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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 72/119
711
- KIM JONGSOO
- Journal of the Korean astronomical society = 천문학회지
- 34, n.4
- pp.333-335
- 2001
- 원문 바로보기
We study the properties of supernova (SN) driven interstellar turbulence with a numerical magnetohydrodynamic (MHD) model. Calculations were done using the RIEMANN framework for MHD, which is highly suited for astrophysical flows because it tracks shocks using a Riemann solver and ensures pressure positivity and a divergence-free magnetic field. We start our simulations with a uniform density threaded by a uniform magnetic field. A simplified radiative cooling curve and a constant heating rate are also included. In this radiatively-cooling magnetized medium, we explode SNe one at a time at randomly chosen positions with SN explosion rates equal to and 12 times higher than the Galactic value. The evolution of the system is basically determined by the input energy of SN explosions and the output energy of radiative cooling. We follow the simulations to the point where the total energy of the system, as well as thermal, kinetic, and magnetic energy individually, has reached a quasi-stationary value. From the numerical experiments, we find that: i) both thermal and dynamical processes are important in determining the phases of the interstellar medium, and ii) the power index n of the <TEX>$B-p^n$</TEX> relation is consistent with observed values.
712
- KIM CHULHEE
- Journal of the Korean astronomical society = 천문학회지
- 33, n.2
- pp.75-80
- 2000
- 원문 바로보기
In order to identify the candidates of emission-line galaxies inside the southern Hydra Void, photo-graphic objective-prism observations with the UK Schmidt Telescope were carried out using the Tech-Pan films for five fields. All observed prism plates were scanned with the APM Facility and the scanned data was processed to determine the APM plate parameters and to draw spectra. For all galaxy spectra, the emission features, the distance between emission features of H<TEX>$\beta$</TEX>4861, [OIII]<TEX>${\lambda}{\lambda}$</TEX> 4959, 5007 and the overlapping by nearby objects were investigated by eyeballing. A total of 7 candidates of emission-line galaxies inside the Hydra Void were identified.
713
- PARK SEOK JAE
- Journal of the Korean astronomical society = 천문학회지
- 33, n.1
- pp.19-28
- 2000
- 원문 바로보기
In the earlier papers we analyzed the axisymmetric, nonstationary electrodynamics of the central black hole and a surrounding thin accretion disk in an active galactic nucleus. In this paper we analyze the axisymmetric, nonstationary electrodynamics of the black hole magnetosphere in a similar way. In the earlier papers we employed the poloidal component of the plasma velocity which is confined only to the radial direction of the cylindrical coordinate system. In this paper we employ a more general poloidal velocity and get the Grad-Shafranov equation of the force-free magnetosphere of a Kerr black hole. The equation is consistent with the previous ones and is more general in many aspects as it should be. We also show in more general approaches that the angular velocity of the magnetic field lines anchored on the accreting matter tends to become close to that of the black hole at the equatorial zone of the hole.
714
- 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.
715
- HAN CHEONGHO
- Journal of the Korean astronomical society = 천문학회지
- 33, n.2
- pp.89-95
- 2000
- 원문 바로보기
As an efficient method to detect blending of general gravitational microlensing events, it is proposed to measure the shift of source star image centroid caused by microlensing. The conventional method to detect blending by this method is measuring the difference between the positions of the source star image point spread function measured on the images taken before and during the event (the PSF centroid shift, <TEX>${\delta}{\theta}$</TEX>c,PSF). In this paper, we investigate the difference between the centroid positions measured on the reference and the subtracted images obtained by using the difference image analysis method (DIA centroid shift, <TEX>${\delta}{\theta}$</TEX>c.DIA), and evaluate its relative usefulness in detecting blending over the conventional method based on <TEX>${\delta}{\theta}$</TEX>c,PSF measurements. From this investigation, we find that the DIA centroid shift of an event is always larger than the PSF centroid shift. We also find that while <TEX>${\delta}{\theta}$</TEX>c,PSF becomes smaller as the event amplification decreases, <TEX>${\delta}{\theta}$</TEX>c.DIA remains constant regardless of the amplification. In addition, while <TEX>${\delta}{\theta}$</TEX>c,DIA linearly increases with the increasing value of the blended light fraction, <TEX>${\delta}{\theta}$</TEX>c,PSF peaks at a certain value of the blended light fraction and then eventually decreases as the fraction further increases. Therefore, measurements of <TEX>${\delta}{\theta}$</TEX>c,DIA instead of <TEX>${\delta}{\theta}$</TEX>c,PSF will be an even more efficient method to detect the blending effect of especially of highly blended events, for which the uncertainties in the determined time scales are high, as well as of low amplification events, for which the current method is highly inefficient.
716
- 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.
717
- 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.
718
- 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.
719
- BONG SU-CHAN
- Journal of the Korean astronomical society = 천문학회지
- 33, n.3
- pp.159-163
- 2000
- 원문 바로보기
We have investigated one dimensional steady flow model of a typical magnetic flux tube in the solar transition region constrained to observed Differential Emission Measure (DEM) for the average quiet-Sun deduced by Raymond & Doyle (1981) with a flux tube geometry conforming to Doppler shifts of UV lines measured by Chae, Yun & Poland (1998). Because local heating and filling factor in the transition region are not well known, we considered two extreme cases, one characterized by the filling factor= 1 ('filled-up model') and the other set by local heating=0 ('not-heated model'). We examined how much the heating is required for the flux tube by recomputing a model through adjustment of the filling factor in such a way that 'not-heated model' accounts for the observed DEM.
720
- 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.