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- The Korean Space Science Society (The Korean Astronomical Society)
- 계간 (Quarterly)
- ISSN : 1225-052x (ISSN : 1225-052x)
1225-052x
- DB구축현황 : 1,255건 (DB Construction : 1,255 Articles)
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141
- Kwak, Young-Sil
- Journal of astronomy and space sciences
- 36, n.3
- pp.159-168
- 2019
- 원문 바로보기
In solstices during the solar minimum, the hemispheric difference of the equatorial ionization anomaly (EIA) intensity (hereafter hemispheric asymmetry) is understood as being opposite in the morning and afternoon. This phenomenon is explained by the temporal variation of the combined effects of the fountain process and interhemispheric wind. However, the mechanism applied to the observations during the solar minimum has not yet been validated with observations made during other periods of the solar cycle. We investigate the variability of the hemispheric asymmetry with local time (LT), altitude, season, and solar cycle using the electron density taken by the CHAllenging Minisatellite Payload satellite and the global total electron content (TEC) maps acquired during 2001-2008. The electron density profiles provided by the Constellation Observing System for Meteorology, Ionosphere, and Climate satellites during 2007-2008 are also used to investigate the variation of the hemispheric asymmetry with altitude during the solar minimum. During the solar minimum, the location of a stronger EIA moves from the winter hemisphere to the summer hemisphere around 1200-1400 LT. The reversal of the hemispheric asymmetry is more clearly visible in the F-peak density than in TEC or in topside plasma density. During the solar maximum, the EIA in the winter hemisphere is stronger than that in the summer hemisphere in both the morning and afternoon. When the location of a stronger EIA in the afternoon is viewed as a function of the year, the transition from the winter hemisphere to the summer hemisphere occurs near 2004 (yearly average F10.7 index = 106). We discuss the mechanisms that cause the variation of the hemispheric asymmetry with LT and solar cycle.
142
- Choi, Jin
- Journal of astronomy and space sciences
- 36, n.1
- pp.35-43
- 2019
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The Optical Wide-field patroL-Network (OWL-Net) is a global optical network for Space Situational Awareness in Korea. The primary operational goal of the OWL-Net is to track Low Earth Orbit (LEO) satellites operated by Korea and to monitor the Geostationary Earth Orbit (GEO) region near the Korean peninsula. To obtain dense measurements on LEO tracking, the chopper system was adopted in the OWL-Net's back-end system. Dozens of angle-only measurements can be obtained for a single shot with the observation mode for LEO tracking. In previous work, the reduction process of the LEO tracking data was presented, along with the mechanical specification of the back-end system of the OWL-Net. In this research, we describe an integrity assessment method of time-position matching and verification of results from real observations of LEO satellites. The change rate of the angle of each streak in the shot was checked to assess the results of the matching process. The time error due to the chopper rotation motion was corrected after re-matching of time and position. The corrected measurements were compared with the simulated observation data, which were taken from the Consolidated Prediction File from the International Laser Ranging Service. The comparison results are presented in the In-track and Cross-track frame.
143
- Doikov, Dmytry N.
- Journal of astronomy and space sciences
- 36, n.1
- pp.21-33
- 2019
- 원문 바로보기
This paper focuses on the interpretation of radiation fluxes from active galactic nuclei. The advantage of positron annihilation spectroscopy over other methods of spectral diagnostics of active galactic nuclei (therefore AGN) is demonstrated. A relationship between regular and random components in both bolometric and spectral composition of fluxes of quanta and particles generated in AGN is found. We consider their diffuse component separately and also detect radiative feedback after the passage of high-velocity cosmic rays and hard quanta through gas-and-dust aggregates surrounding massive black holes in AGN. The motion of relativistic positrons and electrons in such complex systems produces secondary radiation throughout the whole investigated region of active galactic nuclei in form of cylinder with radius R= 400-1000 pc and height H=200-400 pc, thus causing their visible luminescence across all spectral bands. We obtain radiation and electron energy distribution functions depending on the spatial distribution of the investigated bulk of matter in AGN. Radiation luminescence of the non-central part of AGN is a response to the effects of particles and quanta falling from its center created by atoms, molecules and dust of its diffuse component. The cross-sections for the single-photon annihilation of positrons of different energies with atoms in these active galactic nuclei are determined. For the first time we use the data on the change in chemical composition due to spallation reactions induced by high-energy particles. We establish or define more accurately how the energies of the incident positron, emitted <TEX>${\gamma}-quantum$</TEX> and recoiling nucleus correlate with the atomic number and weight of the target nucleus. For light elements, we provide detailed tables of all indicated parameters. A new criterion is proposed, based on the use of the ratio of the fluxes of <TEX>${\gamma}-quanta$</TEX> formed in one- and two-photon annihilation of positrons in a diffuse medium. It is concluded that, as is the case in young supernova remnants, the two-photon annihilation tends to occur in solid-state grains as a result of active loss of kinetic energy of positrons due to ionisation down to thermal energy of free electrons. The single-photon annihilation of positrons manifests itself in the gas component of active galactic nuclei. Such annihilation occurs as interaction between positrons and K-shell electrons; hence, it is suitable for identification of the chemical state of substances comprising the gas component of the investigated media. Specific physical media producing high fluxes of positrons are discussed; it allowed a significant reduction in the number of reaction channels generating positrons. We estimate the brightness distribution in the <TEX>${\gamma}-ray$</TEX> spectra of the gas-and-dust media through which positron fluxes travel with the energy range similar to that recorded by the Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA) research module. Based on the results of our calculations, we analyse the reasons for such a high power of positrons to penetrate through gas-and-dust aggregates. The energy loss of positrons by ionisation is compared to the production of secondary positrons by high-energy cosmic rays in order to determine the depth of their penetration into gas-and-dust aggregations clustered in active galactic nuclei. The relationship between the energy of <TEX>${\gamma}-quanta$</TEX> emitted upon the single-photon annihilation and the energy of incident electrons is established. The obtained cross sections for positron interactions with bound electrons of the diffuse component of the non-central, peripheral AGN regions allowed us to obtain new spectroscopic characteristics of the atoms involved in single-photon annihilation.
