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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 114/123
1131
- Lee, Myung-Gyoon
- 天文學會誌 = The journal of the Korean Astronomical Society
- 18, n.1
- pp.15-31
- 1985
- 원문 바로보기
Making use of the arbitrary shock theory developed by Ulmschneider (1967, 1971) and Ulmschneider and Kalkofen (1978), we have calculated the dissipation rates of upward-travelling slow-mode acoustic shock waves in umbral chromospheres for two umbral chromosphere models, a plateau model by Avrett (1981) and a gradient model by Yun and Beebe (1984). The computed shock dissipation rates are compared with the radiative cooling rate given by Avrett (1981). The results show that the slow-mode acoustic shock waves with a period of about 20 second can heat the low umbral chromospheres travelling with a mechanical energy flux of <TEX>$2.6{\times}10^6\;erg/cm^2s$</TEX> at a height of <TEX>$300{\sim}400km$</TEX> above the temperature minimum region.
1132
- Lee, See-Woo
- 天文學會誌 = The journal of the Korean Astronomical Society
- 18, n.1
- pp.33-40
- 1985
- 원문 바로보기
1133
- Park, Chang-Bum
- 天文學會誌 = The journal of the Korean Astronomical Society
- 18, n.2
- pp.86-99
- 1985
- 원문 바로보기
A generalization of the original <TEX>${\ddot{O}}pik's$</TEX> cellular convection theory has been made to accomodate a rotating convective medium. With the use of the formulation, a set of rotating model envelopes of the sun and late type main sequence stars have been constructed under three different rotation periods. Their thermal structures are presented and characteristics of their convection are discussed in the context of stellar dynamo. In the present study it is noted that the rotational angular velocity increases in wards with depth, and its increase turns out to be about 6% at the bottom of the solar convection zone.
1134
- Lee, Sang-Gak
- 天文學會誌 = The journal of the Korean Astronomical Society
- 18, n.2
- pp.70-78
- 1985
- 원문 바로보기
From the kinematically unbiased sample of halo stars, the local mass density of halo dwarfs is estimated as <TEX>$6.0{\sim}6.3{\times}10^{-4}m_{\odot}/pc^3$</TEX> by adopting a color-magnitude relation and a mass-luminosity relation. The derived halo mass density is not much different from the results of previous studies, which were derived from the kinematically biased sample of halo stars. Therefore it is confirmed that the local mass density of halo stars is far less than that required by Ostriker-Peebles to stabilize the galactic disk against barlike instabilities.
1135
- Ann, Hong-Bae
- 天文學會誌 = The journal of the Korean Astronomical Society
- 18, n.2
- pp.79-85
- 1985
- 원문 바로보기
From the uvby, <TEX>$H_{\beta}$</TEX> photometry of intermediate population II F-stars in the catalogue of Olsen (1983), we derived age-metallicity relations for these stars, using Hejlesen's (1980) isochrone. The derived age-metallicity relations well coincide with the theoretical predictions by the unclosed two-zone model of Lee and Ann (1981). There are few extremely metal poor F-stars in the vicinity of the Sun, and it is very likely that the initial rapid metal enrichment in the galactic disk might have been processed through the fast collapse of the disk at the very early epoch.
1136
- Jung, Jae-Hoon
- 天文學會誌 = The journal of the Korean Astronomical Society
- 17, n.1
- pp.37-49
- 1984
- 원문 바로보기
UBV photoelectric observations were carried out for bright stars in M67 and the masses of clump stars and giant stars were derived in M67 and the other old open clusters, NGC 188, NGC 2420, NGC 2506 and IC 4651. The mean mass of clump stars in the five clusters ranges <TEX>$m=0.5{\sim}1.0m_{\odot}$</TEX>, and its ratio to the mean mass of giant stars is about 0.83. The number ratio of blue stragglers to the stars brighter than the turn-off of main sequence increases with cluster age whereas that of clump stars decreases with age. These results imply that the clump stars and blue stragglers are at the phase of horizontal branch evolution.
