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The chemical evolution of the Universe and several phases of the stellar life are regulated by minute nuclear reactions. The key point for each of these reactions is the value of cross sections at the energies at which they take place in stellar environments. Direct cross-section measurements are mainly hampered by the very low counting rate and by cosmic background, nevertheless they have become possible by combining the best experimental techniques with the cosmic silence of an underground laboratory. In the nineties the LUNA (Laboratory for Underground Nuclear Astrophysics) collaboration opened the era of underground nuclear astrophysics installing first a home-made 50 kV and later on, a second 400 kV accelerator under the Gran Sasso mountain in Italy: in 25 years of experimental activity, important reactions responsible for hydrogen burning could have been studied down to the relevant energies thanks to the high current proton and helium beams provided by the machines. The interest to the next and warmer stages of star evolution (i.e. post main sequence, helium and carbon burning) drove a new project based on an ion accelerator in the MV range called LUNA-MV, able to deliver proton, helium and carbon beams. The present contribution is aimed to discuss the state-of-the-art for some selected key processes of post main sequence stellar phases: the 12Cag and the 12C+12C fundamental for helium and carbon burning phases, and 13Can and 22Neag that are relevant to the synthesis of heavy elements in AGB stars. The perspectives opened by an underground MV-facility will be highlighted., 18 pages, 13 figures

Purpose: The overview of the scientifi c papers devoted to the study of the solar decameter radio emission with the world’s largest UTR-2 radio telescope (Ukraine) published for the last 50 years. Design/methodology/approach: The study and analysis of the scientifi c papers on both sporadic and quiet (thermal) radiation of the Sun recorded with the UTR-2 radio telescope at the decameter wavelength range. Findings: The most signifi cant observational and theoretical results of the solar radio emission studies obtained at the Institute of Radio Astronomy of the National Academy of Sciences of Ukraine for the last 50 years are given. Conclusions: For the fi rst time, at frequencies below 30 MHz, the Type II bursts, Type IV bursts, S-bursts, drift pairs and spikes have been recorded. The dependences of these bursts parameters on frequency within the frequency band of 9 to 30 MHz were obtained. The models of their generation and propagation were suggested. Moreover, for the fi rst time the fi ne time-frequency structures of the Type III bursts, Type II bursts, Type IV bursts, U- and J-bursts, S-bursts, and drift pairs have been observed due to the high sensitivity and high time-frequency resolutions of the UTR-2 radio telescope. The super-fi ne structure of Type II bursts with a “herringbone” structure was identifi ed, which has never been observed before. New types of bursts were discovered: “caterpillar” bursts, “dog-leg” bursts, Type III bursts with decay, Type III bursts with changing drift rate sign, Type III-like bursts, Jb- and Ub-bursts, etc. An interpretation of the unusually high drift rates and drift rates with alternating signs of the Type III-like bursts was suggested. Based on the dependence of spike durations on frequency, the coronal plasma temperature profi le at the heliocentric heights of 1.5–3RS was determined. Usage of the heliographic and interferometric methods gave the possibility to start studies of the spatial characteristics – sizes and locations of the bursts emission sources. Thus, it was shown that at the decameter band, the Type III burst durations were defi ned by the emission source linear sizes, whereas the spike durations were governed by the collision times in the source plasma. It was experimentally proved that the effective brightness temperatures of the sources of solar sporadic radio emission at the decameter band may reach values of 1014–1015 K. In addition, it was found that the radii of the quiet Sun at frequencies 20 and 25 MHz are close to the distances from the Sun at which the local plasma frequency is equal to the corresponding observed frequency of radio emission in the Baumbach–Allen model. Key words: UTR-2; Sun; decameter radio emission; radio bursts; corona

International audience; Purpose: A historical review of the experimental baselopment of low-frequency radio astronomy in Ukraine, its foundation half a century ago by an outstanding scientist S.Ya. Braude to the current state. Design/methodology/approach: The constant progress of electronic, computer and digital technologies, information and telecommunication technologies, theory and practice of antenna and receiving systems design, which introduction enriched the hardware and methodological ideology of construction and usage of the UTR-2, URAN, and GURT radio telescopes, have been used. Findings: The worldwide most effective national experimental radio astronomy means, the UTR-2, URAN, and GURT decameter-meter wave radiotelescopes, have been created and improved. The best combination of the systems main parameters: sensitivity; frequency band; spatial, frequency and temporal resolutions; noise immunity; uniformity of amplitude-frequency and space-frequency characteristics and multifunctionality has been provided. Conclusions: For the half a century of radio astronomical scientific and technical at the Institute of Radio Astronomy of NAS of Ukraine, the high astrophysical informativeness of the low-frequency radio astronomy and the possibility of creating a highly efficient experimental base – giant radio telescopes of decameter-meter wavebands have been proved. Today, the Ukrainian radio telescopes are well known and recognized world-wide being indispensable and most in demand by the scientific community. The founder of the decameter radio astronomy in Ukraine, the eminent scientist Semen Yakovych Braude was not mistaken when he decided to start radio astronomical explorations. The memory of him will always remain in the minds and hearts of many generations. Key words: low-frequency radio astronomy; radio telescope; phase shifter; antenna amplifier; digital signal recorder; effective area; sensitivity; resolution; noise immunity

Purpose: The studies of pulsars allow enriching our knowledge in determination of parameters of both the exotic electron-positron plasma in the pulsar magnetosphere with strong magnetic field and the ordinary ion-electron plasma of the interstellar medium, which exists in a weak magnetic field. To determine the parameters of the both plasma types it is reasonable to use polarization characteristics of a pulsed radio emission of pulsars. An accurate determination of these characteristics is quite a complex problem. For its solving, primarily we have to determine two parameters of the propagation medium – its dispersion and rotation measures. Their absolute values can be determined with the relative precision of 10-4, but the problem of rotation measure value sign determination arises. This sign depends on the interstellar magnetic field direction along the line of sight. Hear, a new method of rotation measure value sign determination is proposed. Design/methodology/approach: Muller polarization matrices are usually used for determination of such a propagation parameter as the rotation measure absolute value. When only one linear polarization is received, using of these matrices allows quite accurate determining the absolute value of the rotation measure, but not the sign of this parameter due to a certain symmetry of these matrices with respect to the direction of the linear polarization rotation plane. If we complement the system of equations, which determines the rotation measure value, with some new additional components, which take into account the contributions of the Earth ionosphere and magnetosphere to the rotation measure value, one can notice that this contribution is always positive in the Southern magnetic hemisphere (the majority of the Northern geographical hemisphere) and is always negative in the Northern magnetic hemisphere (the majority of the Southern geographical hemisphere). Moreover, the absolute value of this contribution is maximal at noon and minimal at midnight, when the concentration of ions in the Earth ionosphere is maximal and minimal, respectively. Accounting for these regularities allows to determine not only the absolute value of the rotation measure, but also its sign by means of two independent time-shifted estimations of the observed absolute value of this parameter for various ionization degrees of the Earth ionosphere. Findings: We show that using of additional equations, which take into account the contribution of the Earth ionosphere and magnetosphere to the value of the rotation measure parameter, allows full determination of this parameter accounting for the sign of this value even for the antennas, which can record a single linear polarization only. This approach allows to determine all polarization parameters of the pulsar radio emission as well as of the pulsed or continuum polarized radio emission of other cosmic sources. Conclusions: The paper presents the results of measurement of the rotation measure for the two closest to the Earth pulsars, namely J0814+7429 (B0809+74), J0953+0755 (B0950+08), and the comparison of the proposed technique for this parameter determination with other existing techniques. Key words: pulse, dispersion measure, rotation measure, plasma, polarization, pulsar, radio telescope

The generalization of the formula of a priori accuracy estimation for the case of implicitly given functions is performed. This is based on the classical definition of the root mean square error, which is given as the sum of the squares of the products of partial derivatives of the arguments and the errors of their definition. Differentiation of functions is carried out with the involvement of the theory of implicit functions of many variables, which does not require explicit assignment of the function by an analytical expression. The corresponding derivatives are determined by the differentiation of the equations in which the investigated function appears, according to the corresponding variables, including the function itself. Only the values of the function and arguments for which the accuracy is evaluated are required for the calculations. These values are found in different ways, including approximate methods for solving nonlinear equations (for example, Newton's method, half-division method). This approach is generalized to the case of several functions, which are already determined by a set of nonlinear equations. Their differentiation gives a linear system, which solutions are elements in the formulas for estimating the accuracy of each function. The solution of this system is determined by Cramer's method. Since the matrix of coefficients is the same for all linear systems, it is advisable to use the inverse matrix method to solve it. This significantly reduces the calculations. The values of the functions for which errors are determined are obtained from the set of equations that connect them. Finding them is much more problematic than for one variable. Thus, a strict priori estimate of accuracy is obtained without any restrictions on the studied functions, for example, in the form of their approximate representation by Taylor series or approximate estimates when solving equations. Proposed method is tested on test examples, which include the assessment of accuracy for both one and two variables, and is considered in the first case. The results of the calculations confirm the feasibility of using this technique. Therefore, with the traditional approach, the above algorithm can be used in more complex cases, i.e. for the case of implicit definition of the function.

There has been increasing necessity of more precise prediction and measurements of aviation radiation in Korea. For our air crew and passengers’ radiation safety, we develop our own radiation prediction model of KREAM. In this paper, we validate the KREAM model based on comparison with Liulin observations. During early three months of this year, we perform total 25 experiments to measure aviation radiation exposure using Liulin-6K in commercial flights. We found that KREAM’s result is very well consistent with Liulin observation in general. NAIRAS shows mostly higher results than Liulin observation, while CARI-6M shows generally lower results than the observations. The percent error of KREAM compared with Liulin observation is 10.95%. In contrast, the error for NAIRAS is 43.38% and 22.03% for CARI-6M. We found that the increase of the altitude might cause sudden increase in radiation exposure, especially for the polar route. As more comprehensive and complete analysis is required to validate KREAM’s reliability to use for the public service, we plan to expand these radiation measurements with Liulin and Tissue Equivalent Proportional Counter (TEPC) in the near future.

We develop the tissue-equivalent proportional counter (TEPC) type’s space radiation dosimeter to measure in-situ aviation radiation. That was originally developed as a payload of small satellite in the low-earth orbit. This dosimeter is based on a TEPC. It is made of an A-150 tissue-equivalent plastic shell of an internal diameter of 6 cm and a thickness of 0.3 cm. TEPC is filled with pure propane at 13.9 torrs to simulate a cell diameter of 2 μm. And the associated portable and low power electronics are also implemented. The verification experiments have been performed by the calibration experiments at ground level and compared with Liulin observation at aircraft altitude during the flight between Incheon airport (ICN) and John F. Kennedy airport (JFK). We found that the TEPC dosimeter can be used as a monitor for space radiation dosimeter at aviation altitude based on the verification with Liulin observation.

