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1968년 ~ 2025년까지 1,227 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 : 1,227건 (DB Construction : 1,227 Articles)
총 게시글 1,227건
페이지 106/123
1051
- 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.
1052
- 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.
1053
- 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.
1054
- 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.
1055
- 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.
1056
- 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.
1057
- KIM CHULHEE
- Journal of the Korean astronomical society = 천문학회지
- 26, n.2
- pp.115-134
- 1993
- 원문 바로보기
The light curve and radial velocity curve of multiperiodic dwarf cepheid VI719 Cyg (HD200925) with peculiar light curve have been reanalyzed in order to identify the oscillation modes to confirm the helium settling within the envelope. To do these, through the period search for the photometric and radial velocity data from the literature, two different periods were determined and the oscillation modes corresponding to the first and second periods were identified as the fundamental and first radial overtones. Hence the helium settling within the envelope was confirmed from the period ratio. The color excess, metallicity, effective temperature, and surface gravity corresponding to two different modes were determined and it was found that these parameters almost do not depend upon different oscillation mode. By utilizing the surface brightness method, we investigated the variation of angular diameter and radial displacement and it was found that the angular variation is very peculiar. Also by referring to the stellar models, mass and age were determined as <TEX>$2.7M_{\bigodot}$</TEX> and 0.42 Gyr respectively which make this variable star heavier and younger than other multimode dwarf cepheids. Preliminary spectroscopic CCD observations were carried out and it was found that Mg in VI719 Cygni is nearly solar abundent according to the analysis of <TEX>$5172.68{\AA}MgI$</TEX> line which is inconsistent with the photometric result. It was suggested that VI719 Cyg may be classified as a <TEX>$\rho$</TEX> Pup stars according to the photometric characteristics.
1058
- La, Daile
- 天文學會誌 = The journal of the Korean Astronomical Society
- 25, n.2
- pp.105-109
- 1992
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We show that spacing patterns of planets and satellites in the solar system are formulatable in a single form. It is suggested that a possible explanation for the rule might be the orbital resonance effect, which has existed at an earlier epoch of the solar (planet) system. By extrapolating the formulated spacing patterns beyond the sun-Pluto distance, we find the sun-Planet X distance falls in a range (<TEX>$46{\sim}79$</TEX>) A. U..
1059
- Chang, Kyong-Ae
- 天文學會誌 = The journal of the Korean Astronomical Society
- 25, n.2
- pp.79-90
- 1992
- 원문 바로보기
The physical properties of the flux factor K and its application are discussed in connection to the high amplification events. The effects due to random motions of stars in a foreground galaxy are examined in the frame work of moving caustics of gravitational microlenses.
1060
- Sung, Hwan-Kyung
- 天文學會誌 = The journal of the Korean Astronomical Society
- 25, n.2
- pp.91-104
- 1992
- 원문 바로보기
New photoelectric UBV Photometry of 112 stars in open cluster M35 field was obtained. The distance modulus and age of the cluster are <TEX>$9.^m3$</TEX>(725pc) and <TEX>$8.5{\times}10^7yrs$</TEX>, respectively. The internal differential reddening within the cluster is apparent.