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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 104/122
1031
- 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.
1032
- 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.
1033
- 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.
1034
- 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.
1035
- 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.
1036
- 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.
1037
- 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.
1038
- CHOI JEONG TAE
- Journal of the Korean astronomical society = 천문학회지
- 26, n.1
- pp.33-45
- 1993
- 원문 바로보기
We have conducted surface photometry of a spiral galaxy NGC4419, by making use of photographic plates in U, B, V and R-bands taken by 105cm Schmidt Camera at Kiso Observatory. Two dimensional surface brightness distributions as well as luminosity profiles along the major axis are examined in detail to decipher the morphological properties of the galaxy. Analysis of the color distributions of NGC4419 shows that B-V and U-B colors remain constant throughout the galaxy with a weak trend of blue bulge in B-V color. The blue bulge might indicate an active star formation in the nucleus of NGC4419. For a quantitative analysis of the luminosity distribution of NGC4419, the observed luminosity profiles are decomposed into bulge and disk components, assuming the bulge component to follow de Vaucouleurs <TEX>$\gamma^{1/4}-law$</TEX> while the disk component is assumed to be exponential. The fitting generally fails at the central part and at the shoulder near r = 15' where bulge and disk components overlap. The failure at the central part cannot be attributed wholly by the seeing disk since the core-radius of the central plateau is much larger than the width of point spread function. The failure at shoulder could be due to the luminosities from the spiral arms.
1039
- MINH Y. C.
- Journal of the Korean astronomical society = 천문학회지
- 26, n.2
- pp.99-101
- 1993
- 원문 바로보기
We have searched for the 2 mm transitions of <TEX>$H_2COH^+(2_{02}-1_{01})$</TEX> and <TEX>$H_2\;^{13}CO(2_{02} - 1_{01},\; 2_{12}-1_{11},\;and\;2_{11}-1_{10})$</TEX> toward the dense interstellar molecular clouds Orion A, TMC-1 and L134N using the FCRAO 14 m telescope. None of the transitions have been detected except the <TEX>$H_2\;^{13}CO$</TEX> transitions toward Orion-KL. We set upper limits for the abundances of the protonated formaldehyde ion <TEX>$(H_2COH^+)$</TEX>, which are close to the abundances expected from ion-molecule chemistry.
1040
- YUN HONG SIK
- Journal of the Korean astronomical society = 천문학회지
- 26, n.2
- pp.89-98
- 1993
- 원문 바로보기
Magnetostatic models of starspots of late type main sequence stars<TEX>$(G5V\~K5V)$</TEX> have been constructed to investigate their physical characteristics by using the similarity law suggested by Schluter and Temesvary(1958) and later employed by Deinzer(1965) and Yun(1968). The starspots are assumed to be single, circular and in horizontal magnetostatic equilibrium. In the present study we considered only those model spots whose area covers less than <TEX>$12\%$</TEX> of the entire stellar surface as suggested by observations. The computed surface field strength of our model spots ranges from <TEX>$10^3$\;to\;several\;10^3$</TEX> gauss and their magnetic flux is found to be <TEX>$10\~100$</TEX> times that of sunspots. The field strength is sensitive to spectral type, which increases with later spectral type. In contrast to the field strength, the area of starspots depends strongly on the total magnetic flux. Finally, it is noted that the computed field strength of model spots belonging to <TEX>$G0V\~G5V$</TEX> falls below the equipartition field strength at their parent stellar surface unless the coverage is less than <TEX>$2\%$</TEX>. This suggests that the observed spot on <TEX>$G0V\~G5V$</TEX> stars is likely to be a group of small starspots.