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1968년 ~ 2023년까지 1,187 건의 한국천문학회지를 격월간 확인하실 수 있습니다.
- The Korean Astronomical Society (The Korean Astronomical Society)
- 계간 (Quarterly)
- ISSN : 1225-4614 (ISSN : 1225-4614)
1225-4614
- DB구축현황 : 1,187건 (DB Construction : 1,187 Articles)
총 게시글 1,187건
페이지 45/119
441
- Tadross, A.L.
- Journal of the Korean astronomical society = 천문학회지
- 38, n.3
- pp.357-363
- 2005
- 원문 바로보기
A deep stellar analysis is introduced for the poorly studied open cluster NGC 2509. The Near-IR database of the digital Two Micron All Sky Survey (2MASS) has been used to re-estimate and refine the fundamental parameters of the cluster, i.e. age, reddening, distance, and diameter. As well as, luminosity function, mass function, total mass, relaxation time, and mass segregation of NGC 2509 have been estimated here for the first time..
442
- NAKAJIMA YASUSHI
- Journal of the Korean astronomical society = 천문학회지
- 38, n.2
- pp.173-174
- 2005
- 원문 바로보기
On behalf of the IRSF/SIRIUS group, I introduce some recent results from our deep near-infrared surveys (J, Hand Ks bands, limiting magnitude of Ks=17) toward star forming regions in the Milky Way Galaxy (MWG) and Large Magellanic Cloud (LMC) with the near-infrared camera SIRIUS. We discovered a rich population of low-mass young stellar objects associated with the W3 and NGC 7538 regions in the MWG based on the near-infrared colors arid magnitudes. The high sensitivity of our survey enables us to detect intermediate-mass pre-main sequence stars, i.e. HAEBE stars, even in the LMC. We detected many HAEBE candidate stars in the N159/N160 complex star forming region in the LMC with the IRSF 1.4-m telescope. Spatial distributions of the young stellar objects indicate the sequential cluster formation in each star forming region in the complex and large scale (a few <TEX>${\times}$</TEX> 100 pc) sequential cluster formation over the entire complex.
443
- CHEN ALFRED BING-CHIH
- Journal of the Korean astronomical society = 천문학회지
- 38, n.2
- pp.303-306
- 2005
- 원문 바로보기
Transient luminous events (TLEs; sprites, elves, jets and etc.) are lightning-related optical flashes occurring above thunderstorms. Since the first discovery of sprites in 1989, scientists have learned a great deal about the morphological, spectroscopic and electromagnetic characteristics of TLEs through ground and spacecraft campaigns. However, most of the TLE studies were based on events recorded over US High Plains. To elucidate the possible biasing effects, space-borne observations are needed and have their merits. Imager of sprites and Upper Atmospheric Lightning (ISUAL) on the FORMOSAT-2 satellite is the first instrument to carry out a true global measurement of TLEs from a low- earth orbit. In this short paper, we apply a common astronomical data analysis technique, two-color diagram, on the ISUAL spectrophotometer (SP) data. By choosing appropriated bandpasses and converting the measured flux of TLEs into the unit of magnitude, two-color diagrams of TLEs can be constructed. We demonstrate that two-color diagrams, which were constructed from the narrow-band spectrophotometer data, can be used to classify different types of TLEs and trace their temporal evolution. The amount of reddening due to Earth's atmosphere can also be estimated from two-color diagrams assembled from the broad-band spectrophotometer data.
