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- 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
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1071
- Sohn, Young-Jong
- 天文學會誌 = The journal of the Korean Astronomical Society
- 24, n.2
- pp.151-159
- 1991
- 원문 바로보기
Using the photographic imagery of the SO galaxy NGC 5102, the equivalent luminosity profile and the fractional integrated luminosity curve have been derived. Several photometric parameters of the galaxy, such as a total magnitude (<TEX>$B_T$</TEX>), equivalent radius (<TEX>$r^*_e$</TEX>), effective surface brightness (<TEX>${\mu}^*_e$</TEX>), and concentration indices (<TEX>$C_{21}$</TEX>, <TEX>$C_{32}$</TEX>) were derived from the luminosity profiles. According to the decomposition method from the nonlinear least squares fitting, photometric parameters of the bulge (<TEX>${\mu}_e$</TEX>, <TEX>$r_e$</TEX>) and the exponential disk (<TEX>${\mu}(0)$</TEX>, <TEX>${\alpha}^{-1}$</TEX>), and the bulge to total luminosity ratio (B/T) were obtained. The derived central disk surface brightness (<TEX>${\mu} (0)\;=\;22.06\;{\pm}\;0.18\;mag/\Box'$</TEX>) and the evaluated B/T ratio (= 0.52) of the NGC 5102 are close to the mean values (<TEX>${\mu} (0)\;=\;21.65\;{\pm}\;0.3\;mag/\Box'$</TEX>, B/T=0.63) of the SO galaxies. Analysis showed that a lens-like hump is embedded in the equivalent luminosity profile of the NGC 5102.
1072
- Kim, K.T.
- 天文學會誌 = The journal of the Korean Astronomical Society
- 24, n.1
- pp.95-105
- 1991
- 원문 바로보기
In the presence of synchrotron losses, diffusion of an ensembel of relativistic particles in an intraculster medium is investigated. The diffusion coefficient in the medium is found to be constrained by <TEX>$28.8\;{\pm}\;0.4\;{\leq}\;Log\;D\;{\leq}\;30.5\;{\pm}\;0.4\;cm^2s^{-1}$</TEX> with the energy dependency of <TEX>$D_0{\varepsilon}^{\mu}$</TEX> of <TEX>${\mu}=0.4{\pm}0.2$</TEX> as the previous observations suggested. As an important implication of the result, the brightest head-tail radio source NGC 4869, whose radio tail structure is indicative for its orbit within the cluster core, is considered to be the major contributor of particles for the formation of the Coma radio halo.
1073
- Ann, Hong-Bae
- 天文學會誌 = The journal of the Korean Astronomical Society
- 24, n.1
- pp.13-24
- 1991
- 원문 바로보기
We construct a simple photometric evolution model of galaxies based on the evolutionary population synthesis. In our models an exponentially decreasing SFR with a power law IMF is used to compute the UBV colors of galaxies from ellipticals to late type spirals. It is shown that the integrated colors of galaxies with different Hubble type can be explained by one parameter, SFR.
1074
- Lee, H.M.
