Showing papers in "Kinematics and Physics of Celestial Bodies in 2020"

Ionospheric Effects of the August 11, 2018, Solar Eclipse over the People’s Republic of China

Abstract: The purpose of the work is to describe ionospheric effects of the August 11, 2018, partial solar eclipse (SE) that occurred over the People’s Republic of China as observed via GPS technology. Solar eclipses are rare phenomena of nature. During 2–3 h, the rearrangement of processes acting at the Earth’s surface, in the atmosphere, geospace, i.e., in the Earth–atmosphere–ionosphere–magnetosphere system (EAIMS), occurs. The response of this system depends on the solar activity, season, time of day, and on the state of atmospheric and space weather. Therefore, the investigation of the EAIMS response to SEs remains an urgent problem. The response is accompanied by controllable dynamic processes, the study of which improves our understanding of the near-Earth environment. Studying the EAIMS response to SEs is of fundamental importance to science. Its practical applications include the following. Solar eclipses cause significant disturbances in EAIMS, which affect the propagation of radio waves in almost all frequency ranges and, as a result, deteriorate the performance of radars, radio astronomy and radio navigation systems, and tools for remote environment sensing. SE effects have been studied for over 100 years. Thus far, the following regular effects have been studied quite well: reductions in the electron density, electron and ion temperatures, variations in ion composition, and plasma vertical movements. The irregular effects have been studied to a much less extent, and they can vary from one solar eclipse to another. The main feature of the SE over the PRC has been the fact that it was observed during the time before local time sunset period. The maximum magnitude of the eclipse within the PRC area varied from 0.07 to 0.52, while the Sun’s surface area shadowed by the Moon was observed to be 0.02–0.42. The onset of the eclipse over the PRC has been observed to occur in the period ∼09:54–10:05 UT, and the ending time varied from 10:07 UT to 11:10 UT. The SE duration varied from a few minutes to approximately 67 min. The insignificant duration of the eclipse and the dusk terminator affected the SE effects. The state of space weather during the solar eclipse was favorable for observing SE effects occurring in the ionosphere. The global navigation satellite system data have been processed to reveal the ionospheric response to the August 11, 2018, SE. The ionospheric time delay and, respectively, the vertical total electron content (TEC), have been calculated combining the pseudo-range and integrated-phase data at two frequencies. Regardless of the dusk terminator influence, we have managed to confidently detect the ionospheric SE effects, which proved to be sufficiently small due to a small SE phase. Over the People’s Republic of China area, a funnel-shaped decrease in TEC has been observed to occur approximately 1300 km in latitude and 2000 km in longitude. The TEC reduction has been found to be 7%. The solar eclipse was accompanied by the generation of aperiodic TEC disturbances at a rate of 0.4–0.8 TEC unit/h and 105-min in duration. Wave disturbances caused by the SE have not been observed confidently, which is due to a small SE phase and insignificant disturbances in the electron density.

Geomagnetic Variations Caused by the Lipetsk Meteoroid's Passage and Explosion: Measurement Results

Abstract: The magnetic effect of meteors was first observed and theoretically explained back in the middle of the 20th century. The mechanisms for the magnetic effect of large celestial bodies (1–10 m and more) fundamentally differ from the mechanisms of geomagnetic field disturbances caused by meteors at ionospheric heights. The passage of a large meteoroid through the atmosphere and its explosion are accompanied by the generation of a powerful shock wave and the formation of a plume, which result in a geomagnetic effect. To the present day, researchers are divided on the main mechanism for the geomagnetic effect of large meteoroids. The Tunguska and Chelyabinsk meteoroid measurements are available for studies. In the case of the Chelyabinsk meteoroid, the variations in the geomagnetic field are detected and explained both prior to and after the explosion of this celestial body. Analyzing observations of the passage of any large enough celestial body is of considerable theoretical and practical interest. The purposes of this study are to present the analysis of magnetic field variations that arose as a result of the Lipetsk meteoroid passage through the Earth’s magnetosphere and atmosphere and to estimate and discuss the magnetic effect and its mechanisms. The fall rate of such meteoroids is 0.68 yr–1. Using the data provided by the Magnetic Observatory of Karazin Kharkiv National University (Kharkiv, Ukraine), the temporal variations in the horizontal components of the geomagnetic field on June 21, 2018, (the day of the Lipetsk meteoroid passage) and on June 20 and 22, 2018, (the reference days) have been analyzed. The meteoroid’s initial speed was 14.4 km/s, the initial mass was 113 t, and the initial size equaled approximately 4 m. The distance from the observatories to the site where the meteoroid explosion-like release of energy occurred was 360 km. The passage of the Lipetsk meteoroid in the magnetosphere and atmosphere has been shown to be accompanied by alternating variations in the geomagnetic field components. The magnetic effect of the magnetosphere was observed 54–56 min before the meteoroid explosion; the amplitude of the disturbance in the geomagnetic field did not exceed 0.5–1 nT, and the duration was 15–20 min. Alternating spikes (first positive, then negative) in the H and D component level were observed after the meteoroid explosion with a ∼6-min delay. The spike amplitude was ∼1.2–1.5 nT, while the duration of the magnetic effect from the ionosphere reached tens of minutes. The models for the magnetic effects observed are suggested and theoretical estimates are performed. The observations and the estimates are in good agreement.