Purpose: The artificial satellites drag in the atmosphere remains an urgent problem to date. In this work, the artificial satellites data are used in order to study the atmosphere state under various manifestations of solar and geomagnetic activity. The selected satelites were moving uncontrollable being good indicators of the upper atmosphere state. The B-star (drag term) drag coefficient is used in this work. This term is used in the SGP and SDP models to take into account the resistance of the atmosphere to the satelite orbital motion. The data of the drag of two artificial satellites, one moving in elliptical and the other in circular orbits at midlatitudes (orbital plane angles of 58°-60°) were considered. These data include the end of the 23rd solar activity cycle, as well as the growth, the maximum and the decay phases of the 24th solar cycle (years 2005–2017). Seven periods of anomalous drag of the satellites were analyzed. They are: 4 monthly periods (two in 2005 and two in 2011) and 3 yearly periods (within 19.07.2014 to 22.08.2015), five-year long (2005–2010) and six-year long (2011–2017) periods. Design/methodology/approach: The periodogram analysis was made. This allowed to reveal the periodic processes in changes in the state of the atmosphere of different duration. The correlation coefficients of the B-star drag term with the indices of solar and geomagnetic activity were calculated. The analysis of extreme drag of the satellites in the periods of the increased solar and geomagnetic activity (intervals of observation lasting a month) was made. Findings: Using the solar and geomagnetic data we found that some month-long part of the anomalous drag periods were followed by flares on the Sun and the arrival of the coronal mass ejections into the near-Earth space. At time intervals of yearlong observations the highest values (0.5-0.7) were obtained for the coefficients of the B-star parameter correlation with the solar activity indices – solar radiation at the wavelength of 10.7 cm, F10.7, and Lyman alpha radiation, Lα. At monthly time intervals, the largest values of the correlation coefficients were obtained for the B-stars with the electron fluxes with energies above 0.6 and 2 MeV, E, (0.3-0.5), the Lyman alpha radiation, Lα, (0.58–0.73 for a сircular orbit satellite), and the solar constant, TSI, (0.3–0.6), as well as the geomagnetic storms intensity index, Dst , (0.66–0.69). Periodogram calculations show the presence of a whole spectrum of periods in the deceleration of a circular orbit satellite and a dedicated period for an elliptical orbit satellite. Conclusions: The B-star drag term dependences on the indices of solar and geomagnetic activity during some periods of their intensification for the 23–24 cycles of solar activity are considered. The periodogram analysis made together with the analysis of the conditions and parameters of space weather allows to see the general and more detailed picture of the solar and geomagnetic activity influence on the change in the motion of the satellite in the atmosphere. The B-star drag term helps to consider only the atmosphere influence on the artificial satellite movement in the near-Earth space. Key words: artificial satellite, atmosphere, artificial satellite drag, solar activity, geomagnetic activity, space weather

Purpose: Compilation of a digital catalog of magnetic storms in the Odesa magnetic anomaly zone in order to find the reasons for possible changes in the radiation fluxes of cosmic radio sources, according to observations at the URAN-4 radio telescope. Design/methodology/approach: Since 1987 until now, the radio flux of powerful galactic and extragalactic radio sources has been monitored at the URAN-4 radio telescope of the Odesa Observatory of the Institute of Radio Astronomy of the National Academy of Sciences of Ukraine. The monitoring program includes radio galaxies 3C274, 3C405 and supernova remnants 3C144, 3C461. Changes in the radio source flux level are determined by the ionosphere state due to the changes in space weather. At the “Odesa” geomagnetic observatory of the Institute of Geophysics of the National Academy of Sciences of Ukraine, the geomagnetic field measurements have been made since 1948. Simultaneously, the measurements of three elements of the geomagnetic field: horizontal component (H), vertical component (Z) and inclination (D), have been recorded. Findings: Using the “Odesa” geomagnetic observatory data, the digital catalog of magnetic storms was compiled for the measuring period of the powerful space radio source fluxes obtained with the URAN-4 radio telescope. For the magnetic storms monitored during the periods of 1987–1995 and 2000–2009, the date and time are shown for the beginning and the end of the magnetic storm, the magnetic storm duration, the amplitude of the three magnetic field elements, being H, Z, and D, and the magnetic storm type characteristic.The “Odesa” geomagnetic observatory is located near the magnetic anomaly zone. To find the distinctions in manifestations of the geomagnetic activity arisen owing to the magnetic anomaly existence, the geomagnetic disturbances recorded at the “Odesa” and “Moscow” (IZMIRAN, Russia) observatories were compared. It was shown that the total annual duration of the magnetic storms was longer in Odesa than in Moscow. This demonstrates some special role of the magnetic anomaly in the development of geomagnetic disturbances. Conclusions: The digital catalog of magnetic storms in the Odesa magnetic anomaly zone was compiled for the 1987–1995 and 2000–2009 periods. It is also planned to terminate working over the complete catalog of magnetic storms recorded at the “Odesa” observatory for the entire continuous period of monitoring space radio sources at the URAN-4 radio telescope in order to find the manifestations of geomagnetic disturbances impact upon the ionosphere state and changes of intensity in cosmic radio source fluxes. These studies are supplemented by the comparative analysis of the “Odesa” observatory geomagnetic data and the data from some other geomagnetic observatories. Key words: solar activity; monitoring variability of radio sources; magnetic storms; catalog of magnetic storms; magnetic anomaly

This paper presents an example of the application of theoretical developments on some issues of physics of space invasion. The effect of brightness oscillations and “wobbling” in the meteor trail, which we discovered, allows us to obtain estimates of some characteristics of the meteor by measuring the frequency of changes in the brightness in the trace (f_c) and meteoroid oscillations (f_m), if its velocity and altitude are known. Based on the proposed “tuning technique”, it is possible to determine the characteristics of the meteor at one-sided observations. To do this, we set the initial parameters for the model of meteoroid dynamics by the coincidence of the calculated and measured values of the frequencies f_c and f_m. Our simulation allows us to find the altitude at which the ratio of frequencies f_c/f_m coincides with the value found in the explosion of a meteoroid. Using this “tuning technique” and assuming the mineral composition for the meteor, we found estimates of the initial velocity of 21 km/s and the mass of 850 kg of the meteoroid, which reached a critical value of surface speed at an altitude of about 20.9 km in about 7.9 s with a residual mass of about 13.9 kg and a residual speed of about 10.9 km/s. At that moment, the meteoroid exploded.

Purpose: Based on the long-term study data in all radio spectrum ranges, the nature of deviations of spectral flux density of the Cas A supernova remnant from the tendency of its secular decrease is considered. The aim of this work is determining the presence of quasiperiodic variations and sporadic changes in the Cas A spectral radiation flux density depending on frequency. Design/methodology/approach: The main database is using the published results obtained with the method of absolute measurements of the Cas A spectral radiation flux density in a wide range from millimeter to decimeter wavelengths, as well as the results obtained with the method of relative measurements of the ratio of the flux densities of the Cas A supernova remnant and radio galaxy Cyg A, this latter being used as a reference source in the meter wavelength range. For making comparison with the aforesaid data obtained with different methods, the results of a long-term monitoring (since 1987) of the variation of the ratio of the spectral flux densities of Cas A and Cyg A made with the URAN-4 radio telescope of the Institute of Radio Astronomy of the National Academy of Sciences of Ukraine at 25 MHz were used. Findings: As a result of the analysis of the observed data for the Cas A radiation flux density in the entire radio wavelength range, the existence of quasiperiodic variations in the range from millimeter to meter wavelengths within 2 to 9 years has been noted. The reason for the detected quasiperiodic variations can be the processes in the Cas A remnant itself. In the decameter wavelength range, according to monitoring data obtained with the URAN-4 radio telescope, the seasonal-diurnal and long-term variations are noted, being associated with changes in the ionosphere state in the solar activity cycle, with some weak appearance of the secular decrease of the Cas A radiation flux. The presence of sporadic variations in the ratio of the spectral flux densities of Cas A and Cyg A is associated with the effect of the increased solar activity. For explaining the lowering of the Cas A spectral flux density to the Cyg A level and maintaining the excess of the Cas A flux at decameter waves, the quasi-simultaneous observations made with radiotelescopes for different wavelength ranges will be required. Conclusions: The evolution of the Cas A supernova remnant remains the focus of interest of current research efforts. An intriguing moment was the discovery of a point X-ray source in the center of radio source Cas A as a possible supernova remnant. The role of this source in the Cas A radio flux secular decrease and in its variations needs to be clarified. A detailed analysis of the long-term data and making quasi-simultaneous observations will allow to reveal the processes occurring in the radio source itself and to determine the influence of the ionosphere state on the results of measurements. A joint program is suggested for observations of Cas A and Cyg A flux variations with the RT-32 and RT-16 radio telescopes, the LOFAR element of the Ventspils International Radio Astronomy Center (Latvia), and the URAN, UTR-2 and GURT radio telescopes of the Institute of Radio Astronomy of the National Academy of Sciences of Ukraine. Key words: Cas A; secular radiation flux decrease; supernova remnant; ionosphere; solar activity Manuscript submitted 08.11.2020 Radio phys. radio astron. 2020, 25(4): 268 -275 REFERENCES 1. BAARS, J. W. M., GENZEL, R., PAULINY-TOTH, I. I. K. and WITZEL, A., 1977. 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A., KOUPRIANOV, V. V., LACLUYZE, A. P., MOFFETT, D. A., MOORE, J. P., STANLEY, J. L. and WHITE, S., 2017. The fading of Cassiopeia A, and improved models for the absolute spectrum of primary radio calibration sources. Mon. Not. R. Astr. Soc . vol. 469, is. 2, pp. 1299–1313. DOI: 10.1093/mnras/stx810 6. VINYAIKIN, E. N., 2007. Evolution of the radio spectrum of Cassiopeia A from long-term observations. Observations at 290 and 927 MHz. Astron. Rep . vol. 51, pp. 87–96. DOI:101134/S1063772907020023 7. VINYAIKIN, E. N., 2014. Frequency dependence of the evolution of the radio emission of the supernova remnant Cas A. Astron. Rep . vol. 58, pp. 626–639. DOI: 101134/S1063772914090078 8. MARTIROSSYAN, R. M., GOULYAN, A. G., SANAMYAN, V. A. and MANASELYAN, KH. A., 2020. Flux density variations of Cassiopea A radio source. Astrofizika . vol.45, no. 3, pp. 443–449. (in Russian). 9. HELMBOLT, J. F. and KASSIM, N. E., 2009. The Evolution of Cassiopeia A at Low Radio Frequencies. Astron. J . vol. 138, is. 3, pp. 838–844. DOI: 1088/0004-6256/138/3/838 10. WALCZOWSKI, L. T. and SMITH, K. L., 1985. A recurrence of the Cassiopeia A flux anomaly. Mon. Not. R. Astron. Soc . vol. 212, is. 1, pp. 27P–31P. DOI: 10.1093/mnras/212.1.27P 11. RYABOV, M. I., PANISHKO, S. K. and GUGLYA, L. I., 2011. Space weather impacts on the Earth’s upper atmosphere according to the monitoring of powerful radio sources fluxes at the URAN-4 radio telescope (Institute of Radio Astronomy, NAS of Ukraine). Odessa Astronomical Publications . vol. 24, pp. 159–161. (in Russian). 12. GORBYNOV, A. A., RYABOV, M. I. and PANISHKO, S. K. 2015. Secular Decrease the Flux of Supernova Eemnant Cas A on Monitoring Results to Radiotelescope “URAN-4” IRA NASU. Odessa astronomical publications . vol. 28, no. 2, pp. 224–226. 13. RYABOV, M. I. and SEROKUROVA, N. G., 1993. On the secular decrease of the radio flux Cas A at low frequencies. Astron. Astrophys. Trans . vol. 4, is. 1, pp. 29–32. DOI: 10.1080/10556799308205353

