling as the solutions of the photoionisation energy balance equation. The stop criterion for evolutionary modelling corresponding to the condition of equilibrium of pressure on the boundary between the third and fourth components was adopted. The evolutionary grid of multicomponent high-metallicity models of the H II regions was calculated. It was shown that the internal structure of a H II region under certain conditions can cause the lack of quanta in the spectrum of ionising radiation.
The HIFI instrument on board of the Herschel Space Observatory (HSO) has been very successful in detecting molecular lines from the circumstellar envelopes around evolved stars, like massive red supergiants, Asymptotic Giant Branch (AGB) and post-AGB stars, as well as the planetary nebulae. Among others, ammonia have been found in the circumstellar envelopes of C-rich AGB stars in amounts that significantly exceeded the theoretical predictions for C-rich stars. Few scenarios have been proposed to resolve this problem: formation of ammonia behind the shock front and photochemical processes in the inner part of the envelope partly transparent to UV background radiation due to the clumpy structure of the gas and formation of ammonia on dust grains. Careful analysis of observations may help to put the constraints on one or another mechanism of ammonia formation. Here, we present results of the non-LTE radiative transfer modeling of ammonia transitions including the crucial process of radiative pumping via the v2=1 vibrational band (at ∼10 μm) for V Cyg. Only the ground-based ammonia transition NH3 J = 10-00 at 572.5 GHz has been observed by HIFI. Therefore, to determine the abundance of ammonia we estimate the photodissociation radius of NH3 using chemical model of the envelope consistent with the dust grain properties concluded from the spectral energy distribution.
We report the results of observations of short time-scale variability in the Hydrogen Balmer lines and HeI lines in the hot B star ηUMa. Spectral observations were carried out with the low-resolution slitless spectrograph (R∼200) installed on the 60 cm Carl Zeiss telescope in the Andrushivka Observatory, Ukraine. Spectra were obtained with a time resolution in the sub-second range. It has been found that the hot B star ηUMa shows rapid variations in the Hydrogen lines Hβ, Hγ, Hδ, Hε and the Helium lines HeI 5016Å HeI 5047Å, as well as variations in the atmospheric oxygen lines. This can be interpreted that their variations are non-radial pulsations and strong stellar wind.
We present the results of spectral observations of comet C/2002 T7 (LINEAR) carried out at the 1-m Zeiss-1000 telescope of the Special Astrophysical Observatory (Russia). The spectra were obtained within the 3500-7500 Å wavelength range on November 13, 14, and 21, 2003, before the perihelion passage, when heliocentric and geocentric distances of the comet were about 2.7 AU and 1.8 AU, respectively. Spectra do not show any emission features from the strongest cometary emissions of the CN, C2, and C3 molecules. The normalised spectral gradient of reflectivity is 2.8% per 1000 Å and 5.4% per 1000 Å for November 14 and 21, respectively. The Afρ parameter, which characterises the dust production rate in the comet, is on average about 800 cm. Comet C/2002 T7 (LINEAR) can be classified as belonging to the group of dusty comets
In present work we analysed eight geomagnetic storm events in 2015/2016 and studied the possible influence of these events on Ethiopian power grids. The results showed that the majority of the forced power outages occurred in the period of the main phase of events and the recovery period of the geomagnetic storms. The geomagnetic storms are characterised by different indices and parameters such as the disturbance storm time (Dst) values, coronal mass ejection (CME) speed, solar wind speed (V sw) and interplanetary magnetic field (IMF-Bz) on the selected dates. In most cases the observed geomagnetic storms were produced by the CME-driven storms as they show a storm sudden commencement (SSCs) before the main storms, and also have the short recovery periods. The sudden jumps of the solar wind velocities and IMF-Bz are also consistent with occurrence of the CMEs. Moreover, this effect can be traced in changes of Earth magnetic field during geomagnetic storm and quiet days. The observed CME-driven storms can produce highly variable magnetic fields on the transformers and provide forced outages, however the studied outages have not been recognised as those one driven by a geomagnetic storm.
In this work we focused on observations of six trans-Neptunian objects (TNOs) whose apparent magnitudes are brighter than 20m. We present the results of astrometric and photometric observations of (134340) Pluto, (136108) Haumea, (136472) Makemake, (136199) Eris, (90482) Orcus, and (20000) Varuna obtained at the Kyiv comet station (Code MPC 585) in 2017-2019. For observations we used the 0.7-m (f/4) reflector AZT-8 with FLI PL4710 CCD camera and filters of Johnson-Cousins photometric system. From our images we measured the objects' astrometric positions, calculated apparent magnitudes in the BVRI (mostly R) bands using aperture photometry method, and found absolute magnitudes together with the colour indices in several bands. Analysing our results, we investigate the limitation on the astrometry and photometry of faint objects with the 0.7-m telescope.
The grid of new photoionisation models for planetary nebulae (PNe) along the evolutionary tracks of their nuclei was calculated, taking into account the dust presence with abundances that correspond to the averaged ones for Milky Way and Large Magellanic Cloud. The calculations were performed by the last version of G. Ferland's code Cloudy v17.01 using the semi-empirical law derived by Golovatyy-Mal'kov to describe the radial density distribution of matter in the nebular envelope of PN. Resulting modelling spectra were compared with the corresponding observed emission line spectra of PNe in optical range, obtained previously by other authors. Also the database of observations by the Infrared Space Observatory and Spitzer have been used to compare the results of synthetic photometry with the observed photometric data. It was shown that the intensities of strong emission lines in optical range as well as the observed color-color diagrams obtained using total fluxes in the 3.6 μm, 4.5μm, 8.0μm and 24.0 μm bands are reproduced very well by our models, while the results of synthetic IR-photometry based on total fluxes in the band 5.8 μm show discrepancies with corresponding observed data.
