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- The Korean Space Science Society (The Korean Astronomical Society)
- 계간 (Quarterly)
- ISSN : 1225-052x (ISSN : 1225-052x)
1225-052x
- DB구축현황 : 1,253건 (DB Construction : 1,253 Articles)
총 게시글 1,253건
페이지 35/126
341
- Jee, Geonhwa
- Journal of astronomy and space sciences
- 31, n.2
- pp.169-176
- 2014
- 원문 바로보기
Since the operation of the King Sejong Station (KSS) started in Antarctic Peninsula in 1989, there have been continuous efforts to perform the observation for the upper atmosphere. The observations during the initial period of the station include Fabry-Perot Interferometer (FPI) and Michelson Interferometer for the mesosphere and thermosphere, which are no longer in operation. In 2002, in collaboration with York University, Canada, the Spectral Airglow Temperature Imager (SATI) was installed to observe the temperature in the mesosphere and lower thermosphere (MLT) region and it has still been producing the mesopause temperature data until present. The observation was extended by installing the meteor radar in 2007 to observe the neutral winds and temperature in the MLT region during the day and night in collaboration with Chungnam National University. We also installed the all sky camera in 2008 to observe the wave structures in the MLT region. All these observations are utilized to study on the physical characteristics of the MLT region and also on the wave phenomena such as the tide and gravity wave in the upper atmosphere over KSS that is well known for the strong gravity wave activity. In this article, brief introductions for the currently operating instruments at KSS will be presented with their applications for the study of the upper atmosphere.
342
- Lee, Jaewon
- Journal of astronomy and space sciences
- 31, n.1
- pp.33-39
- 2014
- 원문 바로보기
This paper describes an experimental approach to evaluate the effective doses of space radiations at high-altitude by combining the measured data from the Liulin-6K spectrometer loaded onto the air-borne RC-800 cockpit and the calculated data from CARI-6M code developed by FAA. In this paper, 15 exposed dose experiments for the flight missions at a high-altitude above 10 km and 3 experiments at a normal altitude below 4 km were executed over the Korean Peninsula in 2012. The results from the high-altitude flight measurements show a dramatic change in the exposed doses as the altitude increases. The effective dose levels (an average of <TEX>$15.27{\mu}Sv$</TEX>) of aircrew at the high-altitude are an order of magnitude larger than those (an average of <TEX>$0.30{\mu}Sv$</TEX>) of the normal altitude flight. The comparison was made between the measure dose levels and the calculated dose levels and those were similar each other. It indicates that the annual dose levels of the aircrew boarding RC-800 could be above 1 mSv. These results suggest that a proper procedure to manage the exposed dose of aircrew is required for ROK Air Force.
343
- Jeong, Meeyoung
- Journal of astronomy and space sciences
- 31, n.4
- pp.317-323
- 2014
- 원문 바로보기
Odyssey, one of the NASA's Mars exploration program and SELENE (Kaguya), a Japanese lunar orbiting spacecraft have a payload of Gamma-Ray Spectrometer (GRS) for analyzing radioactive chemical elements of the atmosphere and the surface. In these days, gamma-ray spectroscopy with a High-Purity Germanium (HPGe) detector has been widely used for the activity measurements of natural radionuclides contained in the soil of the Earth. The energy spectra obtained by the HPGe detectors have been generally analyzed by means of the Window Analysis (WA) method. In this method, activity concentrations are determined by using the net counts of energy window around individual peaks. Meanwhile, an alternative method, the so-called Full Spectrum Analysis (FSA) method uses count numbers not only from full-absorption peaks but from the contributions of Compton scattering due to gamma-rays. Consequently, while it takes a substantial time to obtain a statistically significant result in the WA method, the FSA method requires a much shorter time to reach the same level of the statistical significance. This study shows the validation results of FSA method. We have compared the concentration of radioactivity of <TEX>$^{40}K$</TEX>, <TEX>$^{232}Th$</TEX> and <TEX>$^{238}U$</TEX> in the soil measured by the WA method and the FSA method, respectively. The gamma-ray spectrum of reference materials (RGU and RGTh, KCl) and soil samples were measured by the 120% HPGe detector with cosmic muon veto detector. According to the comparison result of activity concentrations between the FSA and the WA, we could conclude that FSA method is validated against the WA method. This study implies that the FSA method can be used in a harsh measurement environment, such as the gamma-ray measurement in the Moon, in which the level of statistical significance is usually required in a much shorter data acquisition time than the WA method.
