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- The Korean Astronomical Society (The Korean Astronomical Society)
- 계간 (Quarterly)
- ISSN : 1225-4614 (ISSN : 1225-4614)
1225-4614
- DB구축현황 : 1,227건 (DB Construction : 1,227 Articles)
총 게시글 1,227건
페이지 105/123
1041
- 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.
1042
- 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.
1043
TIDAL EVOLUTION OF GLOBULAR CLUSTERS: THE EFFECTS OF GALACTIC TIDAL FIELD, DIFFUSION AND BLACK HOLES
- OH KAP SOO
- Journal of the Korean astronomical society = 천문학회지
- 27, n.1
- pp.61-76
- 1994
- 원문 바로보기
We investigate the dynamical evolution of globular clusters under the diffusion, the Galactic tide, and the presence of halo black holes. We compare the results with our previous work which considers the diffusion processes and the Galactic tide. We find the followings: (1) The black holes contribute the expansion of the outer part of the cluster. (2) There is no evidence for dependence on the orbital phase of the cluster as in our previous work. (3) The models of linear and Gaussian velocity distribution for the halo black holes do not show any significant differences in all cases. (4) The perturbation of black holes reduces the number of stars in lower energy regions. (5) There is a significant number of stars with retrograde orbits beyond the cutoff radius especially in the case of diffusion and the perturbation of black holes.
1044
- MINN Y. K.
- Journal of the Korean astronomical society = 천문학회지
- 27, n.1
- pp.31-44
- 1994
- 원문 바로보기
The 4.8GHz formaldehyde absorption line in the dark clouds in M17 and NGC 2024 regions has been mapped. In both nebulae, we detected two <TEX>$H_2CO$</TEX> line components. In M17, the 24km <TEX>$S^{-1}$</TEX> cloud is closely associated with the HII region located in front of the radio continuum source, and the 19km <TEX>$S^{-1}$</TEX> cloud is associated with the visual dark clouds with a larger extent which are closer to us. The 19km <TEX>$S^{-1}$</TEX> cloud has a mass motion approaching to the HII region. In both clouds, a velocity gradient from the north-east to the south-west directions is observed. The linewidth has no variation indicating no collapsing motion. In NGC 2024, the 9km <TEX>$S^{-1}$</TEX> feature is extended along the dark bar in front of the bright nebula and a weak second component at 13km <TEX>$S^{-1}$</TEX> is confined to the immediate vicinity of the radio source. Indications are that the 9km <TEX>$S^{-1}$</TEX> cloud is physically associated with the dark bar and the 13km <TEX>$S^{-1}$</TEX> cloud is located behind the radio source. The angular extent, the column density, and the total mass of the clouds are derived. The radial velocities of other molecular lines observed in these clouds are compared.
1045
- 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.
1046
- KIL HYO SUB
- Journal of the Korean astronomical society = 천문학회지
- 26, n.2
- pp.103-114
- 1993
- 원문 바로보기
We have analyzed a set of high resolution photographic line profiles of a Zeeman sensitive Fe I <TEX>$\lambda$</TEX> 6302.5 line taken with the Universal Birefringent Filter over a single round sunspot (SPO 5007) at the Sacramento Peak Solar Observatory. The observed spectra recorded on films are traced by PDS and the traced densities are converted to relative intensity by means of IRAF. The Stokes I and V profiles are then constructed by adding together and subtracting from each other the left and right handed circular polarizations, respectively. The reduced I and V profiles are analyzed by means of the coarse analysis(Auer et al.(1977), Skumanich and Lites(1987)) with the use of inversion technique. It is found that the umbral field strength is about 3000 gauss and the field distribution follows closely the emperical model proposed by Wittmann(1974).
1047
- ANN HONG BAE
- Journal of the Korean astronomical society = 천문학회지
- 26, n.1
- pp.13-32
- 1993
- 원문 바로보기
We have conducted BVI photographic surface photometry of four spiral galaxies NGC1087, NGC2715, NGC2844 and NGC3593, by making use of the Kiso Schmidt plates. Detailed examination of the morphological properties of the galaxies using isophotal maps and luminosity profiles showed that all the program galaxies have some peculiarities in their luminosity distributions. NGC1087 and NGC2715 have extremely small nuclei with inner rings which contain several bright HII regions. NGC2844 has a very large bulge whose luminosity dominates over the disk luminosity in all the radii. The I-band luminosity profile of NGC3593 shows shallower gradient than B- and V-band profiles. We were able to successfully decompose the luminosity profile into a bulge following de Vaucouleurs <TEX>$\gamma^{1/4}-law$</TEX> and an exponential disk only for NGC 3953. Other galaxies have more complicated luminosit profiles.
1048
- 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.
1049
- 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.
1050
- LEE SEE-WOO
- Journal of the Korean astronomical society = 천문학회지
- 26, n.1
- pp.47-64
- 1993
- 원문 바로보기
The photometric evolution of cluster stars are examined for six synthetic clusters in the age range from <TEX>$2.4\times10^6\;yr\;to\;7.6\times10^8yr$</TEX> by using the detailed evolutionary model calculation, and their results are compared with the observed integrated absolute magnitude and colors of 47 clusters. The reasonable agreements of the observed photometric parameters with the synthetic evolutionary sequences imply that there is a general form of time-dependent IMF including the noncoeval formation of stars and its detailed function is changed slightly with various environmental conditions of each primordial cloud.