1137
- Lee, See-Woo
- 天文學會誌 = The journal of the Korean Astronomical Society
- 17, n.2
- pp.69-103
- 1984
- 원문 바로보기
Five different calibrations of metal abundances of globular clusters are examined and these are compared with metallicity ranking parameters such as <TEX>$(Sp)_c$</TEX>, <S>. Q39 and IR-indices. Except for the calibration <TEX>$[Fe/H]_H$</TEX> by the high dispersion echelle analysis. the other calibration scales are correlated with the morphological parameters of red giant branch. In the <TEX>$[Fe/H]_H$</TEX>-scale. the clusters later than <TEX>${\sim}F8$</TEX> have nearly a constant metal abundance. <TEX>$[Fe/H]_H{\simeq}-1.05$</TEX>, regradless of morphological characteristics of horizontal branch and red giant branch. By the two fundamental calibration scales of <TEX>$[Fe/H]_L$</TEX> (derived by the low dispersion analysis) and <TEX>$[Fe/H]_{{\Delta}s}$</TEX> (derived by the spectral analysis of RR Lyrae stars). the globular clusters are divided into the halo clusters with [Fe/H]<-1.0 and the disk clusters confined within the galactocentric distance <TEX>${\tau}_G=10\;kpc$</TEX> and galactic plane distance |z|=3 kpc. In this case the abundance gradient is given by d[Fe/H]/<TEX>$dr_G{\approx}-0.05\;kpc^{-1}$</TEX> and d[Fe/H]/<TEX>$d|z|{\simeq}-0.08\;kpc^{-1}$</TEX> within <TEX>${\tau}_G=20\;kpc$</TEX> and |z|=10 kpc, respectively. According to these characteristics of the spatial distribution of globular clusters. the chemical evolution of the galactic globular clusters can be accounted for by the two-zone (disk-halo) slow collapse model when the <TEX>$[Fe/H]_L$</TEX>-or <TEX>$[Fe/H]_{{\Delta}s}$</TEX>-scale is applied. In the case of <TEX>$[Fe/H]_H$</TEX>-scale, the one-zone fast collapse model is preferred for the evolution of globular clusters.
1138
- Kim, Sug-Whan
- 天文學會誌 = The journal of the Korean Astronomical Society
- 17, n.1
- pp.23-36
- 1984
- 원문 바로보기
From the PDS scanning, isophote maps and surface luminosity distributions for the late type spiral galaxy NGC 6946 were obtained. Surface luminosity distribution showed that this galaxy can be classified as the Freeman's type II, and the deep spheroidal component was caused as a result of the ring structure in the central part of NGC 6946. Physical parameters-total magnitude (<TEX>$M_T^B$</TEX>), effective radius (<TEX>$R_e^*$</TEX>), central surface magnitude <TEX>$U(0)_{CD}$</TEX>, length scale (<TEX>${\alpha}^{-1}$</TEX>), disk-to-bulge ratio (D/B) and mass-to-luminosity ratio (M/L)-were also calculated, and the results show that NGC 6946 belongs to Sc I type galaxy according to the DDO classification, and is to be a fair sample of classification statge T=6.
1139
- Chang, K.
- 天文學會誌 = The journal of the Korean Astronomical Society
- 17, n.1
- pp.15-22
- 1984
- 원문 바로보기
The transverse velocities of the gravitational lens system (galaxy plus a 'disturbing star') and their dependences on unkown properties of the source and the deflecting object are discussed. We have derived an analytic expression for the transverse velocity in terms of the velocities of the light source, the gravitational lensing galaxy and the 'disturbing star', and the observer. The results are then further applied to an estimate of the expectation value of the absolute transverse velocity and of the probable time scales of flux changes of the double QSO 0957+561A, B.
1140
- Hong, Seung-Soo
- 天文學會誌 = The journal of the Korean Astronomical Society
- 17, n.1
- pp.1-14
- 1984
- 원문 바로보기
Analyses of an integrated form <TEX>$N(\tau)={\int}_{\tau}^{\infty}n(\tau)d{\tau}$</TEX> of the distribution of cluster ages, rather than its differential form <TEX>$n(\tau)$</TEX>, demonstrate that the observed distribution has clusters older than about 500 million years in a significant excess over theoretical model distributions. Considerations on cluster disruption processes show that a single disruption time-scale, frequently employed by current theoretical models, is no longer an adequate parameter for describing survival probability of clusters over wide age range, because different initial conditions of these clusters produce corresponding spreads in their lifetimes. To take into account for the spread in initial conditions, we have introduced an age-dependent disruption time, and deduced its age-dependence from the present-day age distribution of clusters. Results show a distinct two-stage variation: The newly introduced disruption time stays constant at about 50 million years for clusters younger than about 100 million years, while for clusters older than that it increases monotonically with the cluster age. This leads us to conclude that clusters experience different types of disrupting causes as they get old.