- 天文學會誌 = The journal of the Korean Astronomical Society
- 24, n.1
- pp.55-70
- 1991
- 원문 바로보기
Infrared emission maps are constructed at 12.5, 25, 60, and <TEX>$100{\mu}m$</TEX> for dark globules B5, B34, B133, B134, B361, L134 and L1523 by using Infrared Astronomical Satellite data base. These clouds are selected on the basis of their appearance in Palomar print as dark obscuring objects with angular sizes in the range of 3 to 30 arcminutes. The short wavelength(12.5 and <TEX>$25{\mu}m$</TEX>) maps show the embedded infrared sources. We found many such sources only in B5, B361 and B34 regions, Diffuse component at 12.5 and <TEX>$25{\mu}m$</TEX>, possibly arising from the stochastically heated very small dust grains(a < <TEX>$0.01{\mu}m$</TEX>) by interstellar radiation field, is found in B361 and L1523 regions. Such emission is characterized by the limb brightening, and it is confirmed in L1523 and in B361. Infrared emissions at the long wavelengths(60 and <TEX>$100{\mu}m$</TEX>) are due to colder dusts with temperature less than 20 K. The distribution of color index determined by the ratio 60 to <TEX>$100{\mu}m$</TEX> intensities shows monotonic decrease of dust temperature toward the center. The black body temperature determined from these ratios is found to lie between 16 and 23 K. Such temperature is possible for small(i.e., <TEX>$a\;{\lesssim}\;0.01{\mu}m$</TEX>) graphite grains if the grains are mainly heated by interstellar radiation field. Thus IRAS 100 and <TEX>$60{\mu}m$</TEX> emissions are arising mainly from small grains in the colud. The distribution of such dust grains implied from the emissivity distributions at 100 and <TEX>$60{\mu}m$</TEX> resembles that of isothermal sphere. This contrasts to earlier findings of much steeper distribution of dusts contributing visible extinction. These dust grains are mainly larger ones(i.e., <TEX>$a{\simeq}0.1{\mu}m$</TEX>). Therefore we conclude that the average grain size increase, toward the cloud center.
1075
- Hong, S.S.
- 天文學會誌 = The journal of the Korean Astronomical Society
- 24, n.1
- pp.71-94
- 1991
- 원문 바로보기
With the 14 m radio telescope at DRAO and the 4 m at Nagoya University, we have made detailed maps of <TEX>$^{12}CO$</TEX> and <TEX>$^{13}CO$</TEX> emissions from two Barnard objects B133 and B134 in the <TEX>$J=1{\rightarrow}O$</TEX> rotational transition lines. Usual LTE analyses of the CO observations led us to determine the distribution of column densities over an entire area encompassing both globules. Total gas masses estimated from the column density map are <TEX>$90\;M_{\odot}$</TEX> and <TEX>$20\;M_{\odot}$</TEX> for B133 and B134, respectively. The radial velocity of B133 is red shifted with respect to B134 by <TEX>$0.8\;km\;s^{-1}$</TEX>, which is too lagre to bind the two clouds as a binary system. We have shown that the usual stability analysis based on the simplified version of virial theorem with the second time-derivative of the moment of inertia term <TEX>$\ddot{I}$</TEX> being ignored could mislead us in determining whether a given cloud eventually collapses or not. The lull version of the scalar virial theorem with the <TEX>$\ddot{I}$</TEX> term is shown to be useful in following up the time-dependent variations of the cloud size R and its streaming velocity <TEX>$\dot{R}$</TEX> as functions of time. Results of our stability analysis suggest that B133 will eventually collapse in <TEX>$(2{\sim}4){\times}10^6$</TEX> years.
1076
- Kim, Mee-Jeong
- 天文學會誌 = The journal of the Korean Astronomical Society
- 24, n.2
- pp.173-190
- 1991
- 원문 바로보기
Disk stellar luminosity function has been derived with stars in the Lowell Proper Motion Survey which contains about 9000 stars with <TEX>${\mu}\;{\geq}\;0'.27$</TEX> of arc/yr, <TEX>$8\;</TEX><TEX><</TEX><TEX>\;m_{pg}\;</TEX><TEX><</TEX><TEX>\;17$</TEX> and with bright stars in the Smithsonian Astrophysical Observatory (SAO) Star Catalogue, Luminosity function has been obtained with stars within 20 pc by Luyten's mean absolute magnitudes method using Reduced Proper Motion Diagram to select disk stars. Magnitudes and colors, in the SAO Star Catalogue as well as in the Lowell Proper Motion Survey have been transformed to the UBV system from the published UBV data. It has been found that stars which have higher proper motion than the original limit of the proper motion survey are missed, when the relation between the absolute magnitude and reduced proper motion is applied to sample stars without considering the dispersion in magnitude. Correction factors for missing stars have been estimated according to their limits of proper motion which are dependent on the absolute magnitude. Resulting luminosity function shows Wielen's dip at <TEX>$M_B{\sim}10$</TEX>, and systematic enhancement of stars on the average of about <TEX>${\Delta}\log\;{\Phi}\;(M_B){\sim}0.2$</TEX> compared with Luyten's luminosity function.
