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1984년 ~ 2026년까지 1,258 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 : 1,258건 (DB Construction : 1,258 Articles)
총 게시글 1,258건
페이지 22/126
211
- Yushchenko, Alexander V.
- Journal of astronomy and space sciences
- 34, n.3
- pp.199-205
- 2017
- 원문 바로보기
A high resolution spectroscopic observation of the red supergiant star RM_1-390 in the Large Magellanic Cloud was made from a 3.6 m telescope at the European Southern Observatory. Spectral resolving power was R=20,000, with a signal-to-noise ratio S/N > 100. We found the atmospheric parameters of RM_1-390 to be as follows: the effective temperature <TEX>$T_{eff}=4,250{\pm}50K$</TEX>, the surface gravity <TEX>${\log}\;g=0.16{\pm}0.1$</TEX>, the microturbulent velocity <TEX>$v_</TEX><TEX>{micro}=2.5km/s$</TEX>, the macroturbulence velocity <TEX>$v_{macro}=9km/s$</TEX> and the iron abundance <TEX>$[Fe/H</TEX><TEX>]</TEX><TEX>=-0.73{\pm}0.11$</TEX>. The abundances of 18 chemical elements from silicon to thorium in the atmosphere of RM_1-390 were found using the spectrum synthesis method. The relative deficiencies of all elements are close to that of iron. The fit of abundance pattern by the solar system distribution of r- and s-element isotopes shows the importance of the s-process. The plot of relative abundances as a function of second ionization potentials of corresponding chemical elements allows us to find a possibility of convective energy transport in the photosphere of RM_1-390.
212
Chemical Composition of RR Lyn - an Eclipsing Binary System with Am and λ Boo Type Components
- Jeong, Yeuncheol
- Journal of astronomy and space sciences
- 34, n.2
- pp.75-82
- 2017
- 원문 바로보기
High-resolution spectroscopic observations of the eclipsing binary system RR Lyn were made using the 1.8 m telescope at the Bohuynsan Optical Astronomical Observatory in Korea. The spectral resolving power was R = 82,000, with a signal to noise ratio of S/N > 150. We found the effective temperatures and surface gravities of the primary and secondary components to be equal to <TEX>$T_{eff}$</TEX> = 7,920 & 7,210 K and log(g) = 3.80 & 4.16, respectively. The abundances of 34 and 17 different chemical elements were found in the atmospheric components. Correlations between the derived abundances with condensation temperatures and the second ionization potentials of these elements are discussed. The primary component is a typical metallic line star with the abundances of light and iron group elements close to solar values, while elements with atomic numbers Z > 30 are overabundant by 0.5-1.5 dex with respect to solar values. The secondary component is a <TEX>${\lambda}$</TEX> Boo type star. In this type of stars, CNO abundances are close to solar values, while the abundance pattern shows a negative correlation with condensation temperatures.
213
- Moon, Byeongha
- Journal of astronomy and space sciences
- 34, n.2
- pp.99-103
- 2017
- 원문 바로보기
The sun is not equally bright over the whole sphere, but rather is darkened toward the limb. This effect is well-known as limb darkening. The limb darkening coefficient is defined by the ratio of the center intensity to limb intensity. In this study, we calculate the limb darkening coefficient using the photospheric intensity estimated from solar images taken by solar and helispheric observatory (SOHO) and solar dynamics observatory (SDO). The photospheric intensity data cover almost two solar cycles from May 1996 to December 2016. The limb darkening coefficient for a size of 0.9 diameter is about 0.69 and this value is consistent with solar limb darkening. The limb darkening coefficient estimated from SOHO shows a temporal increase at solar maximum and a gradual increase since the solar minimum of 2008. The limb darkening coefficient estimated from SDO shows a constant value of about 0.65 and a decreasing trend since 2014. The increase in the coefficient reflects the effect of weakened solar activity. However, the decrease since 2014 is caused by the aging effect.
