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1984년 ~ 2025년까지 1,249 건의 한국우주과학회지를 계간으로 확인하실 수 있습니다.
- The Korean Space Science Society (The Korean Astronomical Society)
- 계간 (Quarterly)
- ISSN : 1225-052x (ISSN : 1225-052x)
1225-052x
- DB구축현황 : 1,249건 (DB Construction : 1,249 Articles)
총 게시글 1,249건
페이지 12/125
111
- Yushchenko, Alexander V.
- Journal of astronomy and space sciences
- 37, n.3
- pp.157-163
- 2020
- 원문 바로보기
High resolution spectroscopic observation of V1719 Cyg were made at 1.8 meter telescope of Bohyunsan Optical Astronomy observatory in Korea. Spectral resolving power was R=45,000, signal to noise ratio S/N>100. The abundances of 28 chemical elements from carbon to dysprosium were found with the spectrum synthesis method. The abundances of oxygen, titanium, vanadium and elements with Z>30 are overabundant by 0.2-0.9 dex with respect to the solar values. Correlations of derived abundances with condensation temperatures and second ionization potentials of these elements are discussed. The possible influence of accretion from interstellar environment is not so strong as for ρ Pup and other stars with similar temperatures. The signs of accretion are absent. The comparison of chemical composition with solar system r- & s-process abundance patterns shows the enhancement of the photosphere by s-process elements.
112
- Min, Kyungguk
- Journal of astronomy and space sciences
- 37, n.2
- pp.85-94
- 2020
- 원문 바로보기
Equatorial noise, also known magnetosonic waves (MSWs), are one of the frequently observed plasma waves in Earth's inner magnetosphere. Observations have shown that wave amplitudes maximize at the magnetic equator with a narrow extent in their latitudinal distribution. It has been understood that waves are generated from an equatorial source region and confined within a few degrees magnetic latitude. The present study investigates whether the MSW instability and saturation amplitudes maximize at the equator, given an energetic proton ring-like distribution derived from an observed wave event, and using linear instability analysis and particle-in-cell simulations with the plasma conditions at different latitudes along the dipole magnetic field line. The results show that waves initially grow fastest (i.e., with the largest growth rate) at high latitude (20°-25°), but consistent with observations, their saturation amplitudes maximize within ±10° latitude. On the other hand, the slope of the saturation amplitudes versus latitude revealed in the present study is not as steep as what the previous statistical observation results suggest. This may be indicative of some other factors not considered in the present analyses at play, such as background magnetic field and plasma inhomogeneities and the propagation effect.
113
- Ayana, Selewondim Eshetu
- Journal of astronomy and space sciences
- 37, n.2
- pp.117-129
- 2020
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In a Satellite communication system, a link budget analysis is the detailed investigation of signal gains and losses moving through a channel from a sender to receiver. It inspects the fading of passed on data signal waves due to the process of spreading or propagation, including transmitter and receiver antenna gains, feeder cables, and related losses. The extent of the proposed tool is to make an effective, efficient, and user-friendly approach to calculate link budget analysis. It is also related to the satellite communication correlation framework by building up a graphical interface link analysis tool utilizing STK<sup>®</sup> software with the interface of C# programming. It provides better kinds of graphical display techniques, exporting and importing data files, printing link information, access data, azimuth-elevation-range (AER), and simulation is also possible at once. The components of the link budget analysis tool include transmitter gain, effective isotropic radiated power (EIRP), free space loss, propagation loss, frequency Doppler shift, flux density, link margin, elevation plot, etc. This tool can be useful for amateur users (e.g., CubeSat developers in the universities) or nanosat developers who may not know about the RF communication system of the satellite and the orbital mechanics (e.g., orbit propagators) principle used in the satellite link analysis.
114
- Park, Jeongchan
- Journal of astronomy and space sciences
- 37, n.1
- pp.61-68
- 2020
- 원문 바로보기
Recent studies have suggested that detectable ionospheric disturbances precede earthquakes. In the present study, variations in the vertical total electron content (TEC) for eight earthquakes with magnitudes of M ≥ 5.5 in the western United States were investigated during the solar maximum of 2013-2015 using United States total electron content (US-TEC) data provided by the National Oceanic and Atmospheric Administration. Analyses of 12 earthquakes with magnitudes of 5.0 ≤ M < 5.5 in the same region were also performed. The TEC variations were examined for 40 days, including the times when the earthquakes occurred. The results indicated a correlation between earthquakes with magnitudes of M ≥ 5.0 and ionospheric TEC anomalies. TEC anomalies occurred before 60% of the earthquakes. Additionally, they were more frequently observed for large earthquakes (75%, M ≥ 5.5) than for small earthquakes (50%, 5.5 > M ≥ 5.0). Anomalous increases in the TEC occurred 2-18 days before the earthquakes as an ionospheric precursor, whereas solar and geomagnetic activities were low or moderate.
115
- Jeong, Min-Ji
- Journal of astronomy and space sciences
- 36, n.2
- pp.75-86
- 2019
- 원문 바로보기
UV Psc is a typical RS CVn type system undergoing dynamic chromosphere activity. We performed photometric observations of the system in 2015 and secured new BVR light curves showing well-defined photometric waves. In this paper, we analyzed the light curves using Wilson-Devinney binary code and investigated the orbital period of the system. The combination of our light curve synthesis with the spectroscopic solution developed by previous investigators yielded the absolute parameters as: <TEX>$M_1=1.104{\pm}0.042M_{\odot}$</TEX>, <TEX>$R_1=1.165{\pm}0.025R_{\odot}$</TEX>, and <TEX>$L_1=1.361{\pm} 0.041L_{\odot}$</TEX> for the primary star, and <TEX>$M_2=0.809{\pm}0.082M_{\odot}$</TEX>, <TEX>$R_2=0.858{\pm}0.018R_{\odot}$</TEX>, and <TEX>$L_2=0.339 {\pm}0.010L_{\odot}$</TEX> for the secondary star. The eclipse timing diagram for accurate CCD and photoelectric timings showed that the orbital period may vary either in a downward parabolic manner or a quasi-sinusoidal pattern. If the latter is adopted as a probable pattern for the period change, a more plausible account for the cyclic variation may be the light time effect caused by a circumbinary object rather than an Applegate-mechanism occurring via variable surface magnetic field strengths.
