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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 75/122
741
- LEE HVUNSOOK
- Journal of the Korean astronomical society = 천문학회지
- 33, n.1
- pp.57-73
- 2000
- 원문 바로보기
We have done a spectroscopic study of the solar transition region using high resolution UV & EUV data obtained by SUMER(Solar Ultraviolet Measurements of Emitted Radiation) on board SOHO(Solar and Heliospheric Observatory). Optically thin and conspicuous emission lines observed at the solar limb are carefully selected to acquire average values of physical parameters for the quiet region as a function of radial distance. Our main results found from the present study can be summarized as follows. 1) Nonthermal velocities estimated from various UV lines do not decrease with height at least within one total line intensity scale height above the limb. 2) Nonthermal velocity distribution with temperature is very similar to that of the disk center, in the sense that its peak is located around <TEX>$2{\times}10^5 K$</TEX>, but the value is systematically larger than that of the disk. 3) It is found that nonthermal velocity is inversely proportional. to quadratic root of electron density up to about 10 arc seconds above the limb, i.e. <TEX>${\xi}\~N_e^{-1/4}$</TEX>, implying that the observed nonthermal broadening can be attributed to Alfven waves passing through the medium. 41 Electron density estimated from the O V 629/760 line ratio is found to range from about <TEX>$1{\times}10^{10}cm^{-3}$</TEX> to <TEX>$2{\times} 10^{12}cm^{-3}$</TEX> in the transition region.
742
- 안영숙
- Journal of the Korean astronomical society = 천문학회지
- 33, n.3
- pp.177-183
- 2000
- 원문 바로보기
We arrange Korean ancient calendar with Solar calendar during Choseon Dynasty(A.D. 1392-1910). In this period, we have one representable history books and several books, and most of information for date are found from them, ChoseonWangjosillok(조선왕조실록) and Jeungbomunheonbigo(증보문헌비고), etc. In those books many astronomical data and calendar information data are contained, so we can make chronological tables. Most of the data are arranged based on those several books, and for doubtable data are identified from eclipse, historical events and lunar phase calculations etc. We find that arranged chronological tables during Choseon Dynasty are similar to that of China and somewhat different from that of Japan. In addition we summarize all misrecorded date data in ChoseonWangjosillok
743
- ANN HONG BAE
- Journal of the Korean astronomical society = 천문학회지
- 33, n.1
- pp.1-17
- 2000
- 원문 바로보기
We have performed extensive simulations of response of gaseous disk in barred galaxies using SPH method. The gravitational potential is assumed to be generated by disk, bulge, halo, and bar. The mass of gaseous disk in SPH simulation is assumed to be negligible compared to the stellar and dark mass component, and the gravitational potential generated by other components is fixed in time. The self-gravity of the gas is not considered in most simulations, but we have made a small set of simulations including the self-gravity of the gas. Non-circular component of velocity generated by the rotating, non-axisymmetric potential causes many interesting features. In most cases, there is a strong tendency of concentration of gas toward the central parts of the galaxy. The morphology of the gas becomes quite complex, but the general behavior can be understood in terms of simple linear approximations: the locations and number of Lindblad resonances play critical role in determining the general distribution of the gas. We present our results in the form of 'atlas' of artificial galaxies. We also make a brief comment on the observational implications of our calculations. Since the gaseous component show interesting features while the stellar component behaves more smoothly, high resolution mapping using molecular emission line for barred galaxies would be desirable.
744
- KIM YONG HA
- Journal of the Korean astronomical society = 천문학회지
- 33, n.2
- pp.127-135
- 2000
- 원문 바로보기
We investigate the effects of planetary rotation on the exospheres of the earth and Mars with simple collisionless models. We develope a numerical code that computes exospheric densities by integrating velocity functions at the exobase with a 10 point Gauss method. It is assumed in the model that atoms above the exobase altitude move collisionlessly on an orbit under the planet's gravity. Temperatures and densities at the exobase over the globe are adopted from MSIS-86 for the earth and from Bougher et al's MTGCM for Mars. For both the earth and Mars, the rotation affects the exospheric density distribution significantly in two ways: (1) the variation of the exospheric density distribution is shifted toward the rotational direction with respect to the variation at the exobase, (2) the exospheric densities in general increase over the non-rotating case. We find that the rotational effects are more significant for lower thermospheric temperatures. Both the enhancement of densities and shift of the exospheric distribution due to rotation have not been considered in previous models of Martian exosphere. Our non-spherical distribution with the rotational effects should contribute to refining the hot oxygen corona models of Mars which so far assume simple geometry. Our model will also help in analyzing exospheric data to be measured by the upcoming Nozomi mission to Mars.
745
- 유계화
- Journal of the Korean astronomical society = 천문학회지
- 33, n.3
- pp.173-175
- 2000
- 원문 바로보기
The time-dependence of an <TEX>$\alpha$</TEX>-disk model under the influence of collisions of particles is examined. Collisions with viscosity tend to take away angular momentum. Both effects cause the disk to rotate more rapidly. The disk gradually contracts with increasing time.
746
- MOON Y.-J.
