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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 115/122
1141
- 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.
1142
- 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.
1143
- Lee, S.G.
- 天文學會誌 = The journal of the Korean Astronomical Society
- 14, n.2
- pp.73-78
- 1981
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On the basis of the recently available data, we have analysed the kinematical properties of nearby dwarfs, which are grouped by their spectral types and derived their ages from the kinematical properties. The discontinuities in the kinematical properties are found around late F stars, which appear to be caused mainly by the fact that the spectral groups earlier than late F are rather homogencous in age while the later ones are mixed by two different age group.
1144
- Hong, S.S.
- 天文學會誌 = The journal of the Korean Astronomical Society
- 14, n.1
- pp.37-42
- 1981
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In order to know how the magnetic field increases with density in interstellar clouds, we have analyzed observations of extinction and polarization for stars in the <TEX>${\rho}$</TEX> Oph molecular cloud complex. The size of grains in dense parts of the complex is estimated to be larger than the ones in diffuse interstellar clouds by about 15 percent in radii. Employing the Davis-Greenstein mechanism for grain alignment with this estimated grain size, we have put constraints on the exponent in the field-density relation <TEX>$B{\propto}n^x:1/5{\leq}x{\leq}1/3$</TEX>. It is concluded that magnetic field in gravitationally contracting clouds increases less steeply than the classical expectation based on the approximation of isotropic contraction with complete frozen-in flux.
1145
- Hyun, J.J.
- 天文學會誌 = The journal of the Korean Astronomical Society
- 14, n.2
- pp.51-54
- 1981
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The characteristic size and mass of galaxies as pre-galactic constraints on the Galactic evolution are reviewed and the general constraints for their existence in gravitationally bound systems are examined. Implications on the self-similar gravitational clustering are also discussed.
1146
- Lee, H.M.
- 天文學會誌 = The journal of the Korean Astronomical Society
- 14, n.1
- pp.19-35
- 1981
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Calculations of molecular number densities as a function of optical depth in selected umbral, penumbral and photospheric models predict penumbral enhancement of diatomic molecules containing carbon atoms, strong umbral enhancement of oxides, and moderate umbral enhancement of hydrides. The role of CO formation in an oxygen rich atmosphere is discussed.
1147
- Lee, S.W.
- 天文學會誌 = The journal of the Korean Astronomical Society
- 14, n.2
- pp.55-71
- 1981
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On the basis of observational constraints, particularly the relationship between metal abundance and cumulative stellar mass, a simple two-zone disk-halo model for the chemical evolution of our Galaxy was investigated, assuming different chemical processes in the disk and halo and the infall rates of the halo gas defined by the halo evolution. The main results of the present model calculations are: (i) The halo formation requires more than 80% of the initial galactic mass and it takes a period of <TEX>$2{\sim}3{\times}10^9$</TEX> yrs. (ii) The halo evolution is divided into two phases, a fast collapse phase (<TEX>$t=2{\sim}3{\times}10^8$</TEX> yrs) during which period most of the halo stars <TEX>$({\sim}95%)$</TEX> are formed and a later slow collapse phase which is characterized by the chemical enrichment due to the inflow of external matter to the halo. (iii) The disk evolution is also divided into two phases, an active disk formation phase with a time-dependent initial mass function (IMF) up to <TEX>$t{\approx}6{\times}10^9$</TEX> yrs and a later steady slow formation phase with a constant IMF. It is found that at the very early time <TEX>$t{\approx}5{\times}10^8$</TEX> yrs, the metal abundance in the disk is rapidly increased to <TEX>${\sim}1/3$</TEX> of the present value but the total stellar mass only to <TEX>${\sim}10%$</TEX> of the present value, finally reaching about 80% of the present values toward the end of the active formation phase.
1148
- Chun, M.S.
- 天文學會誌 = The journal of the Korean Astronomical Society
- 14, n.1
- pp.13-17
- 1981
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The observed radial UBV colour variations (both B-V and U-B) of some globular clusters are examined for correlations with radial variations in the integrated spectra. The results show that the presence of a radial colour gradient is correlated with the presence of a gradient of the CN (and possibly the G-band) line strength, in the sense that the CN (and possibly the G-band) is stronger in the centre (where the cluster is redder) and becomes weaker in the outer region of the cluster (where the cluster is bluer). This may suggest that a primordial abundance, possibly nitrogen and carbon gradient was set up in the early stage of cluster formation.
1149
- Hong, S.S.
- 天文學會誌 = The journal of the Korean Astronomical Society
- 14, n.2
- pp.89-93
- 1981
- 원문 바로보기
Weibull analyses given to the initial mass function (IMF) deduced by Miller and Scalo (1979) have shown that the mass dependence of IMF is an exp<TEX>$[-{\alpha}m]$</TEX>- form in low mass range while in the high mass range it assumes an exp<TEX>$[-{\alpha}\sqrt{m}]/\sqrt{m}$</TEX>-form with the break-up being at about the solar mass. Various astrophysical reasonings are given for identifying the exp<TEX>$[-{\alpha}m]$</TEX> and exp<TEX>$[-{\alpha}\sqrt{m}]/\sqrt{m}$</TEX> with halo and disk star characteristics, respectively. The physical conditions during the halo formation were such that low mass stars were preferentially formed and those in the disk high mass stars favoured. The two component nature of IMF is in general accord with the dichotomies in various stellar properties.
1150
- Ann, H.B.
- 天文學會誌 = The journal of the Korean Astronomical Society
- 14, n.1
- pp.1-11
- 1981
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Photoelectric drift scans of nearby galaxies, M106, M31 and M33 have been made at diurnal rate with the 61cm Cassegrain Reflector at Sobacksan Observing Station. Luminosity profiles of M106 and M31 show the asymmetries between east and west sides of the galaxies and the near side of each galaxy exhibits a larger B-V color than the far side. B-V color distribution in the central part of MI06 shows somewhat unusual feature of a blue center with red surrounding regions, and this is an opposite trend to the ordinary color distribution of most of external galaxies. B-V color of M31 is nearly constant in the central part of the galaxy while U-B color decreases as the distance from the center increases.