Purpose: Acoustic and atmospheric gravity waves (AAGW) are generated by many natural and anthropogenic sources. The AAGW propagation at ionospheric heights is accompanied by the generation of disturbances in the magnetic and electric fields. The plasma presence plays a crucial role. The mechanisms for generating electrical and magnetic disturbances in the near-Earth atmosphere by the AAGW have been studied much worse. Therefore, the validation of the capability to generate electromagnetic disturbances in the near-Earth atmosphere by the AAGW is an urgent problem. The purpose of this paper is to describe the mechanism for generating disturbances in the electric and magnetic fields in the near-Earth atmosphere under the action of AAGW and to estimate the amplitudes of these disturbances for various AAGW sources. Design/methodology/approach: The impact of a series of highenergy sources often results in the generation of synchronous disturbances in the acoustic and geoelectric (atmospheric) fields, when an approximate proportionality between the pressure amplitude and the amplitude of the disturbances in the atmospheric electric field is observed to occur. Based on the observational data and making use of the Maxwell equations, the theoretical estimates of the disturbances in the electric and magnetic fields have been obtained. Findings: Simplified expressions have been obtained for estimating the amplitudes of the electric and magnetic fields under the action of the AAGW generated by natural and manmade sources. The amplitudes of the electric and magnetic fields generated by the AAGW of natural and manmade origin, which travel in the near-Earth atmosphere, have been calculated. The amplitudes of the AAGW generated electric and magnetic fields are shown to be large enough to be detected with the existing electrometers and fluxmeter magnetometers. The magnitudes of the amplitudes of the electric and magnetic fields generated in the near-Earth atmosphere under the action of AAGW are large enough to trigger coupling between the subsystems in the Earth–atmosphere–ionosphere–magnetosphere system. Conclusions: The estimates and not numerous observations are in good agreement. Key words: acoustic and atmospheric gravity waves, near-Earth atmosphere, volume charge, atmospheric pressure disturbances, electric field, magnetic field

The ground tracking support is a critical factor for the navigation performance of spacecraft orbiting around the Moon. Because of the tracking limit of antennas, only a small number of facilities can support lunar missions. Therefore, case studies for various ground tracking support conditions are needed for lunar missions on the stage of preliminary mission analysis. This study analyzes the ground supporting condition effect on orbit determination (OD) of Korea Pathfinder Lunar Orbiter (KPLO) in the lunar orbit. For the assumption of ground support conditions, daily tracking frequency, cut-off angle for low elevation, tracking measurement accuracy, and tracking failure situations were considered. Two antennas of deep space network (DSN) and Korea Deep Space Antenna (KDSA) are utilized for various tracking conditions configuration. For the investigation of the daily tracking frequency effect, three cases (full support, DSN 4 pass/day and KDSA 4 pass/day, and DSN 2 pass/day and KDSA 2 pass/day) are prepared. For the elevation cut-off angle effect, two situations, which are 5 deg and 10 deg, are assumed. Three cases (0%, 30%, and 50% of degradation) were considered for the tracking measurement accuracy effect. Three cases such as no missing, 1-day KDSA missing, and 2-day KDSA missing are assumed for tracking failure effect. For OD, a sequential estimation algorithm was used, and for the OD performance evaluation, position uncertainty, position differences between true and estimated orbits, and orbit overlap precision according to various ground supporting conditions were investigated. Orbit prediction accuracy variations due to ground tracking conditions were also demonstrated. This study provides a guideline for selecting ground tracking support levels and preparing a backup plan for the KPLO lunar mission phase.

A CubeSat platform has become a popular choice due to inexpensive commercial off-the-shelf (COTS) components and low launch cost. However, it requires more power-efficient and higher-data rate downlink capability for space applications related to remote sensing. In addition, the platform is limited by the size, weight and power (SWaP) constraints as well as the regulatory issue of licensing the radio frequency (RF) spectrum. The requirements and limitations have put optical communications on promising alternatives to RF communications for a CubeSat platform, owing to the power efficiency and high data rate as well as the license free spectrum. In this study, we analyzed the performance of optical downlink communications compatible with CubeSat platforms in terms of data rate, bit error rate (BER) and outage probability. Mathematical models of BER and outage probability were derived based on not only the log-normal model of atmospheric turbulence but also a transmitter with a finite extinction ratio. Given the fixed slot width, the optimal guard time and modulation orders were chosen to achieve the target data rate. And the two performance metrics, BER and outage data rate, were analyzed and discussed with respect to beam divergence angle, scintillation index and zenith angle.

The study of meteoroids and the phenomena arising from their entry into the Earth's atmosphere is of considerable scientific and practical interest to obtain data on the origin and evolution of the solar system, to study the physics of planetary atmospheres, and to solve the problem of problem of asteroid-cometary-meteoroid hazard. Today the most effective and informative are photometric and spectral studies of meteor phenomena, which provide information on the chemical composition and physical properties (density, combustion temperature, etc.) of meteoroids that allow us to classify these bodies by parental origin and mineralogical structure. This paper presents the results of a study of the photometric system of eight meteor telescopes of the same type with a lens having a wide field of view (f = 50 mm, f / 1.2) and WAT-902H2 cameras. Telescopes equipped with broadband Cokin filters P050 (cyan) and P003 in the blue and red bands are installed in Mykolaiv and Odesa. An original method is used to observe meteors - the method of accumulation of shifted frames for TV cameras, which provide an accumulated image of reference stars in the form of points on a motionless telescope. In this work, simultaneous observations of reference stars in two filters obtained on 2 different observation nights were used. Cross-identification of the observational data with the Gaia DR2 catalog showed that the standard error of the residual coordinate differences (Obs – Gaia DR2) is about 7 "for both coordinates in both filters. The bandwidths of our filters are closest to the photometric system Gaia BP / RP, which was selected as a standard system to which the obtained instrumental stellar magnitudes were transformed. Transformation coefficients for converting instrumental stellar magnitudes into Gaia BP/RP photometric system were obtained by linear regression. Average standard photometric solution errors were 0.2 mag and 0.3 mag for red i and blue band, respectively. The possibility of determining the color index based on the array of common stars from observations in two bands is shown

The all-sky survey conducted by the InfraRed Astronomical Satellite (IRAS) in the 1980’s discovered many objects with infrared excesses whose nature has not been explored until recently. IRAS07080+0605 is one of those identified in the visual spectral range with an early-type star, which shows the B[e] phenomenon. The object is puzzling, because it exhibits one of the strongest infrared excesses associated with a star of one of the lowest surface temperatures (∼8500 K) among objects with the B[e] phenomenon, an apparent combination of spectral features of dwarfs and supergiants, and the absence of a surrounding optical nebula. Our photometric and spectroscopic study shows that the object’s properties are similar to those of the famous Red Rectangle proto-planetary nebula. In this paper we describe our findings and hypotheses about the nature and evolutionary status of IRAS07080+0605

Today, the study of stellar magnetic fi- elds is one of the important research field in astrophysi- cs because it provides us, in addition to physics, with information about space weather in the orbits of Earth- like planets in stars other than the Sun. Local magnetic fields on stars with convective envelopes are small-scale magnetic fields different in nature and structure from their global magnetic field. Unlike the Sun, through direct measurements we are able to measure only the magnetic field integrated over the visible disk of stars. However, we can register the magnetic field in the leading spot during the time interval when the corresponding magnetic flux tube already emerges on the surface of the star, and the magnetic flux tube of the following spot is still hidden in the interior under the photosphere. Our research is based on the spectropolarimetric observations carried out with 2.6m Shajn telescope equipped with the echelle spectrograph ESPL, CCD, and the Stokesmeter as a circular polari- zation analyzer. For measuring stellar magnetic fields the Single Line (SL) technique was developed at CrAO. This technique is based on the calculation of Zeeman effect in individual spectral lines. A key advantage of the SL technique is its ability to detect local magnetic fields on the surface of stars. Using SL technique emergence of large magnetic flux tubes at the surface of stars of V-IV-III luminosity classes (61 Cyg A, β Aql, β Gem) were first registered. We review the results of the study of local magnetic fields in these stars, includi- ng the results of modeling of magnetic field flux density and the size of their starspots. We also present the new results of spots modeling on β Aql. According to the considered geometric model, the rotational variabili- ty of the magnetic field and the extreme value of the field obtained from observations, we assume that the extreme radius of the spots at the surface of β Aql may exceed 9 ◦ .

The RR Lyr variable star Y Vul have been observed by using a CCD photometer during sev- eral seasons from 2011 to 2017. Nearly 5960 data points were obtained spanning over 53 nights. We found the amplitude and phase modulations with the amplitudes of 0.16 mag and 0.041 of the pulsating phase in V fil- ter; 0.15 mag and 0.041 of the pulsating phase in R filter, respectively. The frequency Fourier analysis of the light curves with the help of Period04 software was performed, Blazhko modulation period (59.20 days) and triplet structures in the Fourier spectrum were de- tected. The pulsation frequency components in the Fourier spectrum were identified up to the 7th har- monic order, while the modulation side lobe frequen- cies – up to 9th order. The analysis of the light curves maxima resulted in the same value of the Blazhko pe- riod.Thefundamental pulsation period of the star has been practically stable over a period of a hundredyears.

