Kinematics and Physics of Celestial Bodies最新文献

A solar eclipse (SE) provides a researcher with a rare opportunity to follow the dynamics of the Earth’s system (its shells)—the atmosphere, the ionosphere, and the magnetosphere—and variations in the geophysical fields over an interval of a few hours. Different solar eclipses induce significantly different disturbances in this system. The parameters of these disturbances depend on the onset time of a solar eclipse, the state of space weather, the season, the solar cycle phase, the geographic coordinates, and the degree of the solar disk occultation during a solar eclipse. It should be kept in mind that each of the SEs exhibits its own individual characteristics. The purpose of this paper is to analyze the results of ionosonde observations of the ionospheric disturbances accompanying the SE above the city of Kharkiv on June 10, 2021. At the city of Kharkiv, the maximal observed magnitude of the SE was М_max ≈ 0.11 (more precisely, 0.112) and the relative area of the solar disk occultation was А_max ≈ 4.4%. The eclipse started at 10:42 UT (13:42 LT) and ended at 12:12 UT (15:12 LT). The maximal magnitude was observed at 11:28 UT (14:28 LT). To study the features of variations in the virtual heights and the frequencies, we used a digital ionosonde located at the Radio Physical Observatory of the V. N. Karazin Kharkiv National University. The analysis of the space weather showed that, during the SE, as well as at the reference time intervals on June 6 and 9, 2021, the space weather conditions were favorable for observing wave disturbances, which is evidenced by the index value K_p ≈ 0.3. The frequency and altitude characteristics of the ionosphere obtained by vertical sounding were analyzed, and the features of the ionospheric processes, which accompanied the partial SE but were absent on the reference day, were determined. During the SE, wave activity in the ionosphere became stronger. The wave trains, which were observed at an altitude of the F₂ layer maximum, had periods of 5 and 14 min, while the relative amplitudes of oscillations in the electron density were 0.6 and 1.25%, respectively. At an altitude of 240 km, the relative amplitude of waves with a period of ~14 min increased by 3%. The 14-min period pertains to the atmospheric gravitaty waves, while the 5-min period pertains to the waves of electromagnetic nature. A sharp and considerable increase (from 380 to 560 km) in the virtual height of the radio wave reflection from the F₂ region was observed close to the moment of the greatest SE magnitude. A weak decrease (by less than 3.3%) in the electron density, which lagged behind the maximal eclipse magnitude by 12.5 min, was detected. The rates of the electron loss (1.33 × 10^–3 s^–1) and the ion production (3 × 10⁸ m^–3s^–1) were estimated.

Actinium is a radioactive element that has an isotope ²²⁷Ac with the longest half-life of 21.772(3) years. It is the third element in the actinoid group, in addition to thorium and uranium, the abundance of which can be studied in the atmospheres of stars. Its presence in the atmosphere of a particular star primarily indicates some mechanism of its production. The first studies of the actinium absorption lines in the spectra of certain stars showed that the appearance of actinium in their spectrum is associated with the presence of deformation of strong lines, such as hydrogen lines and sodium doublet lines. In some cases, profiles of strong lines contain emission components. In the search for actinium absorption lines in the stellar spectra, attention was focused on such class of stars as Cepheids, which are characterized by deformation of strong lines due to pulsations. The absorption lines of actinium were studied in the spectral interval of 378.0–887.7 nm for the runaway star and Cepheid HIP13962 using the spectra obtained in 2014 with a 1.8-m telescope at Bohyunsan Optical Astronomical Observatory (BOAO, South Korea) with a spectral resolution greater than R = 80 000. The archived HIP13962 spectrum for 1995 in the wavelength range of 400.0–680.0 nm with a spectral resolution R = 42 000, which was obtained with the 1.93-m telescope of the Haute Provence Observatory (France), was also used. The modeling showed that the actinium abundance in the atmosphere of HIP13962 log N(Ac) = –1.2 on the hydrogen scale log N(H) = 12.0, with the model atmosphere T_eff = 5930 K, log g = 1.0, V_micro = 6 km s^–1. This value turns out to be 0.2 more at an increase in the effective temperature T_eff = 6250 K: logN(Ac) = –1.0 on the hydrogen scale logN(H) = 12.0.

