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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 103/122
1021
- SEON KWANG IL
- Journal of the Korean astronomical society = 천문학회지
- 27, n.1
- pp.45-53
- 1994
- 원문 바로보기
We present the calculation of X -ray spectra produced through Compton scattering of soft X-rays by hot electrons in the spherical shell geometry, using fully relativistic Monte Carlo simulation. With this model, we show that the power-law component, which has been observed in the low luminosity state of low-mass X-ray binaries (LMXBs), is explained physically. From a spectral. analysis, we find that spectral hardness is mainly due to the relative contribution of scattered component. In addition, we see that Wi en spectral features appear when the plasma is optically thick, especially in the high energy range, <TEX>$E{\gtrsim}100keV$</TEX>. We suggest that after a number of scattering the escape probability approaches an asymptotic form depending on the geometry of the scattering medium rather than on the initial photon spectrum.
1022
- MINH Y. C.
- Journal of the Korean astronomical society = 천문학회지
- 27, n.1
- pp.55-60
- 1994
- 원문 바로보기
The 3mm transitions to CO, <TEX>$^{13}CO,\;CS,\;HCO^+$</TEX>, and HCN have been observed toward the compact HII regions in W58 using the 14m Daeduk Radio Telescope (DRT). Some of the observed lines show high-velocity wings resulted from outflowing materials of the compact HII regions. We derive the beam averaged column densities of the observed species and compare their relative abundances. The <TEX>$HCO^+$</TEX> abundance appears to be smaller by about an order of magnitude than those of 'typical' quiet molecular clouds. CS may be a good reference molecule in comparing relative abundances in different physical conditions.
1023
- LEE YOUNGUNG
- Journal of the Korean astronomical society = 천문학회지
- 27, n.2
- pp.147-158
- 1994
- 원문 바로보기
We have obtained high angular resolution maps toward a molecular cloud associated with an HII region S287 and studied mainly kinematics of the cloud. The mapped region is 1.5 square degrees of the cloud in the transitions of <TEX>$^{12}CO\;and\;^{13}CO\;J=1-0$</TEX>. We have obtained a large range of mass, <TEX>$1.3\times10^4M_\bigodot$</TEX>, to <TEX>$7.2{\times}10^4M_{\bigodot}$</TEX> using three different techniques. The S287 molecular cloud shows a very disturbed feature: velocity field of the cloud is very complicated, and shows several arcs. It is likely that the southern part of cloud is being disrupted by the residing HII region S287 as well as external perturbing sources. In addition to an HII region, five bipolar outflows are also disturbing the molecular gas significantly. The large virial mass and the very disturbed morphology may reflect the fact that the cloud is not gravitationally bound system, as in the case of nearby giant molecular cloud (GMC) G216-2.5. The several arc structure and the filamentary features are possibly driven by external strong stellar winds, and these external perturbing sources may be driving the second generation of star-forming activities on the edges of the S287 molecular cloud.
1024
- KIM W. -T.
- Journal of the Korean astronomical society = 천문학회지
- 27, n.1
- pp.13-29
- 1994
- 원문 바로보기
We have constructed a 3-dim hydrodynamics code called BTSPH. The fluid dynamics part of the code is based on the smoothed particle hydrodynamics (SPH), and for its Poisson solver the binary tree (BT) scheme is employed. We let the smoothing length in the SPH algorithm vary with space and time, so that resolution of the calculation is considerably enhanced over the version of SPH with fixed smoothing length. The binary tree scheme calculates the gravitational force at a point by collecting the monopole forces from neighboring particles and the multipole forces from aggregates of distant particles. The BTSPH is free from geometric constraints, does not rely on grids, and needs arrays of moderate size. With the code we have run the following set of test calculations: one-dim shock tube, adiabatic collapse of an isothermal cloud, small oscillation of an equilibrium polytrope of index 3/2, and tidal encounter of the polytrope and a point mass perturber. Results of the tests confirmed the code performance.
1025
- LEE SANG GAK
- Journal of the Korean astronomical society = 천문학회지
- 27, n.2
- pp.133-146
- 1994
- 원문 바로보기
We have detected a SiO maser line (v=1, J=2- 1) for 15 stars out of about 80 long period variables in the wide range of period. No new sources are detected; all detected sources are variables with period longer than 300 days; no evidence is found that the dust grains in the outer envelope have influenced on this line. The time variation of this maser line for 7 stars, T Cep, <TEX>${\mu} Cep$</TEX>, U Her, R Leo, R Lmi, U Ori, and R Ser is observed and compared with optical light curve at the same epoch of maser observation. No universial relation between the time variation and the optical light curve is found. It implies that the radiation from a central star does not much play an important role for the direct pumping of the SiO maser line.