344
- Wu, Jason Hung Kit
- Journal of astronomy and space sciences
- 30, n.2
- pp.83-85
- 2013
- 원문 바로보기
Anomalous X-ray pulsars (AXPs) are thought to be magnetars which are young isolated neutron stars with extremely strong magnetic fields of > <TEX>$10^{14}$</TEX> Gauss. Their tremendous magnetic fields inferred from the spin parameters provide a huge energy reservoir to power the observed X-ray emission. High-energy emission above 0.3 MeV has never been detected despite intensive search. Here, we present the possible Fermi Large Area Telescope (LAT) detection of <TEX>${\gamma}$</TEX>-ray pulsations above 200 MeV from the AXP, 1E 2259+586, which puts the current theoretical models of <TEX>${\gamma}$</TEX>-ray emission mechanisms of magnetars into challenge. We speculate that the high-energy <TEX>${\gamma}$</TEX>-rays originate from the outer magnetosphere of the magnetar.
345
- Hui, Chung-Yue
- Journal of astronomy and space sciences
- 30, n.3
- pp.127-132
- 2013
- 원문 바로보기
Here we review the effort of Fermi Asian Network (FAN) in exploring the supernova remnants (SNRs) with state-of-art high energy observatories, including Fermi Gamma-ray Space Telescope and Chandra X-ray Observatory, in the period of 2011- 2012. Utilizing the data from Fermi LAT, we have discovered the GeV emission at the position of the Galactic SNR Kes 17 which provides evidence for the hadronic acceleration. Our study also sheds light on the propagation of cosmic rays from their acceleration site to the intersteller medium. We have also launched an identification campaign of SNR candidates in the Milky Way, in which a new SNR G308.3-1.4 have been uncovered with our Chandra observation. Apart from the remnant, we have also discovered an associated compact object at its center. The multiwavelength properties of this X-ray source suggest it can possibly be the compact binary that survived a supernova explosion.
346
- Oh, Suyeon
- Journal of astronomy and space sciences
- 30, n.3
- pp.175-178
- 2013
- 원문 바로보기
Recently, two instruments of cosmic ray are operating in South Korea. One is Seoul muon detector after October 1999 and the other is Daejeon neutron monitor (Kang et al. 2012) after October 2011. The former consists of four small plastic scintillators and the latter is the standard 18 NM 64 type. In this report, we introduce the characteristics of both instruments. We also analyze the flux variations of cosmic ray such as diurnal variation and Forbush decrease. As the result, the muon flux shows the typical seasonal and diurnal variations. The neutron flux also shows the diurnal variation. The phase which shows the maximum flux in the diurnal variation is around 13-14 local time. We found a Forbush decrease on 7 March 2012 by both instruments. It is also identified by Nagoya multi-direction muon telescope and Oulu neutron monitor. The observation of cosmic ray at Jangbogo station as well as in Korean peninsula can support the important information on space weather in local area. It can also enhance the status of Korea in the international community of cosmic ray experiments.
347
- Song, Young-Joo
- Journal of astronomy and space sciences
- 30, n.4
- pp.255-267
- 2013
- 원문 바로보기
In this research, the ground contact opportunity for the fictitious low lunar orbiter is analyzed to prepare for a future Korean lunar orbiter mission. The ground contact opportunity is basically derived from geometrical relations between the typical ground stations at the Earth, the relative positions of the Earth and Moon, and finally, the lunar orbiter itself. Both the cut-off angle and the orbiter's Line of Sight (LOS) conditions (weather orbiter is located at near or far side of the Moon seen from the Earth) are considered to determine the ground contact opportunities. Four KOMPSAT Ground Stations (KGSs) are assumed to be Korea's future Near Earth Networks (NENs) to support lunar missions, and world-wide separated Deep Space Networks (DSNs) are also included during the contact availability analysis. As a result, it is concluded that about 138 times of contact will be made between the orbiter and the Daejeon station during 27.3 days of prediction time span. If these contact times are converted into contact duration, the duration is found to be about 8.55 days, about 31.31% of 27.3 days. It is discovered that selected four KGSs cannot provide continuous tracking of the lunar orbiter, meaning that international collaboration is necessary to track Korea's future lunar orbiter effectively. Possible combinations of world-wide separated DSNs are also suggested to compensate for the lack of contact availability with only four KGSs, as with primary and backup station concepts. The provided algorithm can be easily modified to support any type of orbit around the Moon, and therefore, the presented results could aid further progress in the design field of Korea's lunar orbiter missions.