The Doppler line shifts in the spectra of the Sun and stars with effective temperatures from 4800 to 6200 K were measured and the average convective (granulation) velocities were estimated. The absolute scale of the line shifts for the stars was established on the basis of the derived dependence of the shifts of solar lines on optical depth. For FGK solar-type stars, curves of convection velocities as a function of the altitude in the atmosphere in a large range of altitudes from 150 to 700 km were obtained for the first time. All these curves indicate a decrease in blue shifts with altitude, which means that the granulation velocities through the photosphere slow down to zero. In the lower chromosphere, red shifts of strong Mg I lines are observed, which indicate a change in the direction of granulation velocities to the opposite and confirm the effects of reversal of granulation at altitudes above 600 km. In cooler K stars, granulation shifts change with altitude on average from –150 to 100 m/s, while they change more sharply in hotter FG stars from –700 to 300 m/s. The gradient of the line shift curves increases with an increase in the effective temperature and a decrease in gravity, metallicity, and age of the star. The convective velocity of the star averaged over all analyzed altitudes increases from –90 to –560 m/s from colder to hotter stars. It correlates with macroturbulence, asymmetry of spectral lines, and the rotation velocity of the star. We also obtained the radial velocities of the stars and compared them with the SIMBAD data. Large deviations of –21 050 and 1775 m/s were found for the stars HD 102361 and HD 42936, respectively. For the rest of the stars, the deviation does not exceed ±340 m/s, which is probably associated with the use of an average granulation velocity of –300 m/s in the SIMBAD data. Our analysis has shown that the average granulation velocity is not the same for solar-type stars. It is lower in colder stars and higher in hotter stars than the Sun. Therefore, determination of the radial velocities needs to take into account the individual granulation velocities of stars.

Continuous monitoring of artificial space objects requires periodic quality control of observational data. Estimating the internal accuracy of observations in the form of an RMS error of positions makes it possible to monitor and detect outliers in primary data array. For artificial satellites of the Earth, the orbital elements calculated at the Research Institute Nikolaev Astronomical Observatory (RI NAO) can be externally compared with the data of the International Laser Ranging Service (ILRS) or the Global Navigation Satellite System (GNSS). Such a comparison makes it possible to detect time synchronization problems and to identify and evaluate systematic errors. At the RI NAO, regular observations of artificial satellites in different orbits using several telescopes have been carried out for more than 10 years, and a catalog of orbital elements in the two-line element (TLE) format is maintained. The software for calculating orbital elements has been developed in cooperation with the Astronomical Observatory of the Odessa National University. This article presents the analysis of the processing results of an array of observations from 149 geostationary satellites (GSS’s). The observations have been made during 2020…2021 using the RI NAO telescope complex. Time synchronization has been provided by the Resolution-T GPS receiver with an RMS error of 40 ns. All GSS observations have been carried out using the combined observation method developed at the RI NAO. A total of 134 461 GSS positions have been obtained for which the residual O–C differences with respect to the orbit calculated at the RI NAO have been determined. The RMS error of the GSS positions in the apparent magnitude range 9^m…13^m is 0.5″ in right ascension and declination. A comparison of the GSS orbital positions calculated from the RI NAO orbital elements and the ILRS website data shows that the differences between the corresponding geocentric Cartesian coordinates at the start of the prediction are dX = 0.72 km, dY = –0.52 km, and dZ = 1.28 km.

