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1968년 ~ 2025년까지 1,227 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 : 1,227건 (DB Construction : 1,227 Articles)
총 게시글 1,227건
페이지 117/123
1161
- Hong, S.S.
- 天文學會誌 = The journal of the Korean Astronomical Society
- 14, n.1
- pp.37-42
- 1981
- 원문 바로보기
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.
1162
- Hyun, J.J.
- 天文學會誌 = The journal of the Korean Astronomical Society
- 14, n.2
- pp.51-54
- 1981
- 원문 바로보기
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.
1163
- Lee, S.W.
- 天文學會誌 = The journal of the Korean Astronomical Society
- 14, n.2
- pp.55-71
- 1981
- 원문 바로보기
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.
1164
- Chun, M.S.
- 天文學會誌 = The journal of the Korean Astronomical Society
- 14, n.1
- pp.13-17
- 1981
- 원문 바로보기
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.
1165
- 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.
1166
- Ann, H.B.
- 天文學會誌 = The journal of the Korean Astronomical Society
- 14, n.1
- pp.1-11
- 1981
- 원문 바로보기
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.
1167
- 우종옥
- 天文學會誌 = The journal of the Korean Astronomical Society
- 14, n.1
- pp.43-49
- 1981
- 원문 바로보기
Making use of log <TEX>$T_{eff}-M_{bol}$</TEX> diagram along with Stohers' stellar evolutionary tracks (1972), we estimated the masses of 107 O stars in HII regions, which were selected from the catalogue compiled by Goy (1973). It is found that our estimated masses of O stars range from <TEX>$20M_{\odot}\;to\;120M_{\odot}$</TEX> and about 20% of them falls in the mass range above <TEX>$60M_{\odot}$</TEX> in agreement with earlier findings of Conti et al. (1975).
1168
- Lee, H.M.
- 天文學會誌 = The journal of the Korean Astronomical Society
- 14, n.2
- pp.79-87
- 1981
- 원문 바로보기
Theoretical profiles of selected rotational lines of <TEX>$C_2$</TEX> CH, CN, TiO and MgH are computed by using the current models of sunspot unbrae and penumbrae. It is found that the lines of the diatomic carbides are enhanced in penumbrae relative to umbrae, while MgH lines are more strongly enhanced in umbrae than in penumbrae and the quiet photosphere. The results are discussed with respect to selecting lines suitable for studying the structure of sunspots.
1169
- Hong, Seung-Soo
- 天文學會誌 = The journal of the Korean Astronomical Society
- 13, n.1
- pp.35-44
- 1980
- 원문 바로보기
Various assumptions used in interpreting the observations of hydrogen recombination lines are critically assessed to confirm the gradient of electron temperature with distance from the galactic center. The total temperature increase from 5 to 13 kpc is about 2,500 K. Among many suggestions, we have singled out the decrease of trace dement abundances with the galactoccntric distance as the most viable cause for the temperature gradient. This will impose an important constraint on evolutionary models of the Galaxy.
1170
- Minn, Y.K.
- 天文學會誌 = The journal of the Korean Astronomical Society
- 13, n.1
- pp.9-14
- 1980
- 원문 바로보기
The abundances of simple molecules are examined in terms of the time-dependent cloud evolution. The formation and destruction mechanisms of <TEX>$H_2CO$</TEX> are reviewed. The average value of the fractional abundance of <TEX>$H_2CO$</TEX> is derived to be in the range of <TEX>$10^{-10}\;to\;5{\times}10^{-9}$</TEX>. This is comparable to the observed values. The expected variations of the molecules formed from or destroyed by CO, CI, and <TEX>$C^+$</TEX> whose abundances depend on the evolutionary state of the cloud are discussed.