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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 114/122
1131
- Chun, Mun-Suk
- 天文學會誌 = The journal of the Korean Astronomical Society
- 16, n.1
- pp.1-5
- 1983
- 원문 바로보기
Four HII regions of the Sd galaxy NGC 7793 were observed using AAT/IPCS. From these spectra we determined abundances of the elements using observed emission lines and electron temperatures. The calculated abundances show that this galaxy does not show any significant radial abundance gradient. The mean oxygen abundance is very much like the Orion nebulae and the nitrogen abundance is similar to the late type barred spiral galaxy NGC 1313.
1132
- Park, Young-Deuk
- 天文學會誌 = The journal of the Korean Astronomical Society
- 16, n.2
- pp.31-42
- 1983
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Making use of a relation proposed by Wielen (1977), a new empirical relation between Call emission flux and stellar age is derived by analyzing Wilson and Woolley's spectroscopic data (1970) of late type main sequence stars (K0-M5) and kinematic properties of those stars given by Gliese (1969). The proposed relation shows that the emission flux excess of the Call H-K lines, <TEX>$F_k'+F_k'$</TEX> introduced by Linsky et al. (1979) decreases with stellar age <TEX>$\tau$</TEX> as <TEX>$\tau^{-0.51}$</TEX>, consistent with the inverse square law as noted by Skumanich (1972).
1133
- Lee, Sang-Gak
- 天文學會誌 = The journal of the Korean Astronomical Society
- 16, n.2
- pp.55-63
- 1983
- 원문 바로보기
From UBVRI photometry and space motion data of 232 late type dwarf stars, it is found that for the stars of (R-I)<0.5, <TEX>$\Delta$</TEX>(U-B) and <TEX>$\Delta$</TEX>(B-V) color excesses are correlated with their orbital eccentricities. Therefore, <TEX>$\Delta$</TEX>(U-B) and <TEX>$\Delta$</TEX>(B-V) color excesses can be used as possible photometric abundance indicators for the stars of (R-I)<0.5. For the stars of (R-I)<TEX>${\geq}$</TEX>0.5, the correlation between color excess and orbital eccentricity is not clear. However, it is interesting to note that the high orbital eccentricity stars show some blue deficiencies and these blue deficiencies seem to be correlated with orbital eccentricity.
1134
- Lee, See-Woo
- 天文學會誌 = The journal of the Korean Astronomical Society
- 16, n.2
- pp.43-54
- 1983
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The present day mass functions of main sequence stars in the well observed open clusters, Hyades, Praesepe, Pleiades, NGC 654 and NGC 6530 arc derived and compared with those computed from the model of time-dependent initial mass function and star formation rate. The agreements between the observed and computed present day mass functions suggest the importance of fragmentation process at the early phase and fragment interaction at the later phase of cluster evolution. This process of star formation is different from that related to the evolution of the solar neighborhood, and also could explain the lack of low mass stars observed in some open clusters.
1135
- Ann, Hong-Bae
- 天文學會誌 = The journal of the Korean Astronomical Society
- 15, n.1
- pp.1-7
- 1982
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The luminosity functions of 12 open clusters are derived for which their membership and the colors of their individual stars have been established by detailed proper motion study and high quality photometric work. The resulting luminosity functions of these clusters are presented and discussed.
1136
- Lee, See-Woo
- 天文學會誌 = The journal of the Korean Astronomical Society
- 15, n.2
- pp.71-77
- 1982
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According to the star formation rate and metal enrichment rate given by the disk-halo model of Lee and Ann (1981), the two different forms of time-dependent initial mass function (IMF) and the present day mass function (PDMF) of nearby stars have been examined. It was shown that the constraint for the initial rapid metal enrichment requires the time-dependence of IMF at the very early phase (<TEX>$t{\lesssim}5{\times}10^8$</TEX> yrs) of the solar neighborhood. The computed PDMF's show that the PDMF is nearly independent of any specific functional form of IMF as long as the latter includes a Gaussian distribution of log m. This result is due to the very small fractional mass <TEX>$({\times}5%)$</TEX> of stars formed at the very early period during which the IMF is time-dependent. The computed PDMF suggests the presence of more numerous low mass stars than shown in Miller and Scalo's (1979) PDMF, supporting the possibility of the existence of low-velocity M dwarfs. According to the number distribution of stars with respect to [Fe/H], the mean age of these low mass star must be very old so as to yield the mean metal abundance <TEX>$\bar{[Fe/H]}{\approx}-0.15$</TEX> for the stars in the solar neighborhood.