116
- Hwang, Hyewon
- Journal of astronomy and space sciences
- 36, n.3
- pp.187-197
- 2019
- 원문 바로보기
The Optical Wide-field patroL-Network (OWL-Net) is a Korean optical space surveillance system used to track and monitor objects in space. In this study, the characteristics of four Initial Orbit Determination (IOD) methods were analyzed using artificial observational data from Low Earth Orbit satellites, and an appropriate IOD method was selected for use as the initial value of Precise Orbit Determination using OWL-Net data. Various simulations were performed according to the properties of observational data, such as noise level and observational time interval, to confirm the characteristics of the IOD methods. The IOD results produced via the OWL-Net observational data were then compared with Two Line Elements data to verify the accuracy of each IOD method. This paper, thus, suggests the best method for IOD, according to the properties of angles-only data, for use even when the ephemeris of a satellite is unknown.
117
- Kim, Simon
- Journal of astronomy and space sciences
- 36, n.2
- pp.97-103
- 2019
- 원문 바로보기
An automated signal-acquisition method for the NASA's space geodesy satellite laser ranging (SGSLR) system is described as a selection of two system parameters with specified probabilities. These parameters are the correlation parameter: the minimum received pulse number for a signal-acquisition and the frame time: the minimum time for the correlation parameter. The probabilities specified are the signal-detection and false-acquisition probabilities to distinguish signals from background noise. The steps of parameter selection are finding the minimum set of values by fitting a curve and performing a graph-domain approximation. However, this selection method is inefficient, not only because of repetition of the entire process if any performance values change, such as the signal and noise count rate, but also because this method is dependent upon system specifications and environmental conditions. Moreover, computation is complicated and graph-domain approximation can introduce inaccuracy. In this study, a new method is proposed to select the parameters via a conditional equation derived from characteristics of the signal-detection and false-acquisition probabilities. The results show that this method yields better efficiency and robustness against changing performance values with simplicity and accuracy and can be easily applied to other satellite laser ranging (SLR) systems.
118
- Kim, Dong-Heun
- Journal of astronomy and space sciences
- 36, n.4
- pp.283-292
- 2019
- 원문 바로보기
The purpose of this study was to develop a period analysis algorithm for detecting new variable stars in the time-series data observed by charge coupled device (CCD). We used the data from a variable star monitoring program of the CBNUO. The R filter data of some magnetic cataclysmic variables observed for more than 20 days were chosen to achieve good statistical results. World Coordinate System (WCS) Tools was used to correct the rotation of the observed images and assign the same IDs to the stars included in the analyzed areas. The developed algorithm was applied to the data of DO Dra, TT Ari, RXSJ1803, and MU Cam. In these fields, we found 13 variable stars, five of which were new variable stars not previously reported. Our period analysis algorithm were tested in the case of observation data mixed with various fields of view because the observations were carried with 2K CCD as well as 4K CCD at the CBNUO. Our results show that variable stars can be detected using our algorithm even with observational data for which the field of view has changed. Our algorithm is useful to detect new variable stars and analyze them based on existing time-series data. The developed algorithm can play an important role as a recycling technique for used data
119
- Na, Sung-Ho
- Journal of astronomy and space sciences
- 36, n.1
- pp.11-20
- 2019
- 원문 바로보기
Being a torque free motion of the rotating Earth, Chandler wobble is the major component in the Earth's polar motion with amplitude about 0.05-0.2 arcsec and period about 430-435 days. Free core nutation, also called nearly diurnal free wobble, exists due to the elliptical core-mantle boundary in the Earth and takes almost the whole part of un-modelled variation of the Earth's pole in the celestial sphere beside precession and nutation. We hereby present a brief summary of their theories and report their recent features acquired from updated datasets (EOP C04 and ECMWF) by using Fourier transform, modelling, and wavelet analysis. Our new findings include (1) period-instability of free core nutation between 420 and 450 days as well as its large amplitude-variation, (2) re-determined Chandler period and its quality factor, (3) fast decrease in Chandler amplitude after 2010.
120
- Shin, Youra
- Journal of astronomy and space sciences
- 36, n.1
- pp.1-9
- 2019
- 원문 바로보기
In this paper we present analysis of current density when the Cluster spacecraft pass the nightside auroral region at about <TEX>$4-5R_E$</TEX> from the center of Earth. The analysis is made when the inter-spacecraft separation is within 200 km, which allows all four spacecraft to be situated inside the same current sheet. On 22 February 2002, two field-aligned current (FAC) events were observed in both the southern and the northern hemispheres. The FACs were calculated with magnetic field data obtained by the four spacecraft using the Curlometer method. The scales of the FACs along the spacecraft trajectory and the magnitudes were hundreds of kilometers and tens of <TEX>$nA/m^2$</TEX>, respectively, and both events were mapped to the auroral region in the ionosphere. We also examined reliability of the results with some parameters, and found that our results are adequately comparable with other studies. Nevertheless, some limitations that decrease the accuracy of current estimation exist.