We present the results of a spectro- scopic and photometric investigation of 18 probable members of the open cluster Collinder 220, which contains the Cepheid UW Car. Besides the Cepheid, we studied tree K-giants, two B-giants, and twelve B-A-F main sequence stars. Radial velocities (RV), vsini, T eff , and logg were determined using spec- troscopic model fitting and atmosphere models. We have derived color-excesses, reddenings, and intrinsic colors for these stars using their T eff and logg from comparison to the atmosphere models, especially for hot stars. Proper motions, RV, and the GAIA DR2 2018 parallaxes allowed us to determine their membership in the cluster and absolute magnitudes. We found that seven stars along with the Cepheid can be the cluster members with a high confidence. The parallaxes and reddenings of the 7 confident cluster members led to the distances in a range of 1900–2800 pc, while the other stars are probably foreground objects. All the members have [Fe/H] near 0.1 dex. The B-giant HD90435 located near the cluster’s “turn-off” point has a low projected rotational veloc- ity, and this fact allows us to determine its chemical composition to compare with that of the Cepheid UW Car. The CNO abundances of HD90435 are nearly solar, while the Cepheid shows a deficit of carbon, an overabundance of nitrogen, a nearly solar oxygen, and an overabundance of sodium. The confident cluster member, K-supergiant CPD −57 ◦ 3199, has CNO- and Na abundances close to those of UW Car.

The research is devoted to the study of the life and work of the outstanding Ukrainian astronomer-the- oretician Kostyantyn Savchenko (1910–1956), who worked in the field of celestial mechanics and dynamic cos- mogony at the Kharkiv and Odesa astronomical observato- ries in 1930–1950 years. As a result of historio-graphic analysis, we found that till now there is no comprehensive study of his scientific biography besides several publica- tions related to certain facts of his life and activity, mostly in the Odesa period, including the reminiscences by Prof. V.K.Abalakin. Despite this, the vast majority of aspects of the scientist’s life, including his scientific and teaching ac- tivity in the Kharkiv period in 1930s, remains unexplored. The astronomer's scientific work was devoted to the study of the motion and rotation of celestial bodies with variable masses, the exploration of the perturbations of the planets by geometry methods, research of the physical nature of gravity, and the development of cosmogonic theories. We consistently describe the life and activity of Prof. K.N.Savchenko at the Kharkiv and Odesa astronomical observatories, the scientific and teaching work at the Kharkiv State University, the Kherson State Pedagogical Institute, and the Odesa State University, analyzing the archive documents and his scientific publications

Cosmic-ray induced γ-ray emission in active galactic nuclei (AGN) has been examined in this study for the first time. Cross-sections for the formation of γ-quanta in such cosmic-ray collisions were selected in the 1-150 MeV energy range. Synthetic γ-ray spectra were computed for both interstellar gas and dust. At the same energies of particle collisions and induced emission of γ- quanta, energy intervals of diagnostic interest were determined. Specific characteristics of emission were detected in the energy ranges of 5-15 MeV and 23-30 MeV for most investigated elements. Diffuse continuous γ-ray spectra for the other energy ranges were less informative with regard to the determination of the chemical composition of interstellar gas. It has been shown that exploring cosmic-ray fluxes in the vicinity of galactic centres by employing the examined γ-ray spectra yields a pattern of their energy distribution. Diagrams of cross- sections for γ-quanta formation were computed for the α- process elements. Synthetic γ-ray spectra of interstellar gas and dust were calculated individually and collectively. It has been indicated that, under certain conditions in AGN, cross-sections for ionisation of atoms due to energy losses by cosmic-ray induced ionisation and γ-quanta emission resulting from collisions with cosmic rays are similar. It has been found that when the maximum of proton and α- particle energy distribution function falls within the investigated range of energies, it leads to the formation of the peak flux of γ-rays. This is particularly important for the interpretation of observations in the energy ranges of 5- 15 MeV and 23-30 MeV. Synthetic induced γ-ray spectra of interstellar dust were computed, and methods of their observations for silicate and carbon-containing dust, which account for 80% and 20% of the interstellar-dust total mass, respectively, were determined. It has been deduced that the contribution of Compton processes to γ-quanta emission can be neglected at the investigated energies.

The photometry of space objects (SO) makes it possible to determine their state of rotation around the center of mass, orientation of the rotation axis and rotation speed in the most cost-effective manner. However, the methods for determining the attitude parameters from photometric data from a single observation site (OS) require long series of high-quality and high-frequency measurements. We propose a method for determining the orientation parameters of slowly rotating SO based on simultaneous multi-site photometry with a high temporal resolution. Preconditions for planning and building a local photometric network that can accomplish such a task have been tested via computer simulation. Synchronous observations of the unoperated spacecraft TOPEX/Poseidon were carried out. They were attended by the observatories of Odessa, Lvov and Uzhgorod universities, as well as the observation station of the State Space Agency of Ukraine in Zalistsi, Khmelnytsky region, took part. Synchronous network-based photometric observations from three OSs enable us to calculate time lags between correlated light- curve segments and promptly determine the direction of rotation, as well as the spatial orientation of a SO’s spin axis and its angular spin rate. A local network of several distributed observation sites for synchronous monitoring of the rotation of various SO in LEO will make it possible to determine the rotation parameters of also slowly rotating objects that do not exhibit glints within their light curves.

This paper presents the results of acomparative analysis of the relationship between solarcosmic rays (SCR), coronal mass ejections (CME), andcoronal shock waves (CSW) with the parameters of solarcontinual type IV radio bursts, as well as with the parame-ters of type II radio bursts. The sample under study con-tains 147 proton events accompanied by type IV continu-um radio bursts in the 25-15400 MHz range, type II radiobursts in the 25-180 MHz range, as well as CME and cor-onal shock waves. For the analysis, we used original rec-ords of solar radio emission at 8 fixed frequencies in therange 245-15400 MHz according to data from RSTN (Ra-dio Solar Telescope Network), original records of dynam-ic spectra from SRS (Solar Radio Spectrograph) in therange of 25-180 MHz, as well as original records intensityof the flux of SCR protons with proton energies in therange> 1-100 MeV according to data from the GOESspacecraft. A comparative analysis showed that the rela-tionship between the intensity of the SCR proton flux andthe CME velocity is, on average, much stronger with theparameters of type IV radio bursts than with the parame-ters of type II radio bursts, which indicates the dominantrole of the SCR acceleration process in the flare region,rather than shock waves. However, detailed studies of thefine structure of type II radio bursts have shown that thereis a fairly strong relationship between the intensity of theflux of mean-relativistic protons I p and the frequency f min,1at the fundamental harmonic (at the 1-st harmonic) at thetime t min corresponding to the minimum relative distanceb min between the harmonics of type II radio bursts. De-tailed studies of the fine structure of type II radio burstshave also shown that there is a strong relationship betweenthe intensity of the SCR proton flux I p and parameter V II ,which characterizes the displacement of the shock frontwith time t i in a narrow frequency range of 25-60 MHz, This paper presents the results of acomparative analysis of the relationship between solarcosmic rays (SCR), coronal mass ejections (CME), andcoronal shock waves (CSW) with the parameters of solarcontinual type IV radio bursts, as well as with the parame-ters of type II radio bursts. The sample under study con-tains 147 proton events accompanied by type IV continu-um radio bursts in the 25-15400 MHz range, type II radiobursts in the 25-180 MHz range, as well as CME and cor-onal shock waves. For the analysis, we used original rec-ords of solar radio emission at 8 fixed frequencies in therange 245-15400 MHz according to data from RSTN (Ra-dio Solar Telescope Network), original records of dynam-ic spectra from SRS (Solar Radio Spectrograph) in therange of 25-180 MHz, as well as original records intensityof the flux of SCR protons with proton energies in therange> 1-100 MeV according to data from the GOESspacecraft. A comparative analysis showed that the rela-tionship between the intensity of the SCR proton flux andthe CME velocity is, on average, much stronger with theparameters of type IV radio bursts than with the parame-ters of type II radio bursts, which indicates the dominantrole of the SCR acceleration process in the flare region,rather than shock waves. However, detailed studies of thefine structure of type II radio bursts have shown that thereis a fairly strong relationship between the intensity of theflux of mean-relativistic protons I p and the frequency f min,1at the fundamental harmonic (at the 1-st harmonic) at thetime t min corresponding to the minimum relative distanceb min between the harmonics of type II radio bursts. De-tailed studies of the fine structure of type II radio burstshave also shown that there is a strong relationship betweenthe intensity of the SCR proton flux I p and parameter V II ,which characterizes the displacement of the shock frontwith time t i in a narrow frequency range of 25-60 MHz.

We discuss the current state of problems associated with the discovery and study of exocomets, i.e objects of extrasolar systems, that are in many aspects similar to the solar system comets. Thus far, more than 4,300 exoplanetary systems have been discovered, but little is known about the populations of subplanetary bodies in these systems, in particular comets. Existing theories of planet formation suggest that populations of small bodies in the planetary systems should be numerous, especially at the early stages of their formation. Currently, most of the stars observed with the confirmed transit exoplanets and candidate stars with exoplanetary systems have been collected in the Kepler and TESS space mi- ssion databases. These databases can be used for a search and study of the exocomet transit signatures in extrasolar systems. So far, the number of observed cases of exocomet transits has been small, only about 20 events. Due to the rapid accumulation of data, new researches aimed to identify the specific transit events and study the physical characteristics of small bodies in the extrasolar systems are of great importance.Worth considering is the concept of “falling evaporating bodies”, massive enough bodies surrounded by mini- atmospheres, which fall on the parent star. The events might produce the variable, short-time red-shifts of some spectral features in their spectra. Alternative evidence of exocomet transits can be obtained by detection of the cometary emissions in CO, C, and O lines in the millimeter region of the spectra of debris disks by the ALMA and APEX telescopes. We discuss the known detection methods based on the analysis of the photometric and spectral series of observational data of space missions and ground- based complexes. Some results of experimental studi- es of the exocometary transit signatures obtained by other authors are presented and discussed.

