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- 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
페이지 112/119
1111
- 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.
1112
- 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.
1113
- 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.
1114
- Chun, Mun-Suk
- 天文學會誌 = The journal of the Korean Astronomical Society
- 15, n.1
- pp.41-48
- 1982
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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.
1115
- 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.
1116
- 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.
1117
- Yun, Hong-Sik
- 天文學會誌 = The journal of the Korean Astronomical Society
- 15, n.1
- pp.37-39
- 1982
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High spatial and spectral resolution observations have been made over a sunspot (SPO 6403) with the Echelle Spectrograph at the Vacuum Tower Telescope, Sacramento Peak Observatory. Our observed spectra, scanned with SPO's fast microdensitometer, clearly show strengthening of <TEX>$C_2$</TEX> lines in the penumbra relative to the photosphere and much weakening in the umbra in agreement with the predictions made by our molecular equilibrium calculations (Lee et al. 1981).
1118
- Lee, See-Woo
- 天文學會誌 = The journal of the Korean Astronomical Society
- 15, n.1
- pp.19-36
- 1982
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For <TEX>${\sim}240$</TEX> nearby stars their age and mass were determined and kinematic parameters determined for 362 stars, applying Woolley's three-dimensional potential. Metallicity and kinematic parameters of these stars were correlated with their age, suggesting the slow collapse (<TEX>$t{\gtrsim}a$</TEX> few billion years) of the Galaxy and the initial rapid enrichment in metal abundance (<TEX>${\Delta}Z{\approx}1/3Z_1$</TEX>(present) for <TEX>${\sim}4{\times}10^8$</TEX> yrs). The late slow enrichment rate is given by <TEX>$d(Z/Z_{\odot})/dt=5.9{\sim}7.0{\pm}3.4$</TEX> per Gyr.
1119
- 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.
1120
- 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.