Asymmetry of Lines in the Spectra of the Sun and Solar-Type Stars

Abstract: The asymmetry of the Fe I and Fe II lines in the solar flux spectra has been analyzed using three FTS atlases and the HARPS atlas; it was also analyzed in the spectra of 13 stars using observations on the HARPS spectrograph. Individual line bisectors of each star have been averaged to reduce observation noise. The obtained average bisectors in the stellar spectra are more or less similar to the C-shape well known for the Sun. In stars with rotation velocities greater than 5 km/s, the shape of the bisectors is closer to the slash symbol (/). The curvature and span of the bisectors increase with the temperature of the star. Our results confirm the known facts about the strong influence of rotation velocity on the span and shape of bisectors. The average convective velocity was determined based on the span of the average bisector, which shows the largest difference between the velocity of cold falling and hot rising convective flows of matter. It is equal to –420 m/s for the Sun as a star. In solar-type stars, it grows from –150 to –700 m/s with an effective temperature of 4800 to 6200 K, respectively. For the stars with greater surface gravity and greater metallicity, the average convective velocity decreases. It also decreases with star age and correlates with the velocity of micro- and macroturbulent movements. The results of the solar flux analysis showed that absolute wavelength scales in the FTS atlases coincide to approximately –10 m/s, except for the atlas of Hinkle et al., the scale of which is shifted and depends on the wavelength. In the range from 450 to 650 nm, the scale shift of this atlas varies from –100 to –330 m/s, respectively, and it equals –240 m/s on average. The resulting average star bisectors contain information about the fields of convective velocities and may be useful for hydrodynamic modeling of stellar atmospheres in order to study the characteristic features of surface convection.

The second reprocessing campaigns of historical observations in the GNSS data analysis centre of MAO NAS OF Ukraine

Abstract: The second reprocessing campaign of historical observations of GNSS satellites at permanent stations located in Ukraine and in the Eastern Europe for GPS weeks 935–1708 (December 7, 1997 – October 6, 2012) was carried out in the GNSS Data Analysis Centre of the Main Astronomical Observatory NAS of Ukraine with using products updated in IGS repro2 and EPN-Repro2 campaigns – precise ephemerides of GPS and GLONASS satellites, coordinates and velocities of reference permanent GNSS stations, etc. The observations was analyzed with the Bernese GNSS Software ver. 5.2 according to the requirements of the EUREF Permanent GNSS Network (EPN), that were valid at that time. In total, observations on 72 GNSS stations, including 48 Ukrainian stations belonging to the following operators of GNSS networks: MAO NAS of Ukraine, Research Institute of Geodesy and Cartography, TNT TPI company (TNT TPI GNSS Network), PJSC System Solutions (System.NET), Lviv Polytechnic National University, UNAVCO, Inc. (USA), were processed. The IGb08 reference frame was realized by applying No-Net-Translation conditions on the coordinates of the IGS Reference Frame stations. As result, the stations’ coordinates in the IGb08 reference frame and the zenith tropospheric delays for all stations were estimated. The mean repeatabilities for components of stations’ coordinates for all weeks (the characteristics of the precision of the received daily and weekly solutions) are in the following ranges: for north and east components – from 0.6 mm to 1.6 mm (average values are 1.02 mm and 0.94 mm respectively), for height component – from 2.2 mm to 5.2 mm (average value is 3.36 mm) with the outlier of 5.79 mm for GPS week 943. The coordinates of the permanent GNSS stations for one weekly solution are presented.

Development of Firehose Instability of a Magnetosonic Type in the Presence of High-Speed Proton Beams

Abstract: One of the varieties of firehose instability, whose cause is not the temperature anisotropy of plasma particles but the dynamic pressure of the beam, is considered. It is shown that such a generation mechanism can lead to an effective increase in low-frequency perturbations not only of the Alfven type but also of the magnetosonic type and also lead to instability not only in the finite and high-pressure plasma but also in a low-pressure plasma. The characteristics of magnetosonic waves that are generated during the development of instability are investigated. The growth rate, the maximum inclination angle of the wave vector, the propagation velocity of the perturbations, and the criterion for the development of instability are found. The influence of the beam temperature on the characteristics of the generated perturbations is studied. As an example of the development of such instability, the formation process of the turbulent region in front of the shock wave of the Earth, as well as before the shock wave from the supernova, is analyzed.

Parameters of the Infrasonic Signal Generated by the Kamchatka Meteoroid

Abstract: The subject of this study is the infrasonic signal generated by a high-speed (32 km/s), high-energy (173 kt TNT), and large-sized (9.4 m) celestial body, later called the Kamchatka meteoroid, which entered the terrestrial atmosphere and exploded on December 18, 2018. The focus of the study is the parameters of the infrasonic signal launched by the Kamchatka meteoroid. The study is based on the data on temporal dependences of pressure in the infrasonic wave collected by the I53US, I30JP, I59US, I46RU, I57US, and MAAG2 infrasonic stations included in the International Monitoring System (IMS) set up by the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO). The measurement data initially recorded on a relative scale were converted into absolute values. The temporal dependences of the infrasonic wave pressure were then filtered in the 1–40-s period range and were subsequently subjected to system spectral analysis that included the mutually complementary short-time Fourier transform, adaptive Fourier transform, and the wavelet transform with the Morlet wavelet as the basis function. As a result, it was found that the infrasonic signal amplitude exhibits quite a rapid decrease with distance between an infrasonic station and the meteoroid’s explosion site. The time delay of the infrasonic signal shows an increase with distance between the celestial body explosion and the site of signal detection. The signal celerity exhibits a dependence on the distance and the path orientation; it is estimated to be in the range of 269–308 m/s. The infrasonic signal duration shows virtually no dependence on the distance from the detonation point to an infrasonic station. The infrasonic signal spectra have a wide bandwidth with periods from ∼5 to ∼40 s. At the same time, the greatest energy falls within the isolated periods of 12–15 s and 28–33 s. The scatter diagrams and regressions for the infrasound main parameters were plotted. The celestial body’s kinetic energy (179 kt TNT) and acoustic efficiency (∼4%) were estimated from the prevailing infrasonic period.