214
- Han, Mihwa
- Journal of astronomy and space sciences
- 34, n.2
- pp.83-97
- 2017
- 원문 바로보기
We present extra-tidal features of spatial configuration of stars around three metal-poor globular clusters (NGC 6266, NGC 6273, NGC 6681) located in the Galactic bulge. The wide-field photometric data were obtained in BVI bands with the MOSAIC II camera at CTIO 4 m Blanco telescope. The derived color-magnitude diagrams (CMDs) contain stars in a total <TEX>$71^{\prime}{\times}71^{\prime}$</TEX> area including a cluster and its surrounding field outside of the tidal radius of the cluster. Applying statistical filtering technique, we minimized the field star contaminations on the obtained cluster CMDs and extracted the cluster members. On the spatial stellar density maps around the target clusters, we found overdensity features beyond the tidal radii of the clusters. We also found that the radial density profiles of the clusters show departures from the best-fit King model for their outer regions which support the overdensity patterns.
215
- Ryu, Kwangsun
- Journal of astronomy and space sciences
- 34, n.4
- pp.343-352
- 2017
- 원문 바로보기
A space plasma facility has been operated with a back-diffusion-type plasma source installed in a mid-sized vacuum chamber with a diameter of ~1.5 m located in Satellite Technology Research Center (SaTReC), Korea Advanced Institute of Science and Technology (KAIST). To generate plasma with a temperature and density similar to the ionospheric plasma, nickel wires coated with carbonate solution were used as filaments that emit thermal electrons, and the accelerated thermal electrons emitted from the heated wires collide with the neutral gas to form plasma inside the chamber. By using a disk-type Langmuir probe installed inside the vacuum chamber, the generation of plasma similar to the space environment was validated. The characteristics of the plasma according to the grid and plate anode voltages were investigated. The grid voltage of the plasma source is realized as a suitable parameter for manipulating the electron density, while the plate voltage is suitable for adjusting the electron temperature. A simple physical model based on the collision cross-section of electron impact on nitrogen molecule was established to explain the plasma generation mechanism.
216
- Choi, Eun-Jung
- Journal of astronomy and space sciences
- 34, n.4
- pp.303-314
- 2017
- 원문 바로보기
With increased human activity in space, the risk of re-entry and collision between space objects is constantly increasing. Hence, the need for space situational awareness (SSA) programs has been acknowledged by many experienced space agencies. Optical and radar sensors, which enable the surveillance and tracking of space objects, are the most important technical components of SSA systems. In particular, combinations of radar systems and optical sensor networks play an outstanding role in SSA programs. At present, Korea operates the optical wide field patrol network (OWL-Net), the only optical system for tracking space objects. However, due to their dependence on weather conditions and observation time, it is not reasonable to use optical systems alone for SSA initiatives, as they have limited operational availability. Therefore, the strategies for developing radar systems should be considered for an efficient SSA system using currently available technology. The purpose of this paper is to analyze the performance of a radar system in detecting and tracking space objects. With the radar system investigated, the minimum sensitivity is defined as detection of a <TEX>$1-m^2$</TEX> radar cross section (RCS) at an altitude of 2,000 km, with operating frequencies in the L, S, C, X or Ku-band. The results of power budget analysis showed that the maximum detection range of 2,000 km, which includes the low earth orbit (LEO) environment, can be achieved with a transmission power of 900 kW, transmit and receive antenna gains of 40 dB and 43 dB, respectively, a pulse width of 2 ms, and a signal processing gain of 13.3 dB, at a frequency of 1.3 GHz. We defined the key parameters of the radar following a performance analysis of the system. This research can thus provide guidelines for the conceptual design of radar systems for national SSA initiatives.