144
- Kim, Young-Rok
- Journal of astronomy and space sciences
- 36, n.4
- pp.293-306
- 2019
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In this study, the observational arc-length effect on orbit determination (OD) for the Korea Pathfinder Lunar Orbiter (KPLO) in the Earth-Moon Transfer phase was investigated. For the OD, we employed a sequential estimation using the extended Kalman filter and a fixed-point smoother. The mission periods, comprised between the perigee maneuvers (PM) and the lunar orbit insertion (LOI) maneuver in a 3.5 phasing loop of the KPLO, was the primary target. The total period was divided into three phases: launch-PM1, PM1-PM3, and PM3-LOI. The Doppler and range data obtained from three tracking stations [included in the deep space network (DSN) and Korea Deep Space Antenna (KDSA)] were utilized for the OD. Six arc-length cases (24 hrs, 48 hrs, 60 hrs, 3 days, 4 days, and 5 days) were considered for the arc-length effect investigation. In order to evaluate the OD accuracy, we analyzed the position uncertainties, the precision of orbit overlaps, and the position differences between true and estimated trajectories. The maximum performance of 3-day OD approach was observed in the case of stable flight dynamics operations and robust navigation capability. This study provides a guideline for the flight dynamics operations of the KPLO in the trans-lunar phase.
145
- Hong, Junseok
- Journal of astronomy and space sciences
- 36, n.3
- pp.121-131
- 2019
- 원문 바로보기
The ionospheric mid-latitude trough (IMT) is the electron density depletion phenomenon in the F region during nighttime. It has been suggested that the IMT is the result of complex plasma processes coupled to the magnetosphere. In order to statistically investigate the characteristics of the IMT, we analyze topside sounding data from Alouette and ISIS satellites in 1960s and 1970s. The IMT position is almost constant for seasons and solar activities whereas the IMT depth ratio and the IMT feature are stronger and clearer in the winter hemisphere under solar minimum condition. We also calculated transition heights at which the densities of oxygen ions and hydrogen/helium ions are equal. Transition heights are generally higher in daytime and lower in nighttime, but the opposite aspects are seen in the IMT region. Utilizing the Incoherent Scatter Radar (ISR) electron temperature measurements, we find that the electron temperature in the IMT region is enhanced at night during winter. The increase of electron temperature may cause fast transport of the ionospheric plasma to the magnetosphere via ambipolar diffusion, resulting in the IMT depletion. This mechanism of the IMT may work in addition to the simply prolonged recombination of ions proposed by the traditional stagnation model.
146
- Song, Young-Joo
- Journal of astronomy and space sciences
- 36, n.3
- pp.213-223
- 2019
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This paper analyzes delta-Vs to maintain an extremely low altitude on the Moon and investigates the possibilities of performing a CubeSat mission. To formulate the station-keeping (SK) problem at an extremely low altitude, current work has utilized real-flight performance proven software, the Systems Tool Kit Astrogator by Analytical Graphics Inc. With a high-fidelity force model, properties of SK maneuver delta-Vs to maintain an extremely low altitude are successfully derived with respect to different sets of reference orbits; of different altitudes as well as deadband limits. The effect of the degree and order selection of lunar gravitational harmonics on the overall SK maneuver strategy is also analyzed. Based on the derived SK maneuver delta-V costs, the possibilities of performing a CubeSat mission are analyzed with the expected mission lifetime by applying the current flight-proven miniaturized propulsion system performances. Moreover, the lunar surface coverage as well as the orbital characteristics of a candidate reference orbit are discussed. As a result, it is concluded that an approximately 15-kg class CubeSat could maintain an orbit (30-50 km reference altitude having <TEX>${\pm}10km$</TEX> deadband limits) around the Moon for 1-6 months and provide almost full coverage of the lunar surface.