In a recent paper, the model of thegalaxy with hot dark matter was considered. Thegalaxy is divided into the inner region with thedominant baryonic matter (the elliptic orbit of the testparticle) and the outer region with the dominant hotdark matter (the parabolic orbit of the test particle).It was assumed that the hot dark matter consists ofhypothetical Planck neutrinos arising in the decayof the protons at the Planck scale. Galaxies formedfrom the baryonic matter, and the hot dark matterappears in the galaxies later. The rotation curvesof the galaxies were studied in the model, includingMilky Way, M33, NGC 2366 and IC 2574. In thepresent paper, the hot dark matter model is furtherinvestigated, with the application to M31, the systemof M31 and the Milky Way, the globular clustersNGC 2419 and MGC1, the dwarf spheroidal galaxySculptor, ultra-massive quiescent galaxies from theCOSMOS and UDS fields. The baryonic matter massof M31 was estimated from the rotation curves, withthe average value 1.6 × 10 11 m ? . The gravitationalinteraction of the Milky Way and M31 is considered.In the hot dark matter model, the dynamical massesof the Milky Way and M31 are twice their baryonicmatter masses that gives the radial velocity of M31toward the Milky Way, 106 km s −1 . The hot darkmatter mass in the globular clusters NGC 2419 andMGC1 is estimated. The value is small comparedto the stellar mass in both the clusters. The hotdark matter mass within the half-light radius ofthe dwarf spheroidal galaxy Sculptor is estimated,0.5 × 10 6 m ? . The sum of the stellar and hot darkmatter mass within the half-light radius is consistentwith the dynamical mass within the half-light radiusof the Sculptor derived from the kinematics of themetal rich stars. The instability of the baryonicmatter due to the influence of the hot dark matterand some perturbations flattens the velocity profileof the metal poor stars which is unsuitable to derivethe dynamical mass. The evolution of ultra-massivequiescent galaxies from the COSMOS and UDS fieldsis considered. The dynamical to stellar mass relationis doubling during the evolution from z = 2 to 0 thatcan be explained by the absence of dark matter atz = 2 and the presence of the hot dark matter atz = 0., e outer region with the dominant hotdark matter (the parabolic orbit of the test particle).It was assumed that the hot dark matter consists ofhypothetical Planck neutrinos arising in the decayof the protons at the Planck scale. Galaxies formedfrom the baryonic matter, and the hot dark matterappears in the galaxies later. The rotation curvesof the galaxies were studied in the model, includingMilky Way, M33, NGC 2366 and IC 2574. In thepresent paper, the hot dark matter model is furtherinvestigated, with the application to M31, the systemof M31 and the Milky Way, the globular clustersNGC 2419 and MGC1, the dwarf spheroidal galaxySculptor, ultra-massive quiescent galaxies from theCOSMOS and UDS fields. The baryonic matter massof M31 was estimated from the rotation curves, withthe average value 1.6 × 10 11 m ? . The gravitationalinteraction of the Milky Way and M31 is considered.In the hot dark matter model, the dynamical massesof the Milky Way and M31 are twice their baryonicmatter masses that gives the radial velocity of M31toward the Milky Way, 106 km s −1 . The hot darkmatter mass in the globular clusters NGC 2419 andMGC1 is estimated. The value is small comparedto the stellar mass in both the clusters. The hotdark matter mass within the half-light radius ofthe dwarf spheroidal galaxy Sculptor is estimated,0.5 × 10 6 m ? . The sum of the stellar and hot darkmatter mass within the half-light radius is consistentwith the dynamical mass within the half-light radiusof the Sculptor derived from the kinematics of themetal rich stars. The instability of the baryonicmatter due to the influence of the hot dark matterand some perturbations flattens the velocity profileof the metal poor stars which is unsuitable to derivethe dynamical mass. The evolution of ultra-massivequiescent galaxies from the COSMOS and UDS fieldsis considered. The dynamical to stellar mass relationis doubling during the evolution from z = 2 to 0 thatcan be explained by the absence of dark matter atz = 2 and the presence of the hot dark matter atz = 0.

The network of the meteor observation in the radio range consisting of 6 stations located in Mykolaiv (3 stations), Rivne, Lviv and Hlukhiv has been created. The main goal of the network is to expand information about meteor phenomena, including the assessment of the kinematic parameters (velocities, radiants and orbital elements) of meteoroids and their relationship with other small bodies of the Solar system (potentially hazardous asteroids approaching the Earth). The operation of the meteor observing hardware and software complex is based on the continuous receving of signals from FM radio station reflected from ionized meteor trains that occur in the Earth's atmosphere at altitudes of 80-100 km. SDR technology is used to receive radio signals from over-the-horizon FM broadcast stations reflected by a meteor train, which has allowed to improve the sensitivity and frequency selectivity of radio signals. In 2017–2020 the network registered 1093015 meteors. The observational data are posted on the RMOB website. Diurnal variation of meteor counts and comparison with Perseids meteor stream activity are presented in the work.

The overview of the content of an Archive of the spectral photographic observational data stored at the MAO NAS of Ukraine in 1965–1985 is presented. Being the part of the UkrVO Joint Digitized Archive, this archive contains of 50,000 spectra of mostly variable stars. The spectral photographic material (glass astroplates) was obtained by the 70-cm reflector AZT-2 (MAO NAS of Ukraine, Kyiv), 60-cm Zeiss telescope at the Mount Ter- skol (North Caucasus, Russia), and 1-m telescope at the Mount Sanglok (Institute of Astrophysics, Tajikistan) equipped with spectrographs UAGS with a set of gratings to obtain dispersions in the range of 29…167 A/mm of the wavelengths 3500…6800 AA. There is also data related to the observations by the Double Short Astrograph (MAO NAS of Ukraine) with a pre-objective prism to monitor Nova Cygni 1975 in the initial stage of outburst. Almost all the spectra are calibrated with the 9-step attenuator and comparison spectra for the wavelength scale. We discuss observational programs (aims, instruments, results), in frame of which this archive was accumulated, as well as key principles for digitizing spectra and their pro- cessing by modern tools of virtual observatory software.

Observations of the comet were carried out using the OMT-800 telescope (the primary mirror diameter D = 80 cm; the focal length F = 214 cm) of the Odessa Observatory telescope network from January to June 2020. Image processing was per- formed through standard methods using subtraction of dark and flat field frames. The resulting frames were employed to analyse the morphology of the cometary inner coma using digital filters. Isophotes of the coma and images of its structures appearing as fans and jets were obtained. The presence of a strong fan, which distorts the coma’s standard appearance and makes it elongated perpendicularly to the Sun-comet line, is observed over the period from January to April. Later on, a weak jet that hardly affects the coma’s standard shape appears to replace the fan. The jet reaches its peak intensity near perihelion and then gets fainter rapidly. Such behaviour of the coma structures is indicative of the presence of two active areas on the cometary nucleus surface, for which the matter outflow is governed by the Sun illumination conditions. One of these areas, being more active, is responsible for the appearance of a strong fan. The other area, which is far less active, generates a jet that manifests itself near perihelion. The peak dust production of the comet 120–150 days before perihelion is due to the presence of an active fan in the inner coma.

We investigated the role of macroscopic turbulent diamagnetism in ensuring the long-term stability of the equilibrium state of the sunspots. The physical meaning of macroscopic diamagnetism of turbulent plasma is expulsion of a large-scale magnetic field from areas with increased turbulence intensity to areas with reduced turbulence. We follow the idea of Krause & Rüdiger (1975) that a strong magnetic field of a sunspot modifies the structure of turbulence in spot umbra, so it becomes two-dimensional. In addition, we take into account the strong magnetic suppression of turbulence in the spot, where it becomes less intense than the turbulent convection around the spot. As a result, a relatively thin transitional vertical layer of permeable convection (convective overshot layer) should be formed between these sections, in which the intensity of turbulent pulsations decreases noticeably in the transverse direction during the transition from the convection section to the spot. In this permeable convection layer, the effect of turbulent diamagnetic displacement of the magnetic field from the convection region to the sunspot occurs. Owing to the two-dimensional turbulent diffusion, the magnetic field of the spot spreads outwards, while the intense turbulent pulsations in the convection region return the magnetic field in the opposite direction, back to the spot. Therefore, these two oppositely directed processes of magnetic field transfer in the horizontal plane compete with each other. As a result, the magnetic fields that are transferred due to turbulent diffusion outward from the sunspot will be thrown backward into the spot due to strong external turbulent convection. In our opinion, this effect should ensure long-term stability of the equilibrium state of the magnetic field of sunspots and support them in the form of isolated vertical unipolar magnetic force tubes.

Low metallicity star HD121135 ([Fe/H] = -1.5) have been investigated spectroscopically. Its atmos- pheric parameters and elemental abundances have been determined, including elements of neutron (n-) capture processes, which are the keys in the study of early Galaxy enrichment. Na, Mg, Ni, Co, Sr, Y, Zr, Mo, Ba, La, Ce, Pr, Sm, Eu, Gd, Dy, Ho, Os, Th abundances were calculated using the synthetic spectrum method, factoring in the hy- perfine structure (HFS) for the Eu II lines. Si, Ca, Sc abun- dances were determined using the equivalent widths of their lines. The carbon content was computed by the molec- ular synthesis fitting for the region of CH (4300-4330 ÅÅ). For the abundances determinations of C, Na, Mg, Ba, and Th the NLTE corrections have been applied. We have determined for the first time the abundances of several n-capture elements and found that the behaviors of these elements do not show a significant trend with increasing atomic number. The elements ratios of [Eu/Fe] = 0.06, [Ba/Eu] = 0.13, [Sr/Ba] = - 0.05 do not support the HD121135 status as a r-process enrichment star. We have obtained the thorium abundance [Th/Fe] = 0.26. The car- bon content confirms the effect of canonical additional mixing in this star.

Thirty three spectra of the Polaris system obtained in August–December 2019 and February–April 2020 at the 0.81m telescope of the Three College Observatory (TCO, North Carolina, USA) were used to determine the radial velocities (RV) and effective temperature of the Cepheid Polaris Aa. These new data have been added to the entire Polaris system RV data collection (over 2,500 measurements) to compute a new orbit of the Polaris Aa companion. Furthermore we have used our eight observational datasets taken in 2015–2020 and eight datasets taken in 2011–2018 by Anderson (2019) to check for possible influence of the orbital motion of Polaris Ab on the Polaris Aa pulsational activity. It was found that the mean pulsational period in 2015–2020 was quite stable (3.976±0.012 days), while the pulsational amplitude showed evident changes: a growth before HJD 2457350 with a following decrease. This fact could be due to the Polaris Ab passing through the periastron.

Detailed description of the original pointing software used for spectral observations of the lunar exosphere is given. The software allows to point the spectrograph of 2-m telescope of Terskol Observatory inside and outside the lunar disk with accuracy of about 2″. Observations of Na lines in the exosphere of the Moon on January 8 and October 7, 2017, do not reveal quick variability of Na lines at time scales of about 20 minutes. On January 8, 2017, the intensity of Na lines above the south pole of the Moon was stronger than that above the north pole of the Moon.