Two-Frequency Propagation Mode of Acoustic−Gravity Waves in the Earth’s Atmosphere

Abstract: As is known from multiyear theoretical and experimental studies, acoustic−gravity waves (AGW) determine the dynamics and energy balance of the atmospheres of planets and the Sun to a considerable extent. Linear wave perturbations in the atmosphere can be described with a system of second-order equations for the vertical and horizontal components of the perturbed velocity. It follows from this system that small perturbations in the atmosphere may be considered as oscillations of coupled oscillators with two degrees of freedom. This suggests that it is worth studying more thoroughly the linear acoustic−gravitational wave modes in the atmosphere with well-developed methods of the theory of oscillations. To study small perturbations in the Earth’s atmosphere, the methods of the theory of coupled oscillatory systems were used. It has been shown that acoustic−gravity waves in an isothermal atmosphere can be considered as a superposition of oscillations that occur simultaneously at two natural frequencies—acoustic and gravitational. The equations for the natural frequencies of oscillations, as well as for the components of the perturbed velocity under specified initial conditions, were derived. From the analysis of temporal changes in the components of the perturbed velocity, new features in their behavior were found. All solutions are presented with the use of real quantities only. This representation is more convenient for comparison with observational data than the complex one commonly used in the theory of acoustic−gravity waves. The conditions under which the usual single-frequency oscillation mode can be realized in the atmosphere are analyzed. The results of the study can be used to explain some features in space-borne observations of wave perturbations in the Earth’s atmosphere that do not fit the framework of the known theoretical concepts.

Generation of the Sun’s Radial Magnetic Field by Global Hydrodynamic Flows

Abstract: A theory on the emergence of global hydrodynamic flows of matter and the generation of global magnetic fields in the solar convective zone is proposed. The unstable profile of differential rotation plays a crucial role in it: all hydrodynamic flows on the Sun (poloidal circulation, torsion oscillations, and spatiotemporal variations of the poloidal flow) are generated due to the loss of stability of differential rotation. None of the models known to us, wherein torsion oscillations and variations of the meridional circulation are typically calculated separately and are thus considered to be independent flows, reproduce this result. The calculations within our model suggest, on the contrary, that the indicated flows are actually toroidal and poloidal components of a single, 3-dimensional global flow. The decisive role of torsion oscillations in the generation of the radial alternating magnetic field is highlighted in the present study. It is demonstrated by numerical simulation that the time-varying radial magnetic field on the surface of the Sun reaches its maximum at the poles, where it changes polarity with a period of ~22 years. This process may be identified with the observed effect of polarity reversal of the polar field within the Hale magnetic cycle. It is demonstrated that the lines of zero values (polarity reversal) of the surface radial magnetic field pass through the maxima of the velocity modulus of zonal flows (torsion oscillations). In addition, the lines of magnetic polarity reversal of the radial field and the maximum velocities of surface zonal flows drift from the poles to the equator. It is noted that the obtained results on the latitudinal evolution of surface zonal flows correlate with the behavior of deep zonal flows determined by processing helioseismological data.

Morphology of the flare-productive active region NOAA 9087

Abstract: Evolution and morphological properties of the active region NOAA 9087 are analyzed based on space and ground observational data Data on hard X-ray (HXR) and soft X-ray (SXR) were obtained from Yohkoh Telescopes (HXT and SXT) and the Geostationary Operational Environmental Satellite Magnetograms and images in far ultraviolet were obtained from the Michelson Doppler Imager (MDI) and Extreme ultraviolet Imaging Telescope (EIT) of the Solar and Heliospheric Observatory (SOHO) White light images from the Big Bear Observatory (BBSO) and Hα-filtergrams from the Meudon Observatory were used Data on the 269 GHz radio flux were taken from the World Data Center of the Learmonth Observatory (Australia) The investigated active region (AR) was observed on the solar disk from July 15 to 27, 2000, and showed a complex multipolar magnetic field configuration A high flare activity and emissions were observed in this AR According to Solar Geophysical Data (SGD), the 3N/M64 two-ribbon flare occurred on July 19, 2000, and lasted 25 h The energy was released sequentially in different locations in the AR All observational data indicate a continuous change in the structure and power of the flare at different wavelengths HXR and type III radio bursts were observed at the initial phase of the flare The HXR coronal source was above the line of magnetic polarity inversion of the AR Observational evidence of magnetic reconnections during the main phase of the flare is obtained based on the analysis of sequential images of loops in the ultraviolet wavelength band Postflare loops were observed in the 195 nm passband at the gradual phase, which is a manifestation of the EUV late phase These extended loops connect the primary and secondary energy release sites of the flare There was an additional energy transfer and heating mechanism during the main phase of the flare