1077
- Moon, Yong-Jae
- 天文學會誌 = The journal of the Korean Astronomical Society
- 24, n.2
- pp.129-149
- 1991
- 원문 바로보기
An attempt has been made to examine the characteristics of acoustic and MHD waves generated in stellar convection zones(<TEX>$4000\;K\;{\leq}\;T_{eff}\;{\leq}\;7000\;K$</TEX>, <TEX>$3\;{\leq}\;\log\;g\;{\leq}\;4.5$</TEX>). With the use of wave generation theories formulated for acoustic waves by Stein (1967), for MHD body waves by Musielak and Rosner (1987, 1988) and for MHD tube waves by Musielak et al.(l989a, 1989b), the energy fluxes are calculated and their dependence on effective temperature, surface gravity and megnetic field strength are analyzed by optimization techniques. In computing magneto-convection models, the effect of magnetic fields on the efficiency of convection has been taking into account by extrapolating it from Yun's sunspot models(1968; 1970). Our study shows that acoustic wave fluxes are dominant in F and G stars, while the MHD waves dominant in K and M stars, and that the MHD wave fluxes vary as <TEX>$T_{eff}^4{\sim}T_{eff}^7$</TEX> in contrast to the acoustic fluxes, as <TEX>$T_{eff}^{10}$</TEX>. The gravity dependence, on the other hand, is found to be relatively weak; the acoustic wave fluxes <TEX>${\varpropto}\;g^{-0.5}$</TEX>, the longitudinal tube wave fluxes <TEX>${\varpropto}\;g^{0.3}$</TEX> and the transverse tube wave fluxes <TEX>${\varpropto}\;g^{0.3}$</TEX>. In the case of the MHD body waves their gravity dependence is found to be nearly negligible. Finally we assesed the computed energy fluxes by comparing them with the observed fluxes <TEX>$F_{ob}$</TEX> of CIV(<TEX>${\lambda}1549$</TEX>) lines and soft X-rays for selected main sequence stars. When we scaled the corrected wave fluxes down to <TEX>$F_{ob}$</TEX>, it is found that these slopes are almost in line with each other.
1078
- Minn, Y.K.
- 天文學會誌 = The journal of the Korean Astronomical Society
- 24, n.2
- pp.191-215
- 1991
- 원문 바로보기
We have compared the column densities of <TEX>$H_2CO$</TEX>, <TEX>$^{13}CO$</TEX>, <TEX>$C^{18}O$</TEX>, <TEX>$^{12}CO$</TEX>, CS, and <TEX>$HCO^+$</TEX> to the visual extinctions derived from star counts in eight dark clouds, L1317, B1, L1551, L1535, L1544, L134, L134N, and B335. We examined the degree of correlation between molecules and extinctions. The contours of <TEX>$^{13}CO$</TEX>, <TEX>$H_2CO$</TEX>, and CS distributions show an excellent coincidence with those of the visual extinction. Even though the plots of molecule brightness temperature or column density as a function of the visual extinction show a considerable scatter, a good correlation is found between the two quantities. The turnover of the ratios of <TEX>$^{13}CO$</TEX> and <TEX>$H_2CO$</TEX> column densities to the visual extinction at high extinctions observed in several clouds is not apparent in this work. The ratios seem to maintain constant values within the range of <TEX>$A_V$</TEX> we studied. The slopes of the relations between the molecule column density and extinction, and the threshold values of extinction for detection of molecules are comparable to the other works. The cause of the slope difference is discussed. We derived, for the first time, the relations of CS and <TEX>$HCO^+$</TEX> column densities and the visual extinction. The ratio of CS column density to extinction is at least two orders of magnitude lower than the mean value for <TEX>$^{13}CO$</TEX>, but the threshold for detection of CS is comparable to that of <TEX>$^{13}CO$</TEX>. The ratio of the <TEX>$HCO^+$</TEX> column density to extinction is one to two orders of magnitude lower than the mean ratio for <TEX>$H_2CO$</TEX>.