147
- Jo, Eunbyeol
- Journal of astronomy and space sciences
- 36, n.2
- pp.61-68
- 2019
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We have investigated the variations of sporadic E (Es) layer using the measurements of digisondes at Icheon (<TEX>$37.14^{\circ}N$</TEX>, <TEX>$127.54^{\circ}E$</TEX>, IC) and Jeju (<TEX>$33.4^{\circ}N$</TEX>, <TEX>$126.30^{\circ}E$</TEX>, JJ) in 2011-2018. The Es occurrence rate and its critical frequency (foEs) have peak values in summer at both IC and JJ in consistent with their known seasonal variations at mid-latitudes. The virtual height of the Es layer (h'Es) during equinox months is greater than that in other months. It may be related to the similar variation of meteor peak heights. The h'Es shows the semidiurnal variations with two peaks at early in the morning and late in the afternoon during equinoxes and summer. However, the semi-diurnal variation is not obvious in winter. The semi-diurnal variation is generally thought to be caused by the semi-diurnal tidal variation in the neutral wind shear, whose measurements, however, are rare and not available in the region of interest. To investigate the formation mechanism of Es, we have derived the vertical ion drift velocity using the Horizontal Wind Model (HWM) 14, International Geomagnetic Reference Field, and Naval Research Laboratory Mass Spectrometer and Incoherent Scatter Radar-00 models. Our results show that h'Es preferentially occur at the altitudes where the direction of the vertical ion velocity changes. This result indicates the significant role of ion convergence in the creation of Es.
148
- Hyung, Siek
- Journal of astronomy and space sciences
- 35, n.1
- pp.7-18
- 2018
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We have investigated the intensities and full width at half maximum (FWHM) of the high dispersion spectroscopic N III emission lines of AG Peg, observed with the Hamilton Echelle Spectrograph (HES) in three different epochs at Mt. Hamilton's Lick Observatory. The earlier theoretical Bowen line study assumed the continuum fluorescence effect, presenting a large discrepancy with the present data. Hence, we analyzed the observed N III lines assuming line fluorescence as the only suitable source: (1) The O III and N III resonance line profiles near <TEX>${\lambda}$</TEX> 374 were decomposed, using the Gaussian function, and the contributions from various O III line components were determined. (2) Based on the theoretical resonant N III intensities, the expected N III Bowen intensities were obtained to fit the observed values. Our study shows that the incoming line photon number ratio must be considered to balance at each N III Bowen line level in the ultraviolet radiation according to the observed lines in the optical zone. We also found that the average FWHM of the N III Bowen lines was about <TEX>$5km{\cdot}s^{-1}$</TEX> greater than that of the O III Bowen lines, perhaps due to the inherently different kinematic characteristics of their emission zones.
149
- Lee, Young-Sook
- Journal of astronomy and space sciences
- 35, n.2
- pp.93-103
- 2018
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Non-specular, vertically upward transit, fast-moving radar echoes are observed in the summer polar upper mesosphere near 90 km using 52 MHz VHF radar at Esrange, Sweden. By resolving maximum echo power movement, the unusual meteor trails propagate vertically upward with taking horizontal displacements at an initial speed of 10 km/s exponentially decreasing with increasing height from 85-89 km, lasting for 3.5 sec. Another upward transit is observed as following a downward transit echo target in about ~1 sec, lasting over 5 sec. The upward motion cannot be explained with the dynamics of penetrating meteors or by atmospheric dynamics. The observation proposes that secondary produced plasma jets occurring from meteor trail are possibly responsible for upward fast moving echoes. The long-lasting (3-5 sec), ascending meteor trails at speeds of a few <TEX>$10^4m/s$</TEX> are distinctive from any previous occurrences of meteors or upper atmospheric electrical discharges in the aspect of long-lasting upward/downward motions. This result possibly suggests a new type of meteor-trail leader discharge occurring in the summer polar upper mesosphere and lower thermosphere.
150
- Jeong, Yeuncheol
- Journal of astronomy and space sciences
- 35, n.1
- pp.1-6
- 2018
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The reanalysis of the previously published abundance pattern of mild barium star HD202109 (<TEX>${\zeta}$</TEX> Cyg) and the chemical compositions of 129 thin disk barium stars facilitated the search for possible correlations of different stellar parameters with second ionization potentials of chemical elements. Results show that three valuable correlations exist in the atmospheres of barium stars. The first is the relationship between relative abundances and second ionization potentials. The second is the age dependence of mean correlation coefficients of relative abundances vs. second ionization potentials, and the third one is the changes in correlation coefficients of relative abundances vs. second ionization potentials as a function of stellar spatial velocities and overabundances of s-process elements. These findings demonstrate the possibility of hydrogen and helium accretion from the interstellar medium on the atmospheres of barium stars.