Accumulation of Fourier Component Phases during Observation of an Object with an Orbital Telescope

Abstract: In the case of astronomical observations from the surface of the Earth, it is difficult to obtain high resolution images due to the distorting influence of the atmosphere. There are two groups of methods for mitigating this influence. The first group does not interfere with the process of image formation and is related to the processing of already recorded images. The methods from the second group involve constructing special observational instruments. Placing the instrument outside the atmosphere may also be considered a method from this group. In this case, there is no atmospheric influence, and acquisition of images with diffraction-limited resolution is assumed to be possible without additional effort. The factors that may lead to phase distortions during observations with an orbital multimirror telescope are discussed. The total phase accumulation method is proposed for removing the distortions. The method is designed for compensating for the distortion of Fourier component phases caused by the Earth’s atmosphere. Assumptions as to the statistics of phase distortions used in its development are quite general and do not interfere with its application to space observations. Computer modeling is used to demonstrate the technique effectiveness and study its capabilities in processing images from a multimirror space telescope. The use of modeling as an instrument for research is motivated by the high cost and complexity of the real experiment and the necessity of having a true image of an object for evaluating the method error. The aperture configuration of the upcoming James Webb Telescope is used for modeling. The modeling was used to explain the different behavior of phase distortions between space observations and observations from the Earth’s surface. It is demonstrated that, in case of space observations, the total phase accumulation is required instead of the main phase values' accumulation. It is found that the dependence of the reconstruction error on the number of accumulated images is nonmonotonic.

Characteristics of Infrasonic Signals Generated by the Lipetsk Meteoroid: Statistical Analysis

Abstract: The purpose of this paper is to construct basic correlation diagrams and plot the respective regression functions for the parameters of the infrasonic signals launched by the Lipetsk meteoroid. The celestial body that entered the Earth’s atmosphere at 01:16:20 UT on June 21, 2018, had the following initial parameters: 14.4 km/s speed, approximately 113 t mass, approximately 4 m size, and approximately 2.8 kt TNT kinetic energy. The infrasonic signals generated by the celestial body were observed on a global scale, and they were recorded by the International Monitoring System (IMS) set up by the Comprehensive Nuclear-Test-Ban Treaty Organization’s International Monitoring System (CTBTO). For data processing, techniques of mathematical statistics have been invoked. The basic results of the study are as follows. The infrasonic signal exhibits a linear dependence of the infrasonic signal time delay on the horizontal distance from the meteoroid explosion epicenter, and the signal celerity averaged over all propagation paths is estimated to be approximately 304–305 m/s. The infrasonic signal celerity first shows a rapid enough decrease with distance, but over the 4.5–8.66-Mm distance range exhibits fluctuations at approximately 302 m/s. The duration of the infrasonic signal shows a linear decrease with distance, and the signal duration dispersion is insignificant in the 5–8 Mm distance range. The mean periods of the infrasonic signal, independent of distance and averaged over various regression functions, are estimated to be 6.28 ± 0.98 s and 6.14 ± 0.76 s. The mean of the initial kinetic energy estimated using the oscillation period of the infrasonic signal is 2.26–2.43 kt TNT, which differs insignificantly from the NASA estimates (2.8 kt TNT). The approximation for the dependence of celerity versus sine of the back-azimuth angle of arrival shows that the corrected value of the celerity is approximately 300 m/s, and the mean of the troposphere-stratosphere wind is approximately 25–31 m/s. Analysis of the correlation diagrams has shown that a steady statistical link exists between the true and observed back-azimuth angles of infrasound sources. It is noted that the level of fluctuations in the azimuth tends to increase with distance.

The Distribution Function of Cosmic Rays at the Initial Stage of a Solar Proton Event

Abstract: The propagation of solar cosmic rays in the interplanetary medium is considered on the basis of the kinetic equation describing the small-angle multiple scattering of charged particles Energetic particles are assumed to be injected into the interplanetary medium by an instantaneous point-like source The spatial-temporal distribution of the density and anisotropy of high-velocity particles during the anisotropic phase of a burst of solar cosmic rays is studied An analytical expression for the distribution function of cosmic rays in the small-angle approximation is derived; the evolution of the angular distribution of energetic particles is investigated It has been shown that, under weak scattering of charged energetic particles on fluctuations of the interplanetary magnetic field, the intensity of solar cosmic rays impulsively increases at the initial stage of their enhancement The anisotropy in the angular distribution of solar cosmic rays monotonously decreases with time and exhibits the highest value at the moment of the first particles' arrival to a given point of space

Influence of Vertical Heterogeneity of Atmospheric Temperature on the Propagation of Acoustic-Gravity Waves

Abstract: A new approach to the study of acoustic-gravity waves in the Earth’s atmosphere in the presence of vertical temperature inhomogeneity is proposed. Using this approach, the local AGW dispersion equation was obtained for the atmosphere with a small vertical temperature gradient. The modification of the acoustic and gravitational regions of freely propagating AGWs on the spectral plane $$\left( {\omega ,{{k}_{x}}} \right)$$ depending on the temperature gradient was investigated. It is shown that the acoustic and gravitational regions approach each other with a positive temperature gradient, while the distance between them increases with a negative gradient. On the spectral plane, the indicators of the location of the acoustic and gravitational regions of freely propagating AGWs are the dispersion curves of the non-divergent and inelastic horizontal wave modes. The possibility of overlapping the acoustic and gravitational regions of AGWs in a nonisothermal atmosphere was investigated.

