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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 113/122
1121
- 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.
1122
- 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.
1123
- Kim, Sug-Whan
- 天文學會誌 = The journal of the Korean Astronomical Society
- 17, n.1
- pp.23-36
- 1984
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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.
1124
- 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.
1125
- Chang, K.
- 天文學會誌 = The journal of the Korean Astronomical Society
- 17, n.1
- pp.15-22
- 1984
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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.
1126
- Hong, Seung-Soo
- 天文學會誌 = The journal of the Korean Astronomical Society
- 17, n.2
- pp.115-125
- 1984
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Effect of magnetic field on the thermal instability is studied in the radiatively cooling region behind an interstellar shock of moderate propagation velocity (<TEX>${\sim}10\;km/sec$</TEX>). It is shown that the presence of interstellar magnetic field of a few micro gauss is very effective in preventing the thermal instability from building-up density concentration. In the absence of magnetic field, the shock-induced thermal instability amplifies preshock density inhomogeneity by more than an order of magnitude. However, in the presence of magnetic field, the amplified density contrast is shown to be only a factor 2.
1127
- Woo, Jong-Ok
- 天文學會誌 = The journal of the Korean Astronomical Society
- 17, n.2
- pp.104-114
- 1984
- 원문 바로보기
The effective temperatures, <TEX>$T_{eff}$</TEX> (flux) of 52 early type stars are derived from de-reddened monochromatic and integrated fluxes obtained by absolute spectrophotometry, using the method of graphical analysis pioneered by Blackwell and Shallis (1977), similar to that of Underhill (1982) and Tobin (1983). We also estimated the effective temperatures, <TEX>$T_{eff}$</TEX> (comp) of the same stars by comparing their de-reddened energy distributions with those of the LTE model atmospheres by Kurucz (1979). The effective temperatures derived from these two methods are found to be in good agreement, confirming that they are effective for the estimation of effective temperatures of early type stars.
1128
- Lee, Sang-Gak
- 天文學會誌 = The journal of the Korean Astronomical Society
- 16, n.1
- pp.23-30
- 1983
- 원문 바로보기
About two hundred stars within 50 pc from the sun, whose tangential velocity larger than 100 km/sec, have been selected on the basis of their proper motions and trigonometric parallaxes. A list of them along with their photoelectric UBV data and spectral types is given. The criterion on the tangential velocity, <TEX>$v_t$</TEX> > 132 km/sec, was adopted for selection of high-velocity stars. The H-R diagram of these nearby high-velocity stars resembles that of a globular cluster, with the turnoff around <TEX>$B-V{\approx}0.35$</TEX> and <TEX>$M_v{\approx}4.0$</TEX>, and the subdwarfs among these high-velocity stars are fainter than the main-sequence stars of Hyades by the amount of <TEX>$1^m.25{\pm}0^m.30$</TEX> in the region with B-V < 1.40 on the average.
1129
- Yun, Hong-Sik
- 天文學會誌 = The journal of the Korean Astronomical Society
- 16, n.1
- pp.19-22
- 1983
- 원문 바로보기
The reduced profiles of <TEX>$C_2$</TEX> 5150.56, CN 3864.32, MgH 5150.20 and FeI 5150.84 lines, representing the penumbra, the penumbra-umbra boundary and the umbra of spa 6403 have been analyzed by comparing them with the synthetic profiles computed from a set of umbral and penumbral models. The results are presented and discussed. It is suggested that there may be a significant lateral flow of pbotospheric radiation into the umbral and penumbral regions of the sunspots.
1130
- Kwon, Suk-Minn
- 天文學會誌 = The journal of the Korean Astronomical Society
- 16, n.1
- pp.7-17
- 1983
- 원문 바로보기
During the period between January and November in 1982, UBV photoelectric observations were made for 48 stars in NGC 2264, 66 stars in IC 1805 and 22 stars in IC 348. From these observations, various physical parameters such as distance, mean color excess, total-to-selective extinction ratio and mean age of the clusters were determined. Making use of these parameters, the star formation rates were examined for IC 348 and NGC 2264. The overall formation rate is found to be increase rapidly during the period of the active star formation. The age spread (ranging from <TEX>$5\times10^6$</TEX> yrs to <TEX>$10^7$</TEX> yrs) of stars in a given cluster appears to be real which occurs in the extremely young open clusters.