Saturn's equatorial plane has an inclination of 26.75° to the plane of its orbit. Therefore, its atmosphere is characterized by seasonal changes. Because of the eccentricity of 0.056 orbit, the southern hemisphere receives 25% more energy from the sun than the northern one, because the aphelion of Saturn occurs in the summer in the northern hemisphere, and perihelion in the summer in the southern. At the moments of equinox, the planet is at an average distance to the Sun. We digitized up to 200 images of Saturn obtained by different observers at the equinoxes of 1966, 1980, 1995, 2010, and prepared brightness distributions along several latitudinal belts and along the central meridian in the spectral range of 300...890 nm. Using the available photometric and polarimetric data, we calculated the intensities of radiation diffusely reflected from the atmosphere within the framework of a two-layer model. In it, the upper layer is an optically thin gas layer, the lower one is a semi-infinite gas-aerosol layer. The atmospheric parameters were obtained by comparing the observational data with the calculated values. Analysis of the distributions of methane and ultraviolet (UV) absorption over the disk for the period 1964–2020. showed seasonal variations in the levels of formation of visible clouds and above-cloud fog. Meridional course of absorptions at equinoxes in 1966 and 1995 is the opposite of the course of changes obtained from observations at the 1980 equinox. But the expected difference in the course of absorption between the hemispheres of Saturn in 2010, and as that obtained in 1980, did not occur. Although all the orbital and physical characteristics on Saturn are repeated at the moments of the four equinoxes, the response of the atmosphere to them was different. The available seasonal models of Saturn's climate change are in good agreement with seasonal changes in methane and UV absorption in its atmosphere at the equinoxes of 1966, 1980, 1995. But the data from observations of the planet's hemispheres at the 2010 equinox showed a significantly different result. A study of observations from Voyagers and Cassini showed that at tropopause levels, the tropical regions of Saturn's atmosphere warmed by more than 10 K in one year (from 1980 to 2010). Such warming in the tropopause has significantly altered atmospheric stratification, stability, and influenced the large-scale dynamics of the upper troposphere. At the minimum of solar activity in 2010, atmospheric convection also significantly decreased.

Purpose: One-dimensional wire diffraction gratings, usually being mounted on ring frames, are often used in quasi-optical instruments under the construction of functional devices of different usage. Such gratings have been thoroughly studied theoretically and experimentally at the millimeter wavelengths, where they are most widely used and realized in various constructions of instruments and systems. However, a number of design and technological features of such gratings, connected with making the polarizing devices cannot be always taken into account in theoretical models that requires additional experiments. This problem is especially relevant in the terahertz range, where there is a lack of experimental data. This work aims at experimental studying the properties of one-dimensional wire gratings in the terahertz range at different angles of incidence of electromagnetic waves and for different adjustment conditions, as well as practical recommendations concerning the measurement technique and the creation of various polarizing devices. Design/Methodology/Approach: A measuring device has been developed and manufactured, in which a gas-discharge HCN laser (at the wavelength of 337 mm) is used as a radiation source. The study of one-dimensional wire gratings of two types was carried out: grating No. 1 (conductor diameter 70 μm, period 400 mm) and grating No. 2 (conductor diameter 50 μm, period 200 μm). The gratings were installed on a rotary stand. The stepper motor provided rotation within ±90°. Measurements were made automatically with a 0.35° step. The coefficient of laser radiation transmission through the grating was investigated depending on the angle of incidence and the adjustment accuracy. Findings: Analysis of the obtained data shows that the experimental results correlate with the theoretical data. Moreover, the experimental data more fully characterize the properties of the gratings, taking into account their design and technological features, which are very difficult to take into account theoretically. The resonance maxima in the experimental dependences of the transmitted power on the angle of incidence coincide with the calculated data that makes it possible to develop a number of new measuring techniques. Recommendations are given for improving the measurement accuracy and for the practical use of the obtained results. Conclusions: The obtained experimental results allow taking into account some additional features of the diffraction gratings, as well as improving the measurement technique. This is useful for the development of new devices in the terahertz range.

Purpose: The object of the radio study is to investigate dynamic processes, which occurred over the People’s Republic of China following three moderate (magnitudes 5.9-6.6) earthquakes in Japan in 2018–2019. The distances between the earthquake epicenters and the radio paths midpoints varied from approximately 1300 to 2000 km The aim of the study is to present observations of the dynamic processes in the ionosphere, which accompanied the earthquakes in Japan, and the analysis of intercomparison between the events. Design/methodology/approach: To continuously observe the ionosphere state over the ~ 100-300 -km altitude range, the multi-frequency multiple path radio system for oblique incidence soundings of the ionosphere has been designed by the specialists at the V. N. Karazin National University (Ukraine) and the Harbin Engineering University, PRC (45.78 N, 126.68 E). The basic premise upon which the system operation is based are the measurements of the Doppler shift of frequency, fD, and of the amplitude of radio waves reflected from the ionosphere. The Doppler spectra are calculated over the 20-s intervals, with the Doppler resolution of 0.02 Hz and the time resolution of 7.5 s. Findings: The seismic activity in Japan on July 7, 2018 was accompanied by an increase in a number of rays, by a significant broadening of the Doppler spectra, and by aperiodic processes in the ionosphere at distances no less than 1000–2000 km from the earthquake epicenters. Also, wave disturbances, generated by the seismic waves (speeds of ≈3 km/s), have been revealed in the 4–5-min infrasonic period range; the amplitude, δN, of the quasi-periodic variations in the electron density, N, was observed to be 4.5–9 %, and the duration of the oscillation trains to vary in the 24–55-min range. The relative amplitude δNa, of the electron concentration variations with the period ≈15-30 min caused by the propagation of atmospheric gravity wave (AGW) was estimated to be 30–55 %, the oscillation train duration was observed to be approximately 100 min, and the speed 0.3 km/s. The character of the Doppler spectrum variations, the Doppler shift of frequency over the main ray, and of the signal amplitude were found to be notably different during the September 5, 2018 earthquake and on the reference days. Two characteristic apparent speeds of 3.3 km/s and of ≈500 m/s were revealed. The former is close to that of seismic waves, and the latter to the speed of AGWs in the terrestrial ionosphere. The relative amplitudes in the infrasonic and AGW wave fields were estimated to be δN≈1.5-3 % and δNa≈6-7.5 %, respectively. The April 11, 2019 earthquake was accompanied by the Doppler spectrum broadening by 1-1.5 Hz in the 5–9.8 MHz frequency range, the generation of AGWs with 0.5-1 -km/s speeds and 8-20 -min periods, and by the generation of infrasonic waves with 2-5 -min periods and 0.3-0.4 -km/s speeds. Conclusions: Moderate earthquakes of Richter magnitudes ≈6 have been determined to give rise to dynamic processes in the ionosphere at distances no less than 1000-2000 km. The disturbances are transported by seismic waves with ≈3 km/s speeds and by acoustic and atmospheric gravity waves with 0.3–1 km/s speeds and periods varying from units to tens of minutes. Предмет і мета роботи: Предметом радіофізичного дослідження є динамічні процеси в іоносфері над Китаєм, що слідували за трьома помірними (магнітуда 5.9÷6.6) землетрусами в Японії в 2018–2019 рр. Відстань від епіцентру землетрусу до середини радіотраси змінювалася приблизно від 1300 до 2000 км. Метою роботи є викладення результатів спостереження динамічних процесів в іоносфері, що супроводжували землетруси в Японії, та їх порівняльний аналіз. Методи і методологія: Для безперервного спостереження за станом іоносфери на висотах ~ 100÷300 км використовувався багаточастотний багатотрасовий радіотехнічний комплекс похилого зондування іоносфери, розроблений фахівцями Харківського національного університету імені В. Н. Каразіна (Україна) та Харбінського інженерного університету (КНР, 45.78° пн. ш., 126.68° сх. д.). В основі функціонування комплексу лежать вимірювання значень доплерівського зміщення частоти fD й амплітуд відбитих від іоносфери радіохвиль. Доплерівські спектри обчислюються на інтервалі часу 20 с. Роздільна здатність за частотою становить 0.02 Гц, за часом – 7.5 с. Результати: Сейсмічна активність 7 липня 2018 р. в Японії супроводжувалася аперіодичними процесами в іоносфері на відстанях щонайменш 1÷2 тис. км від епіцентру, посиленням багатомодовості та значним розширенням доплерівських спектрів. Були також виявлені хвильові збурення в діапазоні інфразвукових коливань (період 4÷5 хв) генерованих сейсмічною хвилею (швидкість ≈ 3 км/с). Відносна амплітуда δN квазіперіодичних варіацій концентрації електронів N при цьому становила 4.5÷9 %. Тривалість цугу коливань була в межах 24÷ 55 хв. Відносна амплітуда δNa варіацій концентрації електронів з періодом ≈ 15÷30 хв, викликаних поширенням атмосферної гравітаційної хвилі, становила 30÷55 %. Тривалість хвильового цугу досягала приблизно 100 хв, швидкість – близько 0.3 км/с. Виявлено, що характер варіацій доплерівських спектрів, доплерівського зміщення частоти основної моди й амплітуди сигналу в день землетрусу 5 вересня 2018 р. та в контрольні дні помітно відрізнявся. Виявлено дві характерні удавані швидкості поширення збурень: 3.3 км/с і ≈500 м/с. Перша швидкість близька до швидкості сейсмічних хвиль, а друга – до швидкості атмосферної гравітаційної хвилі в іоносфері Землі. Відносна амплітуда в полі інфразвукової хвилі й атмосферної гравітаційної хвилі була δN ≈1.5÷3 % і δNa≈6÷7.5 % відповідно. Землетрус 11 квітня 2019 р. супроводжувався розширенням доплерівських спектрів на 1÷1.5 Гц в діапазоні частот 5÷9.8 МГц, генерацією атмосферної гравітаційної хвилі зі швидкістю 0.5÷1 км/с і періодом 8÷20 хв, і генерацією інфразвуку з періодом 2÷5 хв та зі швидкістю 0.3÷0.4 км/с. Висновки: Встановлено, що помірні землетруси з магнітудою ≈6 викликають динамічні процеси в іоносфері на відстанях щонайменш 1÷2 тис. км. Переносником збурень є сейсмічні хвилі зі швидкістю ≈3 км/с і акустико-гравітаційні хвилі з періодом від одиниць до десятків хвилин та зі швидкістю 0.3÷1 км/с.

This paper presents a methodology for Initial Orbit Determination (IOD) based on a modification of the Laplace’s geocentric method. The orbital elements for Near-Earth asteroids (1864) Daedalus, 2003 GW, 2019 JA8, a Hungaria-type asteroid (4690) Strasbourg, and the asteroids of the Main Belt (1738) Oosterhoff, (2717) Tellervo, (1568) Aisleen and (2235) Vittore were calculated. Input data observations from the Minor Planet Center MPC database and Astronomical Observatory of the Technological University of Pereira (OAUTP; MPC code W63) were used. These observations cover observation arcs of less than 22 days. The orbital errors, in terms of shape and orientation for the estimated orbits of the asteroids, were calculated. The shape error was less than 53 × 10–3 AU, except for the asteroid 2019 JA8. On the other hand, errors in orientation were less than 0.1 rad, except for (4690) Strasbourg. Additionally, we estimated ephemerides for all bodies for up to two months. When compared with actual ephemerides, the errors found allowed us to conclude that these bodies can be recovered in a field of vision of 95’ × 72’ (OAUTP field). This shows that Laplace’s method, though simple, may still be useful in the IOD study, especially for observatories that initiate programs of minor bodies observation.