444
- OTA KAZUAKI
- Journal of the Korean astronomical society = 천문학회지
- 38, n.2
- pp.179-182
- 2005
- 원문 바로보기
We conducted an extremely wide field survey of z <TEX>${\~}$</TEX> 6 Lyman break galaxies (LBGs) to precisely derive their bright end surface density overcoming the bias due to cosmic variance. We selected out LBG candidates in the Subaru/ XMM-Newton Deep Survey Field (SXDS) over the total of <TEX>${\~}1.0\;deg^2$</TEX> sky area down to <TEX>$z_{AB} = 26.0 ({\ge}3{\sigma},\;2'.0 aperture)$</TEX> using i' - z' > 1.5 color cut. This sample alone is likely to be contaminated by M/L/T dwarfs, low-z elliptical galaxies, and z <TEX>${\~}$</TEX> 6 quasars. To eliminate these interlopers, we estimated their numbers using an exponential disk star count model, catalogs of old ellipticals in the SXDS and other field, and a z<TEX>${\~}$</TEX>6 quasar luminosity function. The finally derived surface density of z <TEX>${\~}$</TEX> 6 LBGs was 165 <TEX>$mag^{-1}\;deg^{-2}$</TEX> down to <TEX>$z_{AB}$</TEX> = 26.0 and shows good agreement with previous results from the narrower field survey of HST GOODS.
445
- KIM YONG HA
- Journal of the Korean astronomical society = 천문학회지
- 38, n.2
- pp.59-66
- 2005
- 원문 바로보기
A new ion transport code for planetary ionospheric studies has been developed with consideration of velocity differences among ion species involving ion-ion collision. Most of previous planetary ionosphere models assumed that ions diffuse through non-moving ion and neutral background in order to consolidate continuity and momentum equations for ions into a simple set of diffusion equations. The simplification may result in unreliable density profiles of ions at high altitudes where ion velocities are fast and their velocity differences are significant enough to cause inaccuracy when computing ion-ion collision. A new code solves explicitly one-dimensional continuity and momentum equations for ion densities and velocities by utilizing divided Jacobian matrices in matrix inversion necessary to the Newton iteration procedure. The code has been applied to Martian nightside ionosphere models, as an example computation. The computed density profiles of <TEX>$O^+,\;OH^+$</TEX>, and <TEX>$HCO^+$</TEX> differ by more than a factor of 2 at altitudes higher than 200 km from a simple diffusion model, whereas the density profile of the dominant ion, <TEX>$O_2^+$</TEX>, changes little. Especially, the density profile of <TEX>$HCO^+$</TEX> is reduced by a factor of about 10 and its peak altitude is lowered by about 40 km relative to a simple diffusion model in which <TEX>$HCO^+$</TEX> ions are assumed to diffuse through non-moving ion background, <TEX>$O_2^+$</TEX>. The computed effects of the new code on the Martian nightside models are explained readily in terms of ion velocities that were solved together with ion densities, which were not available from diffusion models. The new code should thus be expected as a significantly improved tool for planetary ionosphere modelling.
446
- SAKAI TAKESHI
- Journal of the Korean astronomical society = 천문학회지
- 38, n.2
- pp.257-260
- 2005
- 원문 바로보기
We have mapped the W 3 giant molecular cloud in the <TEX>$C^o\;^3P_1-^3 P_o$</TEX> ([CI]) line with the Mount Fuji Submillimeter-wave Telescope. The [CI] emission is extended over the molecular cloud, having peaks at three star forming clouds; W 3(Main), W 3(OH), and AFGL 333. The [CI] emission is found to be strong in the AFGL 333 cloud. We have also observed the <TEX>$C^{18}O,\;CCS,\;N_2H^+$</TEX>, and <TEX>$H^{13}CO^+$</TEX> lines by using the Nobeyama Radio Observatory 45 m telescope. In the AFGL 333 cloud, we find two massive cores, which are highly gravitationally bound and have no sign of active star formation. The high [<TEX>$C^o$</TEX>]/[CO] and [CCS]/[<TEX>$N_2H^+$</TEX>] abundance ratios suggest that the AFGL 333 cloud is younger than the W 3(Main) and W 3(OH) clouds.
