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- 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 101/119
1001
- 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.
1002
- 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.
1003
- 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.
1004
- 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.
1005
- 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.
1006
- LA DAILE
- Journal of the Korean astronomical society = 천문학회지
- 26, n.2
- pp.135-139
- 1993
- 원문 바로보기
Events of eclipses as well as other major astronomical events observable in the eastern sector of Asian continent are computed and checked with astronomical records of antiquity. Particular attention was given to two types of the events recorded in remaining records of Dangun Chosun Period (DCP): (1) concentration of major planets near the constellation of Nu-Sung <TEX>$(\beta\;Aries)$</TEX> and (2) a large ebb-tide. We find them most likely to have occurred in real time. i.e., when the positions of the sun, moon, and planets happen to be aligned in the most appropriate position. For solar eclipses data, however, we find among 10 solar eclipse events recorded, only 6 of them are correct up to months, implying its statistical significance is no less insignificant. We therefore conclude that the remaining history books of DCP indeed contains important astronomical records, thereby the real antiquity of the records of DCP cannot be disproved.
1007
- 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.
1008
- LEE SANG-GAK
- Journal of the Korean astronomical society = 천문학회지
- 26, n.2
- pp.141-152
- 1993
- 원문 바로보기
The sample of sub dwarfs are selected from LHS catalogue on the bases of the reduced proper motion diagram utilizing Chui criteria, and confirmed with the available photometric and/or kinematic data. Among them, 20 sub dwarfs have trigonometric parallaxes with accuracy better than <TEX>$20\%$</TEX>. The colorabsolute magnitude relation is derived with them. By adopting this color-magnitude relation and <TEX>$V/V_m$</TEX> method, we have derived the sub dwarf luminosity function over the absolute magnitude range of <TEX>$M_v$</TEX>= 4.5 and 9.5. This halo luminosity function is consistent with that of Eggen(1987). By adopting the available mass-luminosity relations for halo stars, we have found that the halo IMF is steeper than disk IMFs of Scalo(1986) and Salpter(1955) in this small mass region.
1009
- LEE C. W.
- Journal of the Korean astronomical society = 천문학회지
- 26, n.1
- pp.73-78
- 1993
- 원문 바로보기
We have mapped the <TEX>$C_3H_2\;2_{12}-1_{01}$</TEX> transition line toward the Sgr A molecular cloud on a 1' grid spacing and derived <TEX>$C_3H_2$</TEX> column densities of <TEX>$3\~7\times10^{14}\;cm^{-2}$</TEX> for molecular clouds of Sgr A. The fractional abundances of <TEX>$C_3H_2$</TEX> relative to <TEX>$H_2$</TEX> are obtained to be <TEX>$3\~6\times10^{-9}$</TEX>, which are slightly lower than that for the cold dark cloud TMC-1 but are enhanced by factors of 5-60 compared to those for Sgr B2 and the Orion extended ridge. We also estimate from the <TEX>$C_3H_2$</TEX> column densities total masses of <TEX>$\~10^6\; M_\bigodot$</TEX> for two clouds (M - 0.13 - 0.08 and M - 0.02 - 0.07), which are thought to be close to the virial equilibrium. We suggest that the large abundance of <TEX>$C_3H_2$</TEX> in Sgr A may be partly due to the activities of the Galactic center.
1010
- KANG HYESUNG
- Journal of the Korean astronomical society = 천문학회지
- 26, n.1
- pp.1-12
- 1993
- 원문 바로보기
In order to explore the time dependence of the closure parameters of the two-fluid calculations for supernova remnants and the terminal shocks of stellar winds, we have considered a simple model in which the time evolution of the cosmic-ray distribution function was followed in the test-particle limit using the Bohm diffusion model. The particles are mostly accelerated to relativistic energy either in the free expansion phase of the SNRs or in the early phase of the stellar winds, so the evolution of the closure parameters during these early stages is substantial and should be followed correctly. We have also calculated the maximum momentum which is limited by either the age or the curvature of these spherical shocks. We found that SNRs expanding into the medium where the gas density decreases with the distance from the explosion center might be necessary to explain the observed power-law distribution of the galactic cosmic rays. The energy loss due to the escaping energetic particles has been estimated for the terminal shocks of the stellar winds.