The features of the spatial distribution of atmospheric gravity waves (AGW) in the polar thermosphere of the Earth are investigated. The research is based on data from direct satellite measurements of the parameters of the neutral atmosphere. According to satellite data, the amplitudes of AGWs that are systematically observed in the polar regions of both hemispheres are usually several times higher than the amplitudes of these waves in the middle and low latitudes. At the same time, the polar AGWs of large amplitudes are recorded against the background of high-speed spatially inhomogeneous wind flows, which indicates their possible amplification caused by interaction with the wind. Based on the analysis of measurement data on the Dynamics Explorer 2 satellite, the relationship between the spatial distribution of the atmospheric gravitational waves and the auroral oval has been revealed. On a large volume of experimental data, seasonal patterns of the distribution of the wave field over the Antarctic and the Arctic have been established. A comparative analysis of the features of the AGWs in the polar thermosphere of both hemispheres for the conditions of the polar day and polar night has been carried out. Some differences in the distribution of the AGWs were noted depending on the Kp-index. It has been suggested that the observed seasonal features of the AGW distribution and its dependence on the level of geomagnetic activity are associated with the restructuring of the polar wind circulation when the conditions of solar illumination and geomagnetic conditions change.

An analysis is presented of the scientific research accomplished by Ukrainian astronomer Mykola Evdokymov, a specialist in the field of astrometry. The astronomer’s main works, carried out using a Repsold meridian circle, are dedicated to determining stellar parallaxes, the positions of zodiacal and faint circumpolar stars, and the positions of large planets. At Kharkiv Astronomical Observatory, Evdokymov conducted systematic observations of the following objects and phenomena: solar and lunar eclipses, including as a member of the observatory’s expeditions during the total solar eclipses of 1914 and 1936; comets (Halley, Delavan, Stearns, Pons–Winnecke); and meteor showers. He participated in determining the positions of reference stars for the asteroid (433) Eros. He conducted systematic studies of the meridian circle, developed new astronomical instruments, organized the functioning of a time service at the observatory, and carried out the determination of star declinations by measuring the sums and differences of the zenith distances of star pairs by the Sanders–Raymond method (using a meridian circle and a transit instrument).

The data acquired at ten geomagnetic observatories (Paratunka, Magadan, Yakutsk, and Khabarovsk (the Russian Federation); Memambetsu, Kanoya, and Kakioka (Japan); Cheongyang (Republic of Korea); Shumagin and College (USA)) during the Kamchatka meteoroid event of December 18, 2018, and on the reference days of December 17 and 19, 2018, have been used to analyze temporal variations in the geomagnetic field components. The distance r from the observatories to the site of explosive energy release by the meteoroid varied from 1.001 to 4.247 Mm. The passage of the Kamchatka meteoroid through the magnetosphere and atmosphere was accompanied by variations mainly in the H geomagnetic field component. The magnetic effect from the magnetosphere was observed to occur twice, 51 and 28 min prior to the meteoroid explosion; the amplitude of the disturbances in the geomagnetic field did not exceed 0.2–1 nT, and the durations were observed to be approximately 20 and 10 min, respectively. Alternating peaks in the level of the H component were observed to lag behind the meteoroid explosion by 8 to 13 min for r from 1.001 to 4.247 Mm. The amplitude of the oscillations varied with increasing r from ~0.5 to ~0.1 nT, while the duration of the magnetic effect from the ionosphere varied in the 16–25-min range for all distances. The apparent speed of propagation in this group of disturbances that were of MHD nature was observed to be approximately 10 km/s. In the second group of disturbances, the time lag increased with increasing distance within the distance range mentioned above from 56 to 218 min. The duration of the disturbance was approximately 16–65 min, the apparent speed was 336 m/s, and the period was 5–10 min. This disturbance in the magnetic field was caused by an atmospheric gravity wave propagating from the meteoroid explosion. The theoretical models for the magnetic effects observed are presented and theoretical estimates are performed. The observations are in agreement with the estimates.