447
- ICHIMOTO KIYOSHI
- Journal of the Korean astronomical society = 천문학회지
- 38, n.2
- pp.307-310
- 2005
- 원문 바로보기
The Solar-B is the third Japanese spacecraft dedicated for solar physics to be launched in summer of 2006. The spacecraft carries a coordinated set of optical, EUV and X-ray instruments that will allow a systematic study of the interaction between the Sun's magnetic field and its high temperature, ionized atmosphere. The Solar Optical Telescope (SOT) consists of a 50cm aperture diffraction limited Gregorian telescope and a focal plane package, and provides quantitative measurements of full vector magnetic fields at the photosphere with spatial resolution of 0.2-0.3 arcsec in a condition free from terrestrial atmospheric seeing. The X-ray telescope (XRT) images the high temperature (0.5 to 10 MK) corona with improved spatial resolution of approximately 1 arcsec. The Extreme Ultraviolet Imaging Spectrometer (EIS) aims to determine velocity fields and other plasma parameters in the corona and the transition region. The Solar-B telescopes, as a whole, will enable us to explore the origins of the outer solar atmosphere, the corona, and the coupling between the fine magnetic structure at the photosphere and the dynamic processes occurring in the corona. The mission instruments (SOT/EIS/XRT) are joint effort of Japan (JAXA/NAO), the United States (NASA), and the United Kingdom (PPARC). An overview of the spacecraft and its mission instruments are presented.
448
- KIM TAEHYUN
- Journal of the Korean astronomical society = 천문학회지
- 38, n.2
- pp.145-148
- 2005
- 원문 바로보기
We present a photometric study of galaxies in the central regions of six nearby galaxy clusters at redshift z=0.0231<TEX>${\~}$</TEX>0.0951. We have derived BVI photometry of the galaxies from the CCD images obtained at the Bohyunsan Optical Astronomical Observatory (BOAO) in Korea, and JHKs photometry of the bright galaxies from the 2MASS extended source catalog. Comparing the galaxy photometry results with the simple stellar population model of Bruzual & Charlot (2003) in the optical & NIR color-color diagrams, we have estimated the ages and metallicities of early type galaxies. We have found that the observed galaxies had recent star-formation mostly 5 <TEX>${\~}$</TEX> 7 Gyrs ago but the spread in age estimation is rather large. The average metallicities are [Fe/H]=0.l<TEX>${\~}$</TEX>0.5 dex. These results support the hypothesis that large early type galaxies in clusters are formed via hierarchical merging of smaller galaxies.
449
- ARDI ELIANI
- Journal of the Korean astronomical society = 천문학회지
- 38, n.2
- pp.207-210
- 2005
- 원문 바로보기
We study the influence of rotation on the dynamical evolution of collisional single-mass stellar clusters up to core-collapse by using N-body simulations. Rotating King models which are characterized by dimensionless central potential parameter <TEX>$W_o$</TEX> and the rotation parameter <TEX>$W_o$</TEX> are used as initial models. Our results show that inner shells slowly contract until core-collapse phase is reached, followed by a slow expansion. Angular momentum is transported outward, while the core is rotating even faster than before, as predicted by gravogyro catastrophe theory. We confirm that rotation plays an important role in accelerating the dynamical evolution of stellar cluster, in particular in accelerating the core collapse.
450
- ANN HONG BAE
- Journal of the Korean astronomical society = 천문학회지
- 38, n.2
- pp.121-124
- 2005
- 원문 바로보기
High resolution images of the nuclear regions of nearby galaxies show that nuclear spirals are preponderant in normal galaxies as well as in active galaxies. These nuclear spirals, especially the grand-design nuclear spirals are found to be formed by the gas flow driven by the bar. Hydrodynamical simulations exploring a wide range of parameter space show that the morphology of nuclear spirals depends not only on the inner dynamics but on the global dynamics resulting from the global mass distribution of galaxies. Thus, the nuclear morphology can be a diagnostic tool for the inner dynamics of galaxies when the global mass distribution is taken into account.