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- 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
- PYO TAE SOO
- Journal of the Korean astronomical society = 천문학회지
- 27, n.2
- pp.119-132
- 1994
- 원문 바로보기
The BVR CCD photometry was performed for the globular cluster M13 down to <TEX>$V=19^m$</TEX> over the region from the center to the west 13 arcmin and the CMD of M13 is investigated. The major photometric error in the crowded field which is due to the variation in the sky background was corrected by the median filtering method and the direct sky method. Some characteristics of the CMD of M13 obtained in the present study are as follows: Firstly, the distribution of stars on the CMD is well consistent with the mean lines of Sandage(1970) along the red giant branch(RGB), horizontal branch(HB) and asymtotic giant branch(AGB). Secondly, some gaps exists along the RGB and blue horizontal branch(BHB). Thirdly, the UV-bright stars are more concentrated at the inner region of the cluster.
1022
- CHAE JONG-CHUL
- Journal of the Korean astronomical society = 천문학회지
- 27, n.2
- pp.191-201
- 1994
- 원문 바로보기
We propose to use the entropy of power spectra defined in the frequency domain for the deconvolution of extended images. Spatial correlations requisite for extended sources may be insured by increasing the role of power entropy because the power is just a representation of spatial correlations in the frequency domain. We have derived a semi-analytical solution which is found to severely reduce computing time compared with other iteration schemes. Even though the solution is very similar to the well-known Wiener filter, the regularizingng term in the new expression is so insensitive to the noise characteristics as to assure a stable solution. Applications have been made to the IRAS <TEX>$60{\mu}m\;and\;100{\mu}m$</TEX> images of the dark cloud B34 and the optical CCD image of a solar active region containing a circular sunspot and a small pore.
1023
- 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.
1024
- 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.
1025
- 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.
1026
- 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.
1027
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.
1028
- 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.
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
- 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).