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1968년 ~ 2024년까지 1,211 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 : 1,211건 (DB Construction : 1,211 Articles)
총 게시글 1,211건
페이지 67/122
661
- YUN HONG SIK
- Journal of the Korean astronomical society = 천문학회지
- 36, n.suppl1
- pp.155-161
- 2003
- 원문 바로보기
In this article I review the past and current status of solar astronomy in Korea and present some future prospects. Along with a brief historical account on the introduction of modern astronomy to Korea, I describe in detail how solar astronomy in Korea has developed since its birth about 20 years ago. With education of solar astronomers at domestic universities and collaboration with foreign scientists in China, Japan and the U. S., there has been a rapid growth of solar physics in Korea in the past decade. For further advance of solar astronomy in Korea, Korean solar astronomers have to build their own observing facilities and develop instrumentation programs. Also it is very important to bring up manpower competent for these projects.
662
- CHAE JONGCHUL
- Journal of the Korean astronomical society = 천문학회지
- 35, n.1
- pp.59-65
- 2002
- 원문 바로보기
Solar observations support that magnetic reconnect ion ubiquitously occurs in the chromosphere as well as in the corona. It is now widely accepted that coronal magnetic reconnect ion is fast reconnect ion of the Petschek type, and is the main driver of solar flares. On the other hand, it has been thought that the traditional Sweet-Parker model may describe chromospheric reconnect ion without difficulty, since the electric conductivity in the chromoshphere is much lower than that in the corona. However, recent observations of cancelling magnetic features have suggested that chromospheric reconnect ion might proceed at a faster rate than the Sweet-Parker model predicts. We have applied the Sweet-Parker model and Petschek model to a well-observed cancelling magnetic feature. As a result, we found that the inflow speed of the Sweet-Parker reconnect ion is too small to explain the observed converging speed of the feature. On the other hand, the inflow speeds and outflow speeds of the Petschek reconnect ion are well compatible with observations. Moreover, we found that the Sweet-Parker type current sheet is subject to the ion-acoustic instability in the chromosphere, implying the Petschek mechanism may operate there. Our results strongly suggest that chromospheric reconnect ion is of the Petschek type.
663
- YANG YUJIN
- Journal of the Korean astronomical society = 천문학회지
- 35, n.3
- pp.131-141
- 2002
- 원문 바로보기
We present Near-IR photometry of the Arches cluster, a young and massive stellar cluster near the Galactic center. We have analyzed the high resolution (FWHM <TEX>$\~$</TEX> 0.2') Hand K' band images in the Galactic Center Demonstration Science Data Set, which were obtained with the Gemini/Hokupa's adaptive optics (AO) system. We present the color-magnitude diagram, the luminosity function and the initial mass function (IMF) of the stars in the Arches cluster in comparison with the HST/NICMOS data. The IMF slope for the range of 1.0 < log (M/M<TEX>$\bigodot$</TEX>) < 2.1 is estimated to be <TEX>${\Gamma} = -0.79 {\pm} 0.16$</TEX>, in good agreements with the earlier result based on the HST/NICMOS data [Figer et al. 1999, ApJ, 525, 750]. These results strengthen the evidence that the IMF of the bright. stars close to the Galactic center is much flatter than that for the solar neighborhood. This is also consistent with a recent finding that the IMFs of the bright stars in young clusters in M33 get flatter as the galactocentric distance decreases [Lee et al. 2001, astro-ph 0109258]. It is found that the power of the Gemini/ AO system is comparable, with some limits, to that of the HST/NICMOS.
664
- HONG S. S.
- Journal of the Korean astronomical society = 천문학회지
- 35, n.1
- pp.41-57
- 2002
- 원문 바로보기
We have written a code called QDM_sca, which numerically solves the problem of radiative transfer in an anisotropically scattering, spherical atmosphere. First we formulate the problem as a second order differential equation of a quasi-diffusion type. We then apply a three-point finite differencing to the resulting differential equation and transform it to a tri-diagonal system of simultaneous linear equations. After boundary conditions are implemented in the tri-diagonal system, the QDM_sca radiative code fixes the field of specific intensity at every point in the atmosphere. As an application example, we used the code to calculate the brightness of atmospheric diffuse light(ADL) as a function of zenith distance, which plays a pivotal role in reducing the zodiacal light brightness from night sky observations. On the basis of this ADL calculation, frequent uses of effective extinction optical depth have been fully justified in correcting the atmospheric extinction for such extended sources as zodiacal light, integrated starlight and diffuse galactic light. The code will be available on request.