217
- Yeom, Bum-Suk
- Journal of astronomy and space sciences
- 34, n.3
- pp.183-197
- 2017
- 원문 바로보기
We present simulations of the optical-band images of high-redshift galaxies utilizing 845 near-ultraviolet (NUV) images of nearby galaxies obtained through the Galaxy Evolution Explorer (GALEX). We compute the concentration (C), asymmetry (A), Gini (G), and <TEX>$M_{20}$</TEX> parameters of the GALEX NUV/Sloan Digital Sky Survey r-band images at z ~ 0 and their artificially redshifted optical images at z = 0.9 and 1.6 in order to quantify the morphology of galaxies at local and high redshifts. The morphological properties of nearby galaxies in the NUV are presented using a combination of morphological parameters, in which early-type galaxies are well separated from late-type galaxies in the <TEX>$G-M_{20}$</TEX>, <TEX>$C-M_{20}$</TEX>, A-C, and <TEX>$A-M_{20}$</TEX> planes. Based on the distribution of galaxies in the A-C and <TEX>$G-M_{20}$</TEX> planes, we examine the morphological K-correction (i.e., cosmological distance effect and bandshift effect). The cosmological distance effect on the quantitative morphological parameters is found to be significant for early-type galaxies, while late-type galaxies are more greatly affected by the bandshift effect. Knowledge of the morphological K-correction will set the foundation for forthcoming studies on understanding the quantitative assessment of galaxy evolution.
218
- Jung, Jongil
- Journal of astronomy and space sciences
- 33, n.4
- pp.345-348
- 2016
- 원문 바로보기
In December 2015, we have installed neutron monitor at the Jang Bogo station in Antarctica. The Jang Bogo station is the second science station which is located at the coast (<TEX>$74^{\circ}\;37.4^{\prime}S$</TEX>, <TEX>$164^{\circ}\;13.7^{\prime}E$</TEX>) of Terra Nova Bay in Northern Victoria Land of Antarctica. A neutron monitor is an instrument to detect neutrons from secondary cosmic rays collided by the atmosphere. The installation of neutron monitor at Jang Bogo station is a part of transferred mission for neutron monitor at McMurdo station of USA. Among 18 tubes of 18-NM64 neutron monitor, we have completed relocation of 6 tubes and the rest will be transferred in December 2017. Currently, comparison of data from both neutron monitors is under way and there is a good agreement between the data. The neutron monitor at Jang Bogo station will be quite useful to study the space weather when the installation is completed.
219
- Kim, Sang Hyuk
- Journal of astronomy and space sciences
- 33, n.1
- pp.55-62
- 2016
- 원문 바로보기
Heumgyeonggaknu (欽敬閣漏) is powered by a water-hammering-type water wheel. The technique that maintains the constant speed of the water wheel is assumed to be the one used in the Cheonhyeong (天衡) apparatus in Shui Yun Yi Xiang Tai (水運儀象臺) made by the Northern Song (北宋) dynasty in the 11<sup>th</sup> century. We investigated the history of the development and characteristics of the Cheonhyeong apparatus, and we analyzed ways to transmit the power of Heumgyeonggaknu. In addition, we carried out a conceptual design to systematically examine the power control system. Based on the conceptual design, we built a model for a water wheel control system that could be used in experiments by drawing a 3D model and a basic design.
220
- Admiranto, Agustinus G.
- Journal of astronomy and space sciences
- 33, n.3
- pp.197-205
- 2016
- 원문 바로보기
We investigated two flares in the solar atmosphere that occurred on June 3, 2012 and July 6, 2012 and caused propagation of Moreton and EIT waves. In the June 3 event, we noticed a filament winking which presumably was caused by the wave propagation from the flare. An interesting feature of this event is that there was a reflection of this wave by a coronal hole located alongside the wave propagation, but not all of this wave was transmitted by the coronal hole. Using the running difference method, we calculated the speed of Moreton and EIT waves and we found values of 926 km/s before the reflection and 276 km/s after the reflection (Moreton wave) and 1,127 km/s before the reflection and 46 km/s after the reflection (EIT wave). In the July 6 event, this phenomenon was accompanied by type II and type III solar radio bursts, and we also performed a running difference analysis to find the speed of the Moreton wave, obtaining a value of 988 km/s. The speed derived from the analysis of the solar radio burst was 1,200 km/s, and we assume that this difference was caused by the different nature of the motions in these phenomena, where the solar radio burst was caused by the propagating particles, not waves.