Attenuation of Acoustic-Gravity Waves in an Isothermal Atmosphere: Consideration with the Modified Navier-Stokes and Heat-Transfer Equations

Abstract: Within the model of a dissipative isothermal atmosphere, the attenuation of acoustic−gravity waves (AGWs) is studied on the basis of the modified Navier−Stokes and heat-transfer equations. Besides the usually considered velocity gradient, the modification of these equations takes into account the additional transfer of the momentum and energy induced by AGWs due to the density gradient. This results in that additional terms appear in the hydrodynamic equations of motion and heat transfer. Under these assumptions, the local dispersion equation for AGWs in an isothermal dissipative atmosphere, as well as an expression for the damping decrement, is obtained. In the limiting cases of high frequencies (sound waves) and low frequencies (gravitational waves), the nature of the attenuation allows a clear physical interpretation. Special aspects of the time-dependent attenuation for the evanescent acoustic−gravity modes of various types, including the Lamb waves and Brent−Vaisala oscillations, are also considered.

Extremely High Energy (E > 1020 eV) Cosmic Rays: Potential Sources

Abstract: One of the unsolved problems of cosmic ray physics is determining the nature and sources of ultrahigh energy cosmic rays (UHECRs, E > 1018 eV). The high degree of isotropy of the observed UHECR intensity caused mainly by the deviations of the UHECR trajectories in extragalactic and Galactic magnetic fields, as well as the significant uncertainty in their chemical composition (atomic mass), preclude one from tracing the observed events to their sources and finding the mechanisms for their acceleration. There are two ways to reduce the influence of magnetic deflection: by considering events with extremely high energy (EHECR, E > 1020 eV) and taking into account modern models of the Galactic magnetic field to correct its influence on the EHECR trajectory. In this study, the observed arrival directions of EHECRs from the Pierre Auger Observatory (PAO) and Telescope Array (TA) detectors' data are adjusted for the influence of Galactic and random extragalactic magnetic fields. New celestial positions of EHECRs are compared to the samples of potential sources used by the PAO—17 active galactic nuclei (AGNs) with powerful gamma radiation (from the 2FHL catalog) and 23 starburst galaxies (radio-flux-selected)—as well as with samples of 42 radio-galaxies from the parameterized catalog of radio-galaxies and magnetars. Taking into account the energy loss length of the nuclear component (H, He, C, Si, Fe) of EHECRs in the extragalactic environment and the expected typical distances to potential sources (~100 Mpc for H and Si-Fe and ~50 Mpc for He and C), the astrophysical objects that could be sources of relevant events were distinguished in the above samples. The potential acceleration mechanisms in the selected objects are analyzed, and the contribution of possible Galactic sources to the observed EHECR flux is evaluated.

Solar Faculae: Microturbulence as an Indicator of Inclined Magnetic Fields

Abstract: The observations of the solar facula in the Ba II λ 455.403 A line are used to construct a 3D model of the facula area by solving the inverse nonequilibrium radiative transfer problem and to investigate the fine structure of the field of unresolved velocities (microturbulence). New turbulent structures are formed in the layers of the upper photosphere. They are localized mainly between upward and downward flows with the formation of ring-shaped structures of increased turbulence around these flows. The mechanism of magnetic anisotropy of microturbulent velocity is proposed (small-scale eddy-type plasma motions mainly occur in the planes perpendicular to the magnetic field), which explains the height dependence of the field of unresolved velocities. Anisotropy of microturbulence begins to manifest itself in the lower photospheric layers outside the upward and downward flows, while it manifests itself in the higher layers inside these flows. The increase of microturbulence in the layers of the upper photosphere and the lower chromosphere in the areas between matter flows indicates the presence of inclined magnetic fields, which, along with the blurring of its spatial structure, indicates the existence of a magnetic canopy region. Microturbulence can be used as an additional tool for diagnostics of inclined magnetic fields.

Shamakhy Fiber Echelle Spectrograph

Abstract: The high-resolution fiber echelle Cassegrain spectrograph for the 2-m telescope at the Shamakhy Astrophysical Observatory (ShaFES) is described. The optical circuit and the schematic of the suspended part of the spectrograph are presented. The spectrograph operates in two modes with a spectral resolution of 27 500 and 55 000 in the 370–850 nm wavelength range. The results of its testing are analyzed. The results and the procedure of test observations are detailed, and the spectrograph itself and ShaFES observational data are compared with similar instruments and the corresponding experimental data. The spectrograph provides an opportunity to measure spectra of 8m and 10m stars with a signal-to-noise ratio of S/N = 150–200 at λ = 580 nm with a 1-h exposure and resolution of R = 55 000 and 27 500, respectively.