665
- LEE YOUNGUNG
- Journal of the Korean astronomical society = 천문학회지
- 35, n.2
- pp.97-103
- 2002
- 원문 바로보기
We have mapped 1 <TEX>$deg^2$</TEX> region toward a high latitude cloud MBM 40 in the J = 1 - 0 transition of <TEX>$^{12}CO$</TEX> and <TEX>$^{13}CO$</TEX>, using the 3 mm SIS receiver on the 14 m telescope at Taeduk Radio Astronomy Observatory. We used a high resolution autocorrelator to resolve extremely narrow CO linewidths of the molecular gas. Though the linewidth of the molecular gas is very narrow (FWHP < 1 km <TEX>$s^{-1}$</TEX> ), it is found that there is an evident velocity difference between the middle upper part and the lower part of the cloud. Their spectra for both of <TEX>$^{12}CO$</TEX> and <TEX>$^{13}CO$</TEX> show blue wings, and the position-velocity map shows clear velocity difference of 0.4 km <TEX>$s^{-1}$</TEX> between two parts. The mean velocity of the cloud is 3.1 km <TEX>$s^{-1}$</TEX>. It is also found that the linewidths at the blueshifted region are broader than those of the rest of the cloud. We confirmed that the visual extinction is less than 3 magnitude, and the molecular gas is translucent. We discussed three mass estimates, and took a mass of 17 solar masses from CO integrated intensity using a conversion factor <TEX>$2.3 {\times} 10^{20} cm^{-2} (K\;km s^{-1})^{-1}$</TEX>. Spatial coincidence and close morphological similarity is found between the CO emission and dust far-infrared (FIR) emission. The ratio between the 100 f.Lm intensity and CO integrated intensity of MBM 40 is 0.7 (MJy/sr)/(K km <TEX>$s^{-1}$</TEX>), which is larger than those of dark clouds, but much smaller than those of GMCs. The low ratio found for MBM 40 probably results from the absence of internal heating sources, or significant nearby external heating sources.
666
- YIM KI-JEONG
- Journal of the Korean astronomical society = 천문학회지
- 35, n.2
- pp.75-85
- 2002
- 원문 바로보기
We present N-body simulations of globular clusters including gravitational field of the Galaxy, in order to study effects of tidal field systematically on the shape of outer parts of globular clusters using NBODY6. The Galaxy is assumed to be composed of central bulge and outer halo. We mvestigate the cluster of multi-mass models with a power-law initial mass function (IMF) starting with different initial masses, initial number of particles, different slopes of the IMF and different orbits of the cluster. We have examined the general evolution of the clusters, the shape of outer parts of the clusters, density profiles and the direction of tidal tails. The density profiles appear to become somewhat shallower just outside the tidal boundary consistent with some observed data. The position angle of the tidal tall depends on the location in the Galaxy as well as the direction of the motion of. clusters. We found that the clusters become more elongated at the apogalacticon than at the pengalacticon. The tidal tails may be used to trace the orbital paths of globular clusters.
667
- KANG HYESUNG
- Journal of the Korean astronomical society = 천문학회지
- 35, n.4
- pp.159-174
- 2002
- 원문 바로보기
Cosmological hydrodynamic simulations of large scale structure in the universe have shown that accretion shocks and merger shocks form due to flow motions associated with the gravitational collapse of nonlinear structures. Estimated speed and curvature radius of these shocks could be as large as a few 1000 km/s and several Mpc, respectively. According to the diffusive shock acceleration theory, populations of cosmic-ray particles can be injected and accelerated to very high energy by astrophysical shocks in tenuous plasmas. In order to explore the cosmic ray acceleration at the cosmic shocks, we have performed nonlinear numerical simulations of cosmic ray (CR) modified shocks with the newly developed CRASH (Cosmic Ray Amr SHock) numerical code. We adopted the Bohm diffusion model for CRs, based on the hypothesis that strong Alfven waves are self-generated by streaming CRs. The shock formation simulation includes a plasma-physics-based 'injection' model that transfers a small proportion of the thermal proton flux through the shock into low energy CRs for acceleration there. We found that, for strong accretion shocks, CRs can absorb most of shock kinetic energy and the accretion shock speed is reduced up to <TEX>$20\%$</TEX>, compared to pure gas dynamic shocks. For merger shocks with small Mach numbers, however, the energy transfer to CRs is only about <TEX>$10-20\%$</TEX> with an associated CR particle fraction of <TEX>$10^{-3}$</TEX>. Nonlinear feedback due to the CR pressure is insignificant in the latter shocks. Although detailed results depend on models for the particle diffusion and injection, these calculations show that cosmic shocks in large scale structure could provide acceleration sites of extragalactic cosmic rays of the highest energy.