The results of spectropolarimetric and filter observations of the facular region in the lines Fe I 1564.3, Fe I 1565.8 nm, Ba II 455.4 nm, and Ca II H 396.8 nm obtained near the center of the solar disk at the German Vacuum Tower Telescope (Tenerife, Spain) are discussed. It is shown that the facular contrast at the center of the Ca II H line increases more slowly as the magnetic field strength increases and, then it begins to decrease if the field increases further. It is concluded that the reason for such behavior is the nonlinear height dependence of the line source function due to the deviation from the local thermodynamic equilibrium. It is found that waves propagating both upward and downward can be observed in any area of the facula, regardless of its brightness. In bright areas with a strong magnetic field, upward waves predominate, while downward waves are more often observed in less bright areas with a weak field. It is shown that the facular contrast measured at the center of the Ca II H line correlates with the power of wave velocity oscillations. In bright areas, it increases with the power regardless of the direction in which the waves propagate. In facular regions with decreased brightness, the opposite dependence is observed for both types of waves. In turn, the power of wave velocity oscillations is sensitive to the field strength magnitude. In the magnetic elements of the facula with increased brightness, the stronger the field, the higher the power of oscillations of both upward and downward waves. In areas with decreased brightness, the inverse dependence is observed. It is concluded that the contrast increase with the increase in the power of wave velocity oscillations observed in bright areas of the facula can be considered as evidence that these areas look bright not only because of the Wilson depression but also because of the heating of the solar plasma by the waves.

A solar eclipse (SE) pertains to rare high-energy natural phenomena. For instance, a change in the internal (thermal) energy of the air in a layer only 100 m in height attains 10¹⁸ J while the power of the process is on the order of terawatts. The energy of the processes produced by the SE in the upper atmosphere and geospace is significant. For instance, the thermal energy of the ionospheric plasma in a volume of ~10¹⁹ m³ decreases by 10¹¹ J. The magnetic field in a volume of ~10²¹ m³ decreases by 50 nT, and its energy by 10¹⁵ J. SEs are accompanied by disturbances in all subsystems of the Earth–atmosphere–ionosphere–magnetosphere system. Disturbances in the upper atmospheric and ionospheric parameters act to inevitably produce geomagnetic field variations. At present, geophysicists have no consensus on how SE manifests itself in the geomagnetic field. The available data are inconsistent. Most of the researchers believe that the geomagnetic effect of SE exists. In some cases, the temporal variations in the geomagnetic field, as a whole, repeat the changes in the illumination of the Earth’s surface; in other cases, they may be ahead or delayed by ~1 hour in relation to the changes in illumination. Most often, the geomagnetic effect is studied in the region of the total SE where it should be the most pronounced. The further the observatory is located from the umbra, the more difficult it is to relate the magnetic variations to the SE. Finding the response of the geomagnetic field to the SE is a complicated task. A possible response is “masked” by variations of another nature. Moreover, the magnitude and sign of the geomagnetic field disturbance significantly depend on the state of space weather, season, local time, location of the magnetic observatory, and, of course, the magnitude of the eclipse. Therefore, the study of the effect of SEs on the geomagnetic field remains an important task. The purpose of this study is to present the results of analysis of temporal variations in the geomagnetic field observed by the International Real-Time Magnetic Observatory Network (INTERMAGNET) during the SE of June 10, 2021. The main feature of this eclipse was that the SE was annular (maximum magnitude M_max ≈ 0.943). The annular SE occurred on June 10, 2021 with a commencement time 08:12:20 UT over Canada. The Moon’s shadow moved across the Atlantic Ocean, Greenland, the Arctic Ocean, the North Pole, and the northern parts of Europe and Asia. A partial SE occurred in Mongolia and China, and it ceased at 11:33:43 UT. The annularity was observed from 10:33:16 to 10:36:56 UT over Greenland. The analysis of the geomagnetic effect was based on the INTERMAGNET database. The data were processed with 1-min temporal resolution and 0.1-nT level resolution, and temporal variations in the X, Y, and Z components recorded at 15 magnetic observatories were studied