Variations in the Plasma Parameters of the Earth’s Magnetotail during Substorm Initiation

Abstract: A chain of events accompanying the occurrence of a substorm in the Earth’s ionosphere and magnetosphere is considered. Features of geomagnetic pulsations and mechanisms of their generation are indicated. Measurements of magnetic field fluctuations from fluxgate magnetometers, as well as the data on temperature, velocity, and concentration of electrons, and different types of ions from the PEACE and CIS-CODIF experiments of the Cluster-2 space mission, have been analyzed. It was found that a significant increase in temperature, velocity fluctuations, and concentration is observed during the initiation of a substorm that was accompanied by dipolarization (sharp change in the magnetic field configuration from the elongated tail-like force lines to a more dipole structure). A time delay in the heating of protons and oxygen ions, as well as in the concentration variations, was detected. The comparison of wave characteristics for different pressures was carried out using wavelet analysis. The magnetic field pressure, as well as dynamic and thermal pressure for different types of particles, was considered. Pc5 and strong Pc4 pulsations, as well as direct and inverse cascades, were observed in the fluctuations of the magnetic field pressure and thermal pressure of electrons and protons. The results point to a significant role of kinetic effects in the complex chain of processes in the Earth’s magnetosphere during the explosive phase of a substorm.

Velocity Field Diagnostics of the Quiet Sun Using the Lambda-Meter Method: Si I 1082.7 nm Line

Abstract: The validity of the lambda-meter method for determining the quiet Sun velocity field using the Si I 1082.7 nm line is investigated. To this end, the intensity profiles of this line were calculated for the solar disk center by means of NLTE simulations in a three-dimensional model atmosphere describing the small-scale magnetic activity in the quiet solar photosphere. The velocity field recovered using the lambda-meter method from theoretical NLTE profiles of the Si I 1082.7 nm line was compared with the velocity field from the model atmosphere. The influence of atmospheric and instrumental effects on the results is considered. These effects are atmospheric turbulence and light diffraction by telescope aperture, such as VTT, GREGOR, and EST/DKIST. It is shown that, in the case of observations of the Si I 1082.7 nm line on large-diameter telescopes like GREGOR and EST/DKIST with a spatial resolution substantially better than 0.27″, the lambda-meter method provides reliable values of the velocity field for the lower and upper solar photosphere. For the middle photosphere, the correlation between the inferred and the real velocities is worse, particularly when using the smaller diameter telescopes like VTT. Under a poor spatial resolution exceeding 2″, information about the velocity field can be obtained only for the uppermost photospheric layers. For this case, the lambda-meter velocities turn out to be noticeably smaller than the real values.

The Influence of Solar Activity on Discoveries of Comets from Different Classes

Abstract: —The paper deals with the distribution of discovery dates of comets through phases of the 11‑year cycle of solar activity (SA). Four groups of comets are considered: long-period comets (LPCs) with an orbital period exceeding 200 yr, periodic comets (PCs) of Jupiter’s family, LPCs with a weak absolute brightness, and a group of LPC with perihelia near the plane perpendicular to the ecliptic. The analysis covers the comets found before the beginning of cycle 24. The earlier conclusion on the difference between PCs and LPCs has been confirmed. It has been determined that a single maximum in the PCs distribution corresponds to the postmaximum epoch of SA. In the weak LPCs, this maximum is absent. The distribution of the isolated group of LPCs with respect to SA is also different. In all of the cases, the decay period of cycles dominates the discoveries of comets.

Statistical Analysis of Infrasonic Parameters Generated by the Chelyabinsk Meteoroid

Abstract: The passage of the Chelyabinsk meteoroid generated a wide variety of physical effects in all subsystems in the Earth–atmosphere–ionosphere–magnetosphere system. Earlier studies have been conducted in order to examine the Chelyabinsk meteoroid’s effects in the atmosphere, ionosphere, and the geomagnetic field. Particular attention has been given to the features of the infrasound signal generated by the Chelyabinsk meteoroid. At the same time, the results of the statistical analysis of infrasonic parameters are absent in the literature. The purpose of this paper is to construct scatter diagrams for basic infrasonic parameters of the signal propagating globally (such as signal-to-noise ratios, time lags, celerity, time durations, amplitudes, and periods per cycle) depending on either the distance between the infrasound source and the sensor or the source back-azimuth as well as to fit respective regression lines. The data have been retrieved from 15 infrasound stations of the International Monitoring System (IMS) set up by the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO). On individual occasions, these data have been complemented by the data acquired by the infrasound stations located at the Eurasian geophysical observatories. Scatter diagrams have been constructed for basic parameters of the infrasonic signal propagating globally. The estimated regression lines superimposed on the scatter diagrams of these parameters versus distance or back-azimuth are shown. Estimates of the infrasound signal celerity (approximately 280 m/s) and tropospheric and stratospheric wind speed (approximately 30 m/s) averaged over all propagation paths have been determined. The advantages and disadvantages of the proposed regression lines are discussed.