1137
- Lee, Sang-Gak
- 天文學會誌 = The journal of the Korean Astronomical Society
- 15, n.2
- pp.49-58
- 1982
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The UBVRIHKL magnitudes on Johnson system and space motions of M dwarf stars have been collected. This sample of M stars have been distinguished on a purely kinematical basis; the one with e<0.15, young disk population, with 0.15<e<0.3 old disk population, and with e>0.3 halo population. On the color-color diagrams and the color excess-orbital eccentricity diagrams, there is no distinction between the old disk stars and the young disk stars. However (I-H) color could be used to distinguish halo stars from young and old disk stars and the color excesses, <TEX>${\Delta}(U-B),\;{\Delta}(B-V),\;{\Delta}(V-R),\;{\Delta}(H-K),\;{\Delta}(K-L),\;and\;{\Delta}(B-R)$</TEX> can be used as abundance indicators only for the halo stars. But these color excesses which are measures of blue excesses, are positive for the halo stars with smaller eccentricities and become negative for those with larger eccentricities.
1138
- Kim, Dong-Woo
- 天文學會誌 = The journal of the Korean Astronomical Society
- 15, n.1
- pp.9-18
- 1982
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To derive the distributions of electron density, temperature and gas-phase metal abundances within the Orion Nebula, we have performed a non-LTE analysis to the radio observations of hydrogen recombination lines and continuum flux over the frequency range from 0.1GHz to 100GHz. We have explicitly included the thermal balance condition in our analysis, hence our derived distributions have their internal consistencies. This enables us to derive the radial distribution of Oxygen and Nitrogen. The gas-phase concentrations of these cooling agents show about the solar values at the very central part of the nebula, then, decrease slowly outward, and finally become about one quarter of the solar values in the outer extended envelope. Such an outward decrease is interpreted as an outward increase of dust concentrations in the Orion.
1139
- Chun, Mun-Suk
- 天文學會誌 = The journal of the Korean Astronomical Society
- 15, n.1
- pp.41-48
- 1982
- 원문 바로보기
PDS was used to get the structure of two barred spiral galaxies NGC 1313 and NGC 1365. The result shows that NGC 1365 has both a deep spheroidal component and an exponential disk, but NGC 1313 has only an prominent exponential component. The luminosity profiles indicate that KGC 1313 is in type I and NGC 1365 belongs to type II. The length scales <TEX>$({\alpha}^{-1})$</TEX> were derived from the exponential luminosity distributions as 1.64 kpc for NGC 1313 and 2.49kpc for KGC 1365.
1140
- Yoon, Tae-Seog
- 天文學會誌 = The journal of the Korean Astronomical Society
- 15, n.2
- pp.59-70
- 1982
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We have observed 85 UBV standard stars(V<6) with SNU photoelectric photometer system and 24' Cassegrain reflector at Sobaeksan Observing Station during the period between January and May, 1980 in order to examine the photometer system and to determine atmospheric extinction coefficients. From five night observations, the following results were obtained: (1) The set of filters(V=2mm GG 495, B=2mm GG 385+1mm BG 12, U=2mm UG 2) is better than the other filter set used in our tests on the basis of linear instrumental calibrations for V and B filters. (2) The SNU detecting system is very stable within <TEX>${\sigma}=0.002$</TEX> in magnitude in a night but the variation in its stability from night to night is not negligible. (3) The extinction coefficients were derived from two different methods and we have found no systematic seasonal variation in the extinction coefficients although the mean dispersion is considerable.