Volume 2 Issue 2
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Nha, Il-Seong;Park, Hong-Suh;Kang, Young-Woon;Wood, Frank-Bradshaw;Williamon, Richard-M.;Leviton, Douglas-B. 69
The UBV observations of the Brightest RS CVn-type eclipsing binary star AR Lac were made at four observatories, two in Korean and two in the U.S. in the 1980-81 and 1981-82 seasons. As a result of the cooperation, two light curves in the yellow and in the blue were completed for each observing seasons. Ultraviolet observations were also made at three of the four observatories. The orbital period of AR Lac apparantly decreased around 1977. An analysis of our yellow light curves together with five other yellow curves available in the literature since 1975 shows that there seems no periodicity in the migration of the distortion waves. There is a gradual decrease of at least 0.m1 between 1976 and 1982 in the brightness of the cooler component if one assumes that the hotter component is constant. -
Using Brandt model the mess distribution of the late type spiral galaxy NGC 6946 was derived, and the total mass was reestimated to understand the M/L ratio of this galaxy. Two kinds of the rotation curve with shape parameter n=1 and 3.3 were examined. The following are the main results; (1) The total masses of NGC 6946 are
$3.1\times$ $10^{11}$ M(n=1) AND$2.8\times$ $10^{11}$ M(n=3.3) respectively. and the corresponding M/L are about 17 and 16 for both cases. (2) The optical image in the blue light, whose radius is 9.6 kpc, has 8$\times$ $10^{10}$ M and 1.4$\times$ $10^{11}$ M. These give the value of M/L about 5 and 8 respectively. (3) The masses and M/L of the nuclear region within 1.2 kpc are 4.0$\times$ $10^{9}$ M 4.7$\times$ $10^9$ M and 3, 4 for both cases. Those of the disk from 1.2 kpc to 9.6 kpc are 7.6$\times$ 1$10^{10}$ M, 1.4$\times$ $10^{11}$ M, and 5, 8. (4) The masses of the outer halo extended to few hundreds kiloparsecs are 2.3$\times$ $10^{11}$ M and 1.4$\times$ $10^{11}$ M. The corresponding M/L are about 62 and 37. -
Holmberg의 은하 직정과 SUGC에 있는 de Vaucouleurs face-on 은하 직경과의 차이는 BGC와 Holmberg 목록으로 Heidmann 등이 구한 차이보다 더 적게 나타났는데, 이는 펑균표면광도
$\mu_B$ = 24.5 등급에서 구한 face-on 은하 직경을 수록한 BGC 자료들을 H eidmann 등이 사용했기 때문이다. 또, 본 논문에서 구한 Holmberg 은하 직경과 de Vaucouleurs은하 직경과의 상관관계식에서$D_h>D_v$ 로 나타났으므로 Holmberg 은하 반청$b=\frac{1}{2}D_v$ 로 사용하는것이 옳지 않다고 본다. -
Fundamental data for 400 classical cepheids have been compiled. The PC-relation is derived and compared with similar relations for the Magellanic Clouds; it is fund that the differences are not great.
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The one of critical factor in gas turbine engine performance is high turbine inlet gas temperature. Therefore, the turbine rotor has so many problems which must be considered such as the turbine blade cooling, thermal stress of turbine disk due to severe temperature gradient, turbine rotor tip clearance, under the high operating temperature. The purpose of this study is to provider the temperature distribution and heat flux in turbine disk which is required to considered premensioned problem by the Finite Difference Method and the Finite Element Methods on the steady state condition. In this study, the optimum aspect ratio of turbine disk was analysed for various heat conductivity of turbine disk material by Finite Difference Method, and the effect of laminating method with high conductivity materials to disk thickness direction by Finite Element Methods in order to cool the disk. The laminating method with high conductivity material on the side of the disk is effective.