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1968년 ~ 2023년까지 1,187 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 : 1,187건 (DB Construction : 1,187 Articles)
총 게시글 1,187건
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1091
- 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.
1092
- 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.
1093
- 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.
1094
- 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.
1095
- 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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1096
- 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.
1097
- Lee, Hyun-Sook
- 天文學會誌 = The journal of the Korean Astronomical Society
- 17, n.1
- pp.51-67
- 1984
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The well observed 8 open clusters, NGC 6530, 2264, 654, 129, 2168, Pleiades, Praesepe and Hyades were selected on the basis of photometric observation and proper motion study. The luminosity functions (LF) and mass functions (MF) of these clusters are different with cluster age and they could be divided into three age groups (t<<TEX>$10^7$</TEX> yrs, <TEX>$10^7$</TEX><t<<TEX>$10^8$</TEX> yrs, <TEX>$10^8$</TEX><t<<TEX>$10^9$</TEX> yrs). From these LF's and MF's, the mean LF and MF of the open clusters are derived and these functions suggest the time-dependent initial mass function (IMF) and the variation of observed MF with cluster age.
1098
- 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.
1099
- 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.
1100
- 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.