1026
- LEE YOUNGUNG
- Journal of the Korean astronomical society = 천문학회지
- 27, n.2
- pp.159-175
- 1994
- 원문 바로보기
We have mapped the whole extent of a dark cloud Lynds 1251 in the emission of the J=1-0 transitions of <TEX>$^{12}CO\;and\;^{13}CO$</TEX> using FCRAO's fifteen-beam array receiver in high angular resolution of 50'. We have derived physical parameters of L1251, discussed three different mass estimate techniques, and obtained a large range of mass, 600 to <TEX>$6,000M_\bigodot$</TEX>, depending on the techniques. The factor of 10 discrepancy between the virial and LTE masses is much larger than expected based on the uncertainties residing in two methods. The large virial mass may reflect the fact that L1251 is not gravitationally bound system as in the case of dark clouds in solar neighborhood. Two outflows are affecting the dynamics of cloud significantly but not enough to reshape the whole extent of the cloud. The small cloud, 'Stripe', which is apparently connected with main cloud, is not likely to be associated with L1251. The velocity gradient composed on this small cloud may be driven by other unknown sources. It is found that L1251 cloud itself is very quiescent except the two bipolar outflow regions.
1027
- CHUNG HYUN SOO
- Journal of the Korean astronomical society = 천문학회지
- 27, n.1
- pp.1-11
- 1994
- 원문 바로보기
We have observed the emission of <TEX>$HC_3N$</TEX> J=4-3, 5-4,10-9 and 12-11 transitions toward the Sgr B2 central region in an area of <TEX>$150'\times150'$</TEX> with resolutions of 16'-48'. The intensities and central velocities of line profiles show significant variations with positions. In contrast to the intensities of the low J-level transitions which gradually increase from the central source toward the outside region, the <TEX>$HC_3N$</TEX> emission of the high J-level transition become stronger toward 'the central radio continuum source MD5. Systematic change in the radial velocity of each line profile occurs along north-south direction. There are a few peaks in most line profiles, and these indicate that there are multiple velocity components along the line of sight. Distributions of excitation temperature and column density which were estimated from the excitation calculations show the existence of a small <TEX>$(1\times2pc),\;hot\;(T_{ex}>50K)$</TEX> core which contains two temperature peaks at-15' east and north of MD5. The column density of <TEX>$HC_3N\;is\;(1-3)\times10^{14}cm^{-2}$</TEX> Column density at distant position from MD5 is larger than that in the central region. We have deduced that this 'hot-core' has a mass of 105M 0, which is about an order of magnitude larger than those obtained by previous studies.
1028
- PARK SEOK JAE
- Journal of the Korean astronomical society = 천문학회지
- 27, n.1
- pp.77-80
- 1994
- 원문 바로보기
Variability of the emission-line spectra of active galactic nuclei is now a well-known phenomenon. This remains to be fully explained by a theoretical model of the central engine in an active galactic nucleus. Since the magnetic field lines are anchored on the accreting matter, they continuously fall on the event horizon of the central supermassive black hole and increase the net field strength of the hole magnetosphere. The field strength, however, cannot increase without an upper limit and, therefore, it will be decreased by some unknown processes. In this paper we discuss that these increasing and decreasing modes can be repeated periodically and explain the variability of power output, therefore, variability of active galactic nuclei.
1029
- SONG H. J.
- Journal of the Korean astronomical society = 천문학회지
- 26, n.1
- pp.65-72
- 1993
- 원문 바로보기
Using the Daeduk Radio Telescope, we have observed <TEX>$J=1\rightarrow0$</TEX> transitions of 1<TEX>$^{12}CO,\;^{13}CO\;and\;C^{18}O$</TEX> toward OMC-l. The column densities of <TEX>$1\~5\times10^{17}\;cm^{-2}\;and\;1\~3\times10^{16}\;cm^{-2}$</TEX> have been derived, for <TEX>$^{13}CO$</TEX> and <TEX>$C^{18}O$</TEX>, respectively, in the <TEX>$11'\times11'$</TEX> region centered at Orion - KL. The double isotope ratio <TEX>$[^{13}CO]/[C^{18}O]$</TEX> was found to be larger than the cosmic abundance ratio by factors of <TEX>$2\~10$</TEX> which may result from the chemical fractionation effect.
1030
- LEE HAESHIM
- Journal of the Korean astronomical society = 천문학회지
- 26, n.1
- pp.79-81
- 1993
- 원문 바로보기
We calculated the solar monopole abundance limit by comparing the observed solar neutrino flux and the calculation of non-fusion solar neutrino flux produced by Rubakov process in the solar core. We included the produced meson's enhancement effects by the surrounding ions in the solar core. We find that the monopole number <TEX>$N_M<1.9\times10^{20}(1mb/{\sigma}0)$</TEX>, where <TEX>${\sigma}0$</TEX> is the characteristic proton decay cross section of Rubakov process. This is similar or stronger than strong limits obtained from neutron star's luminosity.