- Journal of the Korean astronomical society = 천문학회지
- 33, n.1
- pp.47-55
- 2000
- 원문 바로보기
Nonpotential characteristics of magnetic fields in AR 5747 are examined using Mees Solar Observatory magnetograms taken on Oct. 20, 1989 to Oct. 22, 1989. The active region showed such violent flaring activities during the observational span that strong X-ray flares took place including a 2B/X3 flare. The magnetogram data were obtained by the Haleakala Stokes Polarimeter which provides simultaneous Stokes profiles of the Fe I doublet 6301.5 and 6302.5. A nonlinear least square method was adopted to derive the magnetic field vectors from the observed Stokes profiles and a multi-step ambiguity solution method was employed to resolve the <TEX>$180^{\circ}$</TEX> ambiguity. From the ambiguity-resolved vector magnetograms, we have derived a set of physical quantities characterizing the field configuration, which are magnetic flux, vertical current density, magnetic shear angle, angular shear, magnetic free energy density, a measure of magnetic field discontinuity MAD and linear force-free coefficient. Our results show that (1) magnetic nonpotentiality is concentrated near the inversion line in the flaring sites, (2) all the physical parameters decreased with time, which may imply that the active region was in a relaxation stage of its evolution, (3) 2-D MAD has similar patterns with other nonpotential parameters, demonstrating that it can be utilized as an useful parameter of flare producing active region, and (4) the linear force-free coefficient could be a evolutionary indicator with a merit as a global nonpotential parameter.
747
- KYEONG JAE-MANN
- Journal of the Korean astronomical society = 천문학회지
- 33, n.3
- pp.143-149
- 2000
- 원문 바로보기
We present the results of near-IR band (JHK) photometric study for the old open cluster To 2. Combined with existing optical data, our IR photometry is used to derive the reddening E(B- V)=0.24<TEX>$\pm$</TEX>0.12 and the distance (m-M)o=14.6<TEX>$\pm$</TEX>0.42. Comparison with theoretical isochrones suggests the age and metallicity of To 2 are log t<TEX>$\~$</TEX>9.3 and [Fe/H]<TEX>$\~$</TEX>-0.3, respectively.
748
- KIM HYUN-GOO
- Journal of the Korean astronomical society = 천문학회지
- 33, n.3
- pp.151-158
- 2000
- 원문 바로보기
We conducted a deep CCD observations in V band to obtain stellar density distribution and to determine the distances toward two molecular clouds with anomalous velocity in the Galactic anti-center region. Star count method based on the linear programming technique was applied to the CCD photometric data. We found two prominent peaks at distances of around 1.4 and 2.7 kpc. It is found that the first peak coincides well with stellar density enhancement of B8-A0 stars and the second one with the outer Perseus arm. The effect of the choice of the luminosity function is discussed. The stellar number density distribution is used to derive the distances to the molecular clouds and the visual extinctions caused by the clouds. We found that two molecular clouds are located almost at the same distance of about 1.1 <TEX>$\pm$</TEX> 0.1 kpc, and the peak extinctions caused by the clouds are about 2.2 <TEX>$\pm$</TEX> 0.3 mag in V band.
749
- AHN SANG-HYEON
- Journal of the Korean astronomical society = 천문학회지
- 33, n.1
- pp.29-36
- 2000
- 원문 바로보기
We developed a Monte Carlo code that describes the resonant Ly<TEX>$\alpha$</TEX> line transfer in an optically thick, dusty, and static medium. The code was tested against the analytic solution derived by Neufeld (1990). We explain the line transfer mechanism by tracing histories of photons in the medium. We find that photons experiences a series of wing scatterings at the moment of thier escape from the medium, during which polarization may develop. We examined the amount of dust extinction for a wide range of dust abundances, which are compared with the analytic solution. Brief discussions on the astrophysical application of our work are presented.
750
- LEE YOUNG SUN
- Journal of the Korean astronomical society = 천문학회지
- 33, n.3
- pp.165-172
- 2000
- 원문 바로보기
A baffle system for an airglow photometer, which will be on board the Korea Sounding Rocket-III(KSR-III), has been designed to suppress strong solar scattered lights from the atmosphere below the earth limb. Basic principles for designing a baffle system, such as determination of baffle dimensions, arrangement of vanes inside a baffle tube, and coating of surfaces, have been reviewed from the literature. By considering the constraints of the payload size of the KSR-III and the incident angle of solar light scattered from the earth limb, we first determined dimensions of a two-stage baffle tube for the airglow photometer. We then calculated positions and heights of vanes to prohibit diffusely reflected lights inside the baffle tube from entering into the photometer. In order to evaluate performance of the designed baffle system, we have developed a ray tracing program using a Monte Carlo method. The program computed attenuation factors of the baffle system on the order of <TEX>$10^{-6}$</TEX> for angles larger than <TEX>$10^{\circ}$</TEX>, which satisfies the requirements of the KSR-III airglow experiment. We have also measured the attenuation factors for an engineering model of the baffle system with a simple collimating beam apparatus, and confirmed the attenuation factors up to about <TEX>$10^{-4}$</TEX>. Limitation of the apparatus does not allow to make more accurate measurements of the attenuation factors.