Integrated Characteristics of SDSS DR14 Star-Forming Galaxies with Extremely Low Oxygen Abundances

Abstract: Integrated characteristics of a sample of 66 star-forming galaxies with extremely low oxygen abundances from the SDSS Data Release 14 are studied. The oxygen abundances were determined by the direct Te method for 42 galaxies with detected [O III] 436.3 nm emission lines and by the strong-line method for the remaining galaxies. Derived abundances 12 + log (O/H) fall within the 6.97–7.52 range and are, on average, four times lower than the corresponding values for a large comparison sample of compact star-forming galaxies from the SDSS. Stellar masses and Hβ luminosities for both samples were derived from SDSS spectra with a small spectroscopic aperture (2–3 arcsec in diameter). In order to determine their values for the entire galaxy, aperture corrections taking radiation outside the spectroscopic slit into account were introduced. Stellar masses and luminosities in the optical range are 100 times lower than the corresponding values for the galaxies from the comparison sample. At fixed values of luminosity and stellar mass, these galaxies have lower oxygen abundances in the oxygen abundance–luminosity and oxygen abundance–stellar mass diagrams than the galaxies from the main SDSS sample. This offset is likely caused by accretion of unenriched intergalactic gas, which reduces the oxygen abundance in the galactic interstellar medium. The majority of galaxies with extremely low oxygen abundances were detected in the mid-infrared range by the WISE space telescope. Color index W1 – W2, where W1 and W2 are the magnitudes at a wavelength of 3.4 and 4.6 μm, of these galaxies corresponds to the values typical for stellar emission and/or free-free ionized gas emission. The low ultraviolet luminosity, which is the main source of dust heating in star-forming galaxies, thus eliminates the possibility that warm and hot dust is present.

Dynamics of magnetic structures during the magnetospheric substorm

Abstract: The Earth’s magnetosphere and the ambient interplanetary environment can create favorable conditions for the nonlinear process of energy release in the form of changes in the topology of the magnetic field and current systems, particle acceleration, wave generation, and sharp gradients in the parameters inherent to a substorm phenomenon. Initially, early studies substantiated the role of variations in the solar wind parameters as a key factor responsible for the onset of a magnetospheric substorm; however, this factor was later shown not to be decisive. Over several decades, continuously improving methods for designing measurement tools and analyzing data helped to identify the processes that accompany the substorm phenomenon and describe them both qualitatively and quantitatively. However, there is no consensus in understanding the scenario of substorm development stepwise. The purpose of the research is to determine the propagation and orientation features of transients (fronts) in the current sheet of the Earth’s magnetotail during a substorm. To do this, the magnetic field measurements obtained by the four spacecraft of the Cluster II mission for July 20, 2013, are analyzed. During this event, spacecraft were located on the night side of the Earth’s magnetosphere and recorded changes in the geomagnetic field during the magnetospheric substorm. We used the single-spacecraft method for finding the minimum variance of the magnetic field and multispacecraft timing analysis involving cross-correlation of time series. The first method allows finding the direction of the normal to the structure under study; the second method makes it possible to find the direction and absolute value of its propagation velocity. The results of the study show that, with the development of substorms, the fronts that move towards the Earth exhibit a decrease in the propagation velocity and a significant degree of curvature. The first effect (a decrease in the propagation velocity of the fronts) indicates a decrease in the energy reserve of the current sheet for the generation of such transients, and the second effect (a significant degree of curvature) indicates the azimuthal localization of the front.

Two-Frequency Acoustic-Gravitational Waves and Simulation of Satellite Measurements

Abstract: The theory of acoustic gravity waves (AGW) considers free disturbances of the atmosphere within the framework of a single-frequency approach. In this case, the theory implies the existence of two separate types of waves with different natural frequencies: acoustic and gravitational. In the single-frequency approach, wave fluctuations of density, temperature, and velocity are related to each other through the spectral characteristics of the wave, and these relationships are unchanged. However, satellite observations of AGW parameters cannot always be explained within the framework of a single-frequency approach. This paper presents a two-frequency approach to studying AGWs using the model of two coupled oscillators. It is shown that the perturbed movements of the elementary volume of the medium occur simultaneously at two natural frequencies. In this case, the connections between the wave fluctuations of the parameters are determined by the initial conditions, which can be arbitrary. Solutions in real functions for an isothermal atmosphere are obtained. The conditions under which single-frequency AGWs are obtained from the general two-frequency solution are investigated. The AGW waveforms measured from the satellite for velocities and displacements in single-frequency and dual-frequency modes are numerically simulated. The results of simulating two-frequency AGWs agree with the data of satellite measurements. Two-frequency AGWs are not always implemented at two different frequencies. It is shown that, when the frequencies approach each other, the beat effect occurs and two closely related modes become indistinguishable. At the same wavelength, they have one center frequency and one phase velocity. The main feature of the two-frequency approach to the study of AGW is the expansion of the relationships between the wave parameters of the medium. This makes it possible to achieve satisfactory agreement of the model waveforms with the data of satellite measurements. Thus, the use of a two-frequency AGW treatment opens up new possibilities in the interpretation of experimental data.

Investigation and Analysis of Spatiotemporal Instability of the Earth's Atmosphere Based on Real-Time GNSS Data Processing