Purpose: Analysis of the air temperature annual variations over different South American regions by long series of long-term meteorological observations, consideration of the physico-geographical and climatic features of the Amazonian lowlands, which affect thunderstorm activity in this region, search for the connection between seasonal variations in the Earth-ionosphere global resonator characteristics and air temperature in America, comparison of the results obtained in Antarctica with the surface temperature of American continent, checking the point source model validity for explaining the positions of the thunderstorm activity largest areas. Design/methodology/approach: The method of correlation analysis of time series was used. According to the long-term monitoring of the natural noise of the extremely low frequency range at the Ukrainian Antarctic Akademik Vernadsky Station, the seasonal changes in the Schumann resonance first mode level determined by the activity of the American thunderstorm center were retrieved. The average air temperature in the Amazonian lowlands was estimated for the same period according to the global network of meteorological stations Findings: The presence of a strong relationship between the surface air temperature of the equatorial and sub-equatorial regions of South America and the intensity of the Schumann resonance signal generated by the American thunderstorm center is shown. The hypothesis is confirmed that the Schumann resonator can play the role of a “global thermometer” and the model of an effective point source adequately describes the continental temperature changes. Conclusions: The developed technique is applicable for different points of Schumann resonance monitoring for studying all continental thunderstorm centers. This approach will be useful for developing the concept of using the Schumann resonator as a “global thermometer”. Using the data of simultaneous observations in several monitoring points can be considered promising for estimating short-term (days – several days) variations in global temperature.

In order to avoid the high cost and high risk of demonstration mission of rendezvous-docking technology, missions using nanosatellites have recently been increasing. However, there are few successful mission cases due to many limitations of nanosatellites like small size, power limitation, and limited performances of sensor, thruster, and controller. To improve the probability of rendezvous-docking mission success using nanosatellite, a rendezvous-docking phase analysis tool for nanosatellites is developed. The tool serves to analyze the relative position and attitude control of the chaser satellite at the docking phase. In this tool, the Model Predictive Controller (MPC) is implemented as a controller, and Extended Kalman Filter (EKF) is adopted as a filter for noise filtering. To verify the performance and effectiveness of the developed tool for nanosatellites, simulation study was conducted. Consequently, we confirmed that this tool can be used for the analysis of relative position and attitude control for nanosatellites in the rendezvous-docking phase.

Purpose: The purpose of the work is to develop a new method for determining the complex dielectric permeability of dielectrics in mm and submm wavelength ranges. Design/methodology/approach: The proposed method consists in registration of parameters of a plasmon polariton resonance, which arises at diffraction of electromagnetic radiation on a diffraction grating created on the surface of the conductive medium (metal or semiconductor) and registration of changes in these parameters when applied to the grating film of the material whose dielectric permeability should be found. On the laboratory unit, created on the basis of the terahertz HCN-laser, the dependence of the intensity of radiation, mirrored reflected from the grids, from the angle of incidence and determined the position and width of the plasmon-polaritone resonance for a clean grid and the same grid covered with the dielectric film. From comparison of these parameters, the values of the resonance shear and widening caused by the presence of the film were found. On the other hand, from the theoretical solution of the mentioned problem of diffraction under the conditions of a plasmon-polaritone resonance, the dependences of the resonance shear and width on optical characteristics of the investigated film (under the conditions of its small optical thickness) were found. Comparison of experimentally found and theoretically defined values of displacement and width of the resonance allows to determine the complex dielectric permeability of the film (at its known thickness). Findings: Test measurements of the complex dielectric permeability of the reference polypropylene film have been made by the proposed method. The measurements have been compared with the known data obtained earlier by spectroscopic and interferometric methods. It was found that the obtained and known values of the actual parts of the polypropylene dielectric permeability differ by less than 10 %, and the values of their imaginary parts coincide in the order of magnitude. Conclusions: The received results testify to suitability of the offered method for operational express measurements of optical characteristics of dielectrics films with small optical thickness.

Purpose: Due to the significant increase of a number of pulsars discovered with high-frequency radio telescopes over the last ten years and the necessity to obtain accurate parameters of their decameter radiation (as well as to identify single pulses detected with the UTR-2), the second decameter census of these sources with the UTR-2 radio telescope became needed. Design/methodology/approach: Single pulses detected as a result of the first decameter survey of pulsars and transient emission sources can be anomalously intense pulses of the recently discovered pulsars. Identification is only possible with an accurate information on the dispersion measure (DM) of each of these sources. Given that the new pulsars are likely to have a low radiant flux density, in contrast to the first decameter pulsar census [1], the second one plans to increase the signal-to-noiseratio by increasing the observation time of each pulsar. This paper gives a complete list of the studied sources, limited by the dispersion measure (DM< 30 pc·cm-³), period (P> 0.1 s) and declination (δ>-10º), known for the beginning of 2020, as well as some examples of the decameter pulsar radio emission detected by means of pipeline data processing with the possibility of flexible adjustment of search parameters. Findings: For the first time in the low-frequency wavelength range, the radio emission from the PSR J2325-0530, PSR J0613+3731, and PSR J1426+52 pulsars has been detected. The main result of present work is specified period for the latter pulsar (PSR J1426+52), being 0.995866 s ± 5 µs, the other parameters of its radio emission are also specified. Conclusions: High sensitivity of the UTR-2 radio telescope, its receiving equipment and efficient data processing and analysis pipeline allow detecting the decameter radiation of weak pulsars, as well as obtaining their parameters with the accuracy sufficient for identification of previously discovered transient signals.

This paper presents a kinematic ephemeris generator for Korea Pathfinder Lunar Orbiter (KPLO) and its performance test results. The kinematic ephemeris generator consists of a ground ephemeris compressor and an onboard ephemeris calculator. The ground ephemeris compressor has to compress desired orbit propagation data by using an interpolation method in a ground system. The onboard ephemeris calculator can generate spacecraft ephemeris and the Sun/Moon ephemeris in onboard computer of the KPLO. Among many interpolation methods, polynomial interpolation with uniform node, Chebyshev interpolation, Hermite interpolation are tested for their performances. As a result of the test, it is shown that all the methods have some cases that meet requirements but there are some performance differences. It is also confirmed that, the Chebyshev interpolation shows better performance than other methods for spacecraft ephemeris generation, and the polynomial interpolation with uniform nodes yields good performance for the Sun/Moon ephemeris generation. Based on these results, a Kinematic ephemeris generator is developed for the KPLO mission. Then, the developed ephemeris generator can find an approximating function using interpolation method considering the size and accuracy of the data to be transmitted.

Purpose: High resolution investigation of spectral lines of space sources requires low intrinsic noise of the radio telescope receiving system. It is provided with both input cryogenic amplifiers and low phase noise of local oscillators. To make spectral studies, it is neces ary to be able to tune the frequencies of local oscillators with a small frequency step. The paper presents the results of developing the frequency synthesizers, which simultaneously provide both a very high frequency resolution and low level of phase noise. The results of measurements of natural noise of the RT-32 radio telescope radio receiving systems are given also. Design/methodology/approach: The RT-32 receiving systems are constructed as heterodyne receivers with two stages of frequency conversion. Tuning of receiving systems with a frequency step of 10 or 20 MHz is provided by local oscillators of the first frequency conversion stage, and precise tuning is provided due to the ultra-high resolution (0.0001 MHz) of DDS-based (direct digital synthesizer) local oscillators of the second frequency conversion stage. Findings: It is shown that the application of direct digital synthesizers is possible only with the low values of frequency multiplication factors, as well as under the conditions of careful filtering of all reference signals. The parameters of the local oscillators were measured with the N9951A spectrum analyzer (Keysight Technologies) with the high resolution and wide dynamic range. To measure the radio telescope receiving system noise characteristics, a special matched loads with the possibility of cooling down to the liquid nitrogen temperature were made. The noise temperature measurements were made in different cross sections of the RT-32 receiving system. Comparison of such measurements in different configurations makes it possible to provide a preliminary estimation of the RT-32 self noise in the C- and K-bands. Conclusions: The results of measurements of self noise of radio receiving systems and phase noise of local oscillators of the RT-32 radio telescope show that within the C-band the radio telescope is capable to perform high-sensitive studies in both a wide frequency band and a narrow frequency band with the high spectral resolution. Within the K-band, the natural noise is comparable (≈60÷80 K) with the external noise that also allows studying the radiation of maser radio sources. Key words: antenna, self noise, local oscillator, receiving system, radio telescope, RT-32, spectral lines Manuscript submitted 15.07.2020 Radio phys. radio astron. 2020, 25(3): 1 75-192 REFERENCES 1. ULYANOV, O. M., REZNICHENKO, O. M., ZAKHARENKO, V. V., ANTYUFEYEV, A. V., KOROLEV, A. M., PATOKA, O. M., PRISIAZHNII, V. I., POICHALO, A. V., VOITYUK, V. 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This paper describes the initial operations and preliminary results of the Instrument for the study of Stable/Storm-time Space (ISSS) onboard the microsatellite Next Generation Small Satellite-1 (NEXTSat-1), which was launched on December 4, 2018 into a sun-synchronous orbit at an altitude of 575 km with an orbital inclination angle of 97.7°. The spacecraft and the instruments have been working normally, and the results from the observations are in agreement with those from other satellites. Nevertheless, improvement in both the spacecraft/instrument operation and the analysis is suggested to produce more fruitful scientific results from the satellite operations. It is expected that the ISSS observations will become the main mission of the NEXTSat-1 at the end of 2020, when the technological experiments and astronomical observations terminate after two years of operation.

Muons and neutrons are representative secondary particles that are generated by interactions between primary cosmic ray particles (mostly protons) and the nuclei of atmospheric gas compounds. Previous studies reported that muons experience seasonal variations because of the meteorological effects of temperature. The intensity of neutrons has a typical modulation with various periods and reasons, such as diurnal and solar variation or transient events. This paper reports that cosmic ray particles, which were observed by neutron monitors, have seasonal variations using the daily data at the Oulu neutron monitor. To eliminate the effects of solar activity across time, the daily data were normalized by two different transformations: transformations with respect to the grand mean and yearly mean. The data after transformation with respect to the yearly mean showed more statistical stability and clear seasonal variations. On the other hand, it is difficult to determine if the seasonal variation results from terrestrial effects, such as meteorological factors, or extraterrestrial effects, such as the position of the Earth in its orbit of revolution.