668
- KANG YaNG-WOO
- Journal of the Korean astronomical society = 천문학회지
- 35, n.2
- pp.87-95
- 2002
- 원문 바로보기
We have conducted VI CCD photometry of the open cluster NGC 6819 in order to understand the effects of dynamical evolution in old open clusters. Our photometry covers 18' <TEX>$\times$</TEX> 18' on the sky, centered on the cluster, which seems to cover the whole cluster field. Our photometry reaches down to V <TEX>$\approx$</TEX> 20.5, which allows us to analyze the luminosity function and spatial distribution of stars brighter than Mv <TEX>$\approx$</TEX> 8.5. There is a clear evidence for mass segregation in NGC 6819, i.e., the giants and upper main-sequence stars are concentrated in the inner regions, whereas the lower main-sequence stars distribute almost uniformly throughout the cluster. The luminosity function of the main-sequence stars of NGC 6819 is almost flat. The flat luminosity function indicates that a large number of low mass stars has escaped from the cluster unless its initial mass function is much different from the Salpeter type (<TEX>${\phi}(m){\propto} m^{-(1+x)},x = 1.35$</TEX>).
669
- MOON Y.-J.
- Journal of the Korean astronomical society = 천문학회지
- 35, n.3
- pp.143-149
- 2002
- 원문 바로보기
In this paper we present a methodology to derive the temporal change of the magnetic shear angle from a series of vector magnetograms, with a high time cadence. This method looks for the minimum change of the shear angle between a pair of magnetograms, free from the <TEX>$180^{\circ}$</TEX> ambiguity, and then accumulates this change over many successive pairs to derive the temporal change of magnetic shear. This methodology will work well if only the successive magnetograms occurred in an active region are well aligned and its helicity sign is reasonably determined. We have applied this methodology to a set of vector magnetograms of NOAA Active Region 9661 on October 19, 2001 by the new digital magnetograph at the Big Bear Solar Observatory (BBSO). For this work we considered well aligned magnetograms whose cross-correlation values are larger than 0.95. As a result, we have confirmed the recent report of Wang et al. that there was the abrupt shear change associated with the X1.6 flare. It is also demonstrated that the shear change map can be an useful tool to highlight the local areas that experienced the abrupt shear change. Finally, we suggest that this observation should be a direct support of the emergence of sheared magnetic fields.
670
- YUSHCHENKO ALEXANDER
- Journal of the Korean astronomical society = 천문학회지
- 35, n.4
- pp.209-220
- 2002
- 원문 바로보기
In order to increase the completeness of the investigations of stellar abundances, we can use spectrum synthesis method, new atomic data and observation of stellar spectra with resolution comparable to solar spectral atlases. We made a brief review of main problems of these three ways. We present new results of abundance determinations in the atmospheres of four stars. The first is the implementation of new atomic data to well known Przybylski's star. We show that the number of spectral lines, which can be identificated in the spectrum of this star, can be significantly higher. The second example is the investigation of <TEX>$\zeta$</TEX> Cyg. We found the abundances of 51 elements in the atmosphere of this mild barium star. The third example is halo star HD221170. Our preliminary abundance pattern consists of 42 elements. The heaviest elements in this pattern are U and Th. The last star is the spectroscopic binary HD153720. The number of elements investigated in the spectra of components of this star is not large, but the results show that the components are Am-stars.