348
- Ko, Kyeongyeon
- Journal of astronomy and space sciences
- 30, n.4
- pp.307-314
- 2013
- 원문 바로보기
Infrared optical systems are operated at low temperature and vacuum (LT-V) condition, whereas the assembly and alignment are performed at room temperature and non-vacuum (RT-NV) condition. The differences in temperature and pressure between assembly/alignment environments and operation environment change the physical characteristics of optical and opto-mechanical parts (e.g., thickness, height, length, curvature, and refractive index), and the resultant optical performance changes accordingly. In this study, using input relay optics (IO), among the components of the Immersion GRating INfrared Spectrograph (IGRINS) which is an infrared spectrograph, a simulation based on the physical information of this optical system and an actual experiment were performed; and optical performances in the RT-NV, RT-V, and LT-V environments were predicted with an accuracy of <TEX>$0.014{\pm}0.007{\lambda}$</TEX> rms WFE, by developing an adaptive fitting line. The developed adaptive fitting line can quantitatively control assembly and alignment processes below <TEX>${\lambda}/70$</TEX> rms WFE. Therefore, it is expected that the subsequent processes of assembly, alignment, and performance analysis could not be repeated.
349
- Oh, Eunsong
- Journal of astronomy and space sciences
- 30, n.4
- pp.321-326
- 2013
- 원문 바로보기
The modulation transfer function (MTF) is a widely used indicator in assessments of remote-sensing image quality. This MTF method is also used to restore information to a standard value to compensate for image degradation caused by atmospheric or satellite jitter effects. In this study, we evaluated MTF values as an image quality indicator for the Geostationary Ocean Color Imager (GOCI). GOCI was launched in 2010 to monitor the ocean and coastal areas of the Korean peninsula. We evaluated in-orbit MTF value based on the GOCI image having a 500-m spatial resolution in the first time. The pulse method was selected to estimate a point spread function (PSF) with an optimal natural target such as a Seamangeum Seawall. Finally, image restoration was performed with a Wiener filter (WF) to calculate the PSF value required for the optimal regularization parameter. After application of the WF to the target image, MTF value is improved 35.06%, and the compensated image shows more sharpness comparing with the original image.
350
- Chung, Jiwon
- Journal of astronomy and space sciences
- 30, n.1
- pp.59-67
- 2013
- 원문 바로보기
We present a spectroscopic study of 343 blue compact galaxies (BCGs) at 0.20 < z < 0.35 from the Sloan Digital Sky Survey (SDSS) DR7 data. We derive gas phase oxygen abundance using the empirical and direct method. Stellar masses of galaxies are derived from the STARLIGHT code. We also derive star formation rates of galaxies based on <TEX>$H{\alpha}$</TEX> emission line from the SDSS as well as far-ultraviolet (FUV) flux from the Galaxy Evolution Explorer GR6 data. Evolution of the luminosity-metallicity and mass-metallicity (M-Z) relations with redshift is observed. At a given luminosity and mass, galaxies at higher redshifts appear to be biased to low metallicities relative to the lower redshift counterparts. Furthermore, low mass galaxies show higher specific star formation rates (SSFRs) than more massive ones and galaxies at higher redshifts are biased to higher SSFRs compared to the lower redshift sample. By visual inspection of the SDSS images, we classify galaxy morphology into disturbed or undisturbed. In the M-Z relation, we find a hint that morphologically disturbed BCGs appear to exhibit low metallicities and high SSFRs compared to undisturbed counterparts. We suggest that our results support downsizing galaxy formation scenario and star formation histories of BCGs are closely related with their morphologies.