1079
- Chang, Kyong-Ae
- 天文學會誌 = The journal of the Korean Astronomical Society
- 24, n.1
- pp.1-12
- 1991
- 원문 바로보기
The mathematical properties of gravitational lens equations are examined in the frame work of gravitational micro-lensing effects. The caustics of the gravitational lens may be defined in terms of 'cusp' and 'folding' in general. In some cases for overfocussing, however, the critical curves (caustics) have no cusp and no folding. If the observer is in the overfocussed region, he may not see any lensed image.
1080
- Chung, H.S.
- 天文學會誌 = The journal of the Korean Astronomical Society
- 24, n.2
- pp.217-271
- 1991
- 원문 바로보기
We have observed dense core around young stellar objects, DR21, S140, Orion-KL, and L1551 using four millimeter-wave transitions of <TEX>$HC_3N\;J$</TEX>=4-3, J=5-4, J=10-9, and J=12-11. The spatial distribution of <TEX>$HC_3N$</TEX> emission closely resembles the morphology of the previous CS observations that trace high density gas. These observations reveal the existence of <TEX>$HC_3N$</TEX> dense cores around central IR source, elliptical in shape and almost perpendicular to the CO bipolar outflow axis. Small differences can be explained by that <TEX>$HC_3N$</TEX> molecular line is more optically thin and is seen to be more detailed structure in the neighborhood of central IR sources. In S140 and Orion-KL, massive(<TEX>${\sim}10\;M_{\odot}$</TEX>), slowly rotating dense cores lie near at the central IR sources of bipolar outflows. The velocity channel maps of DR21 show that the bipolar outflow gas may have a correlation with the dense core of DR21. We analyzed intensities of the four lines to derive physical conditions in dense core from two methods, LTE and LVG. The column density of <TEX>$HC_3N$</TEX>, <TEX>$N(HC_3N)$</TEX>, between LTE and LVG calculations agree well with each other. The abundances of <TEX>$HC_3N$</TEX> in each observing source have been estimated using the average values of <TEX>$n(H_2)$</TEX> and <TEX>$N(HC_3N)$</TEX> and assuming the size of dense core. The fractional <TEX>$HC_3N$</TEX> abundances in massive dense cores of DR21, S140, and Orion-KL have a range of <TEX>$(2-7){\times}10^{-10}$</TEX>, while that of low mass dense core, L1551, has one order of magnitude greater value of <TEX>$2{\times}10^{-9}$</TEX>. This should be considered good agreement with the result by Morris et al.(1976). It may be considered that dense cores of DR21, S140, and Orion-KL may have almost same stage of chemical evolution, and their abundances have a small values relative to that of L1551. The column density <TEX>$N(HC_3N)$</TEX> decreases with increasing distance from the densest part of the cloud, the central infrared source, and have the relation of <TEX>$N(HC_3N){\varpropto}R^{\alpha}$</TEX>, where a has a range of 0.65 to 0.89. The values of <TEX>$n(H_2)$</TEX> are not varied with increasing distance from the dense core, and have almost same values. Therefore, it is considered that the dense cores in these regions probably consist of dense clumps in diffuse molecular gas medium, and <TEX>$n(H_2)$</TEX> of each clump is <TEX>${\sim}10^5\;cm^{-3}$</TEX>. Levels in the <TEX>$T_{ex}$</TEX> increases with <TEX>$n(H_2)$</TEX>. It is considered that the <TEX>$HC_3N$</TEX> dense cores are not completely thermalized. We examine the relationships between the luminosity of central infrared sources versus mass of the dense cores, and the luminosity of central infrared sources versus molecular hydrogen column density. Luminosities of the central IR sources show good correlation with mass and hydrogen column density of the dense core. Same has been found from CS observations. However, mass and size derived from <TEX>$HC_3N$</TEX> observations are one order of magnitude smaller than those from CS. It can be interpreted that we see more central part of the cloud cores in <TEX>$NC_3N$</TEX> lines than CS lines.