This paper reports on the optical imaging polarimetry of geostationary satellite Express-AM5.Precise optical polarimetry was carried out using the Nayuta 2-m telescope at Nishi-Harima Astronomical Observatory and a polarimeter. V-band images were continuously taken in 312 minutes. The degree of polarization decreased with time until the minimum phase angle was reached at midnight, and then, it increased until morning. This change in the degree of polarization is well explained by the reflection of sunlight from monocrystalline solar panels of the satellite and possibly from other satellite components such as the antenna dishes and/or bus., This paper reports on the opticalimaging polarimetry of geostationary satellite Express-AM5. Precise optical polarimetry was carried out usingthe Nayuta 2-m telescope at Nishi-Harima Astronom-ical Observatory and a polarimeter. V -band imageswere continuously taken in 312 minutes. The degreeof polarization decreased with time until the minimumphase angle was reached at midnight, and then, it in-creased until morning. This change in the degree ofpolarization is well explained by the reflection of sun-light from monocrystalline solar panels of the satelliteand possibly from other satellite components such asthe antenna dishes and/or bus

Purpose: An experimental study of signatures of traveling ionospheric disturbances (TID) observed in diurnal-seasonal variations of the parameters of probe HF signals propagating on theoblique single-hop RWM–LFO radio path, derived from the yearlong monitoring data. Design/methodology/approach: A long term digital recording of the HF radio signals’ waveforms of the Exact time and frequency service station (RWM, Moscow, Russia) was made at the Low Frequency Observatory of the IRA NAS–Ukraine (LFO, Martove, Kharkіv reg., Ukraine). The Doppler frequency shift (DFS) was derived from the power spectra of the recorded signals. The DFS quasiperiodic variations were interpreted as the result of passage of traveling ionospheric disturbances associated with the acoustic-gravity waves (AGW) at the height of the F-layer of ionosphere. The value of the DFS variation period was determined as the sum of the time intervals between neighboring zero crossing of two consecutive half-periods, and the amplitude was determined as the range of variations. The cases of F region shielding by the underlying ionospheric layers Es and E were taken into account as well. Findings: The data on the periods and amplitudes of the DFS variations were used for statistical analysis. The probability of DFS variations’ observation was determined for each month. This value lies within 81 to 91 % in winter and spring and decreases to within 52 to 80 % in summer and autumn seasons. It is shown that the rise of electron density in the lower layers of the ionosphere Es and E makes it difficult to detect TIDs in the F region. This results in a significant underestimation of the probability of observation in the summer and partially in the spring-autumn seasons. The diurnal-seasonal dependences of the probability of DFS observation, as well as their periods and amplitudes were determined. The forms of daily distributions of both amplitude and period are generally similar for all the seasons. They show two peaks, one in the morning and the second one in the evening, and the minimum in the afternoon. As respects the seasonal distributions of periods and amplitudes, in summer, a higher median value of period and more even distribution of amplitude are observed. In addition, we evaluated the influence of the level of geomagnetic storminess on the characteristics of DFS variations. It was determined that a rise of geomagnetic activity (K-index ≥2) is accompanied by decreasing of the observation probability and increasing of the amplitudes and periods of DFS variations. Conclusions: The techniques developed for the analysis of the data of Doppler ionospheric sounding by non-special type HF signals can be used for diagnostics and analysis of the ionospheric disturbances.

Purpose: Detection of wave processes of various temporal and spatial scales in the mid-latitude ionosphere over the Eastern Europe near the characteristic geophysical time periods (equinoxes and solstices) during magnetically quiet and weakly disturbed conditions at low solar activity; estimation and calculation of traveling ionospheric disturbances (TIDs) characteristics based on the analysis of variations in the incoherent scatter radar signal power corresponding to electron density disturbances; analysis of TIDs generation sources. Design/methodology/approach: The time dependences of the incoherent scattering signal power were processed, and further bandpass filtering of data in various ranges of periods dominant modes was made. To remove slow signal variations (trend) and fast oscillations which may be caused by noise, the initial time series were passed through a digital filter with the wide bandwidth of 5–125 min. The spectral analysis was further made to localize the predominant oscillations on the time and period axes. Further, this range was divided into three subranges: 15–30, 30–60 and 60–120 min. For each of these subranges, the dominant TIDs were determined and their characteristics were estimated. Vertical components of phase velocity and disturbance wavelength were determined by the cross-correlation analysis, and their horizontal components were evaluated using the dispersion equation for acoustic-gravity waves (AGWs). Findings: Large and medium-scale TIDs were identified at altitudes from 100 to 400 km. The spectral analysis showed that for all the seasons the predominant quasi-periodic disturbances with periods within 60 to 120 min had the highest energy. The TIDs with periods within 15 to 120 min lasted from 2 to 10 h. We identified 59 TIDs in total. Most of them (49 events) were most likely associated with the AGW propagating upward (their sources were located at lower heights). The average values of large-scale perturbations in the subranges of 30-60 min (the average oscillation period being 45 min) and of 60-120 min (82 min): the maximum relative amplitude of variations – 0.14 and 0.20, respectively; the vertical phase velocity – 105 and 56 m/s; the horizontal phase velocity – 495 and 473 m/s; the vertical wavelength – 285 and 282 km; the horizontal wavelength – 1358 and 2322 km. The average values of these parameters for the medium-scale AGWs/TIDs in the subranges of 15–30 min (the average period being 22 min) and of 30–60 min (41 min) were respectively 0.13 and 0.13; 127 and 64 m/s; 289 and 268 m/s; 166 and 157 km; 403 and 658 km. It has been demonstrated that the largest number of TIDs is observed near the winter solstices and autumn equinoxes. Conclusions: As a result of a long-term systematic monitoring of the ionosphere state with the Kharkiv incoherent scatter radar, the characteristics of TIDs being observed in the periods close to equinoxes and solstices at low levels of solar and geomagnetic activities have been determined. The presence of largescale TIDs even under magnetically quiet conditions is proved. The plausible sources of the detected TIDs are discussed. The results obtained will improve the knowledge of the mid-latitude TIDs characteristics, as well as contribute to improvement of the global and regional models of the ionosphere.

Purpose: The effect of the Earth’s ionosphere and interplanetary plasma on the radio astronomy observations, in particular, interferometric ones, at decameter waves has been investigated. The amplitude and phase fluctuations of an incident electromagnetic wave field are observed upon diffraction by a plasma layer with inhomogeneities of electron density. In interferometric observations, the phase fluctuations of an output signal cause a decrease in coherence time and an increase in the interferometer response spectrum width that limits the time of coherent averaging and reduces the instrument sensitivity. The purpose of the study is to assess the degree of ionospheric and interplanetary scintillations influence on the sensitivity of interferometric observations and to determine the possibility of sensitivity increasing that is needed in observations of angular structure of weak compact radio sources. Design/methodology/approach: To determine the contribution of ionospheric scintillations to the broadening of an interferometer output signal spectrum, the radio source with such an angular size, which prevents its scintillations on the solar wind inhomogeneities, but makes it possible to observe the source using the URAN-2 interferometer with the baseline of 153 km, was used. Processing a large amount of observational data made it possible to determine the signal spectrum width at the output of thе interferometer under the condition of amplitude and phase scintillations on ionospheric inhomogeneities. Then, the interferometer was used to observe a compact radio source, whose signal fluctuations are affected by both the ionosphere and the interplanetary medium. The preliminary obtained spectral widths of the ionosphere scintillations made it possible to single out the effect of just interplanetary inhomogeneities on the interferometer response. Findings: The constraints on the time of coherent averaging imposed by the influence of interplanetary plasma have been determined. Some suggestions as for changing the method of observation with the URAN interferometers at decameter wavelengths are made for more correct and efficient study of weak compact objects. The influence of large-scale features of the solar wind structure, related to the form of lines of force of the interplanetary magnetic field and to the form of spatial spectrum of inhomogeneities on the sensitivity of low-frequency interferometric observations was found. An increase in turbulence of the interplanetary medium beyond the Earth’s orbit lasting up to several days, conjugate with manifestations of the sporadic solar activity, was also detected. Conclusions: The study allows to determine the interplanetary medium influence on the limitation of sensitivity in the interferometric observations and find optimal elongations for studying the angular structure of weak radio sources. An account of solar activity events can be used for a short-term forecast when determining the strategy of highly sensitive observations. The proposed method for detecting the solar wind turbulence can be used in studying the process of interaction of the solar events with the interplanetary medium.

Purpose: The problem of an H-polarized plane wave diffraction by the infinite double-layer non-ideally periodic strip grating is considered. The grating is obtained from the ideally-periodic one by excluding of a single strip in each layer. The purpose of this paper is to build the rigorous mathematical model based on the operator method, the study of the fields scattered by the structure. Design/methodology/approach: The field scattered by the grating is found as a sum of three summands. The first one is the field scattered by the ideally periodic grating. The second one is the field of currents on the two strips being absent in the structure under consideration (with the minus sign). The third one is the correction field caused by the absence of the strips. The operator equations with respect to the Fourier amplitudes are obtained for every field. In these equations, the scattering operators of a single layer are used. A short-form algorithm of their determination based on the method of singular integral equations is represented. Findings: The obtained numerical results allow to make a conclusion about the behavior of the field scattered by the grating. The numerical study of convergence is made. The stop bands and pass bands can appear at the double-layer gratings. In the case of strips being absent in each layer, the waveguide channel can be formed; the incident wave can transmit through this channel even when the parameters correspond to the stop band. The dependences of the reflection and transmission coefficients on the frequency, which allow to determine the position of the stop bands and pass bands are given. The diffraction patterns of the transmitted field and near field distribution are built. Conclusions: An effective algorithm for studying the field scattered by the double-layer infinite grating in the absence of strips in each layer is suggested. The obtained results indicate a significant dependence of the width of the transmitted field main lobe vs. frequency. The developed approach can be effective in solving of a number of antenna technique and microwave electronics problems.

Properties of plasmas that constitute the plasma sheet in the near-Earth magnetotail vary according to the solar wind conditions and location in the tail. In this case study, we present multi-spacecraft observations by Cluster that show a transition of plasma sheet from cold, dense to hot, tenuous state. The transition was associated with the passage of a spatial boundary that separates the plasma sheet into two regions with cold, dense and hot, tenuous plasmas. Ion phase space distributions show that the cold, dense ions have a Kappa distribution while the hot, tenuous ions have a Maxwellian distribution, implying that they have different origins or are produced by different thermalization processes. The transition boundary separated the plasma sheet in the dawn-dusk direction, and slowly moved toward the dawn flank. The hot, tenuous plasmas filled the central region while the cold, dense plasmas filled the outer region. The hot, tenuous plasmas were moving toward the Earth, pushing the cold, dense plasmas toward the flank. Different types of dynamical processes can be generated in each region, which can affect the development of geomagnetic activities.