Abstract: One of the options for the practical application of GNSS technology, in addition to geodetic and navigation needs, is remote sensing of the atmosphere by radio signals from navigation satellites in order to improve the quality and detail of weather forecasts. The propagation of a radio signal from GNSS satellites to a ground receiving device (GNSS receiver) through a neutral atmosphere is accompanied by a decrease in the phase velocity of the radio waves (additional atmospheric delays). This is due to the presence of nitrogen, oxygen, carbon dioxide, and water vapor molecules in the atmosphere. Therefore, measurements of the additional delay of the radio signal in the atmosphere (tropospheric delay) provide information on the integral properties of the atmosphere along the propagation path of the radio signal. As a result of the primary processing of the GNSS measurement results, the distances from the observation station to GNSS satellites are determined. Secondary processing of GNSS measurements consists in solving a navigation problem and provides information on the location of the station. In order to obtain meteorological information, it is necessary to develop special methods of secondary data processing based on solving inverse problems. The combination of primary and secondary data (processing) along with meteorological information makes it possible to obtain a global model of the atmosphere in near-real time. The efficiency of this approach, the complete automation, and the absence of consumables during remote sensing provide opportunities for the widespread implementation of operational monitoring of the state of the atmosphere in order to improve the data’s detail and accuracy of regional short-term weather forecasts. Currently, due to cross-border cooperation with European countries in conducting joint GNSS observations in the UA-EUPOS/ZAKPOS network of stations, we are able to have an accurate, dense, and continuous sampling of tropospheric delay values, which allows us to determine and predict the dynamics of atmospheric changes in real time. The main goal of the work is to study the spatio-temporal instability of the atmosphere over an area covered by active reference stations. The results of the study can be used to improve the quality of weather prediction.

Helium Burning Duration for Stars of Populations I–III

Abstract: Generalized fitting formulas have been obtained describing the dependence “helium burning time–mass of zero-age stars” for stars belonging to populations I–III and having the corresponding masses and elemental composition. The approximation has been performed for nonrotating and rotating stars. The regularities in the obtained dependences have been revealed on the content Z of heavy chemical elements (ranging from 0 to 0.1), which include characteristic values for stellar populations I–III in the presence or absence of axial rotation.

On the Radiative Relaxation Time for the Hydrogen–Helium Atmosphere Estimated from Changes in the Activity Factor of Jupiter’s Hemispheres

Abstract: The subsolar point on Jupiter’s magnetosphere changes its position by an angle of approximately 26° over the orbital period of Jupiter, which induces seasonal variations in physical and optical characteristics of the planetary atmosphere. At the time close to the summer solstice for the northern hemisphere, Jupiter is in perihelion. Consequently, due to the significant orbital eccentricity, the energy influx into the atmosphere in the northern hemisphere is 21% larger than that in the southern one. This leads to the asymmetry in the meridional distribution of the reflectance of visible clouds. Analysis of the results of photometric observations of Jupiter for 1960–2019 showed that the ratio AJ = BN/BS adequately describes the activity of atmospheric processes on Jupiter, which shows periodic increases in brightness at tropical and temperate latitudes in the southern and northern regions by turn during one orbital period of Jupiter. The response of the atmosphere to changes in the irradiation by the Sun does not occur instantaneously but with some delay. The results of observations of Jupiter in the visible range in 1960–1995 and 2012–2019 show a synchronous delay of 3.4 year (τR ≈ 1.07 × 108 s) in response to the 21% change in the irradiation of different hemispheres when the planet is orbiting the Sun. In 1995–2012, the discrepancy caused by the orbital motion of the planet was observed between the behavior of AJ, the solar activity index Sn, and Jupiter’s regime of exposure to the Sun. Variations associated with the influence of solar activity are mainly induced by significant changes in the ultraviolet radiation of the Sun. These changes first affect the energetics of the upper atmosphere of Jupiter, after which they are indirectly transmitted into the troposphere, sometimes reducing the value of the relaxation constant τR to ~2.5 years. Since 2012, the behavior of the time dependence of AJ, the index of solar activity, and the irradiation regime of Jupiter due to its orbital motion have become consistent again. The periodicity in changes of the photometric characteristics of the northern and southern hemispheres of Jupiter were also restored.

Verification of Einstein’s Formula for Gravitational Deflection of Light Using Observations of Galactic Microlensing

Abstract: General relativity (GR) has a solid experimental base. However, the emergence of new experimental capabilities and independent observational information stimulates continuing tests of general relativity. The purpose of this work is to evaluate the potential of gravitational microlensing of distant sources on the stars of our Galaxy and to verify Einstein’s formula of gravitational refraction. This effect has been repeatedly tested in the Solar System in high-accuracy experiments with the propagation of radio waves, when the measurements are most effective for the distances from the signal trajectory to the Sun on the order of several solar radii. In the case of galactic microlensing, a quite different type of observational data and other characteristic distances are used that are determined in the high magnification events by the Einstein ring radii, which is typically of the order of 1 AU. Although the gravitational deflections of light by stars are very small and currently practically inaccessible by direct measurements, nonetheless, due to the large distances to the microlenses, the radiation flux from the source in strong microlensing events can increase several times. To verify Einstein’s formula, a more general dependence of the beam deflection angle $$\alpha \propto 1/{{p}^{{1 + \varepsilon }}}$$ on its impact distance p relative to the deflector is considered and, accordingly, the equations of gravitational lensing are modified. The challenge is to limit e based on observational data. The Early Warning System data obtained in 2018 within the Optical Gravitational Lensing Experiment (OGLE) ( http://ogle.astrouw.edu.pl/ogle4/ ews/2019/ews.html ) was used. A sample of 100 light curves from the data obtained by the OGLE group in 2018 was formed. Each light curve was fitted as part of a modified model of gravitational lensing with parameter e. As a result, 100 values of e and estimates of their variances were obtained. It was found that the mean value of e does not contradict GR within the limits of a one percent standard deviation. In the future, using a larger number of light curves will allow one to hope for a significant decrease in the error of e due to statistical averaging.