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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 112/122
1111
- Chang, Kyong-Ae
- 天文學會誌 = The journal of the Korean Astronomical Society
- 19, n.2
- pp.63-68
- 1986
- 원문 바로보기
In this paper we deal with the orientation and the deformation of the circular light bundle passing in a static bounded gravitational field. The properties of caustic of the gravitational lens are discussed.
1112
- 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.
1113
- Lee, Sang-Gak
- 天文學會誌 = The journal of the Korean Astronomical Society
- 18, n.2
- pp.70-78
- 1985
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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.
1114
- Ann, Hong-Bae
- 天文學會誌 = The journal of the Korean Astronomical Society
- 18, n.2
- pp.79-85
- 1985
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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.
1115
- Lee, See-Woo
- 天文學會誌 = The journal of the Korean Astronomical Society
- 18, n.2
- pp.41-69
- 1985
- 원문 바로보기
For the well observed 16 globular clusters with known metal abundance (Z), the helium abundances (Y) and ages are determined by various methods, and the relations between Y, Z and age are examined. The luminosity <TEX>$L_{RR}$</TEX> of RR Lyrae stars is known to be dependent of evolutionary models and pulsation theory in the sense that the pulsation theory and horizontal branch (HB) models yield the anticorrelation between <TEX>$L_{RR}$</TEX> and Z whereas main sequence (MS) and red giant branch (RGB) models yield the direct correlation between them. Similarly the anticorrelation between Y and Z is obtained from the HB models and pulsation theory whereas the direct correlation between them is obtained when the RGB model is applied. The current evolutionary models yield the anticorrelation between Z and age of clusters whenever the direct correlation between Y and Z holds. However when the anticorrelation between Y and Z is applied for age determination, the similar age of clusters is obtained as shown by Sandage (1982b). The ages, which are determined by the fitting of C-M diagrams to isochrones in the (<TEX>$M_v$</TEX>, B-V)-plane, suggest the two different chemical enrichment processes, which could be accounted for by the disk-halo model for the chemical evolution of the Galaxy (Lee and Ann 1981). Also it is known that the R-method is very useful for Y-determination and the derived Y's show the increasing rate of <TEX>$\frac{{\Delta}Y}{{\Delta}Z}{\simeq}0.5$</TEX> which is comparable to the observed value of <TEX>$\frac{{\Delta}Y}{{\Delta}Z}{\simeq}0.3$</TEX> from HII regions and planetary nebulae by Peimbert and Torres-Peimbert (1976). In this case, the age-metallicity relation of globular clusters could be explained by the disk-halo model.
1116
- Jung, Jae-Hoon
- 天文學會誌 = The journal of the Korean Astronomical Society
- 18, n.1
- pp.1-13
- 1985
- 원문 바로보기
We present the data of photoelectric photometric observations of BW Vul carried out for four nights during the period of <TEX>$1982{\sim}1984$</TEX>. The light curves with asymmetric shape show a stillstand on the ascending branch at phase of <TEX>${\phi}{\approx}0.85$</TEX> just before the maximum light, and also the ampitude and shape of light curves are changed from night to night. Using all the published data, a new ephemeris of maximum time is derived, in which the period of light variation is <TEX>$P=0^d.20102977$</TEX> and its increasing rate is 2.2 see/century.
1117
- Lee, Myung-Gyoon
- 天文學會誌 = The journal of the Korean Astronomical Society
- 18, n.1
- pp.15-31
- 1985
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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.
1118
- Minn, Young-Key
- 天文學會誌 = The journal of the Korean Astronomical Society
- 18, n.2
- pp.100-110
- 1985
- 원문 바로보기
The HI features associated with HII regions and radio sources in the galactic-plane are searched in the Maryland-Green Bank Galactic 21-cm Line Survey. Among the twenty-eight such objects, twenty-five show HI depression features, two no feature, and an emission feature with excess HI brightness temperature. Most of these feature are surrounded by strong HI emissions. The depth of the HI depression is proportional to the radio continuum brightness temperature. The angular dimensions of the HI feature and radio source are comparable. The small HI depressions shown at the positions of HII region located in the outer solar circle are considered to be HI self-absorption features of very cold HI gas.
1119
- Lee, See-Woo
- 天文學會誌 = The journal of the Korean Astronomical Society
- 18, n.1
- pp.33-40
- 1985
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1120
- 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.