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유계화,Yoo, Kye-Hwa 한국천문학회 2006 天文學論叢 Vol.21 No.2
We report a high resolution spectrum of AG Pegasi observed at Bohyunsan Optical Astronomy Observatory (BOAO) on October 2, 2004. Some of permitted emission lines, for example H I, He I, He II, Fe II and Ti II were observed in the spectrum of AG Pegasi in 2004. Lines presented in the longer wavelength region than $6500{\AA}$ are identified. And radial velocities for each element are measured. Then we carefully discuss the geometrical feature of AG Pegasi in October 2004.
상사해(相似解) 및 수치해를 이용한 점성원반 붕괴시 원반 구조 이해
유계화,Yoo, Kye-Hwa 한국천문학회 2005 天文學論叢 Vol.20 No.1
The problem for the collapse of isothermal and rotational self-gravitational viscous disk is considered. We derive self-similar solutions for the cases in the inner and outer regions of the self-gravitational viscous disk. We show that surface density depends on ${\sigma}_0/r$ in the outer region of the disk using a slow accretion approximation. The ratio of a modified viscous parameter in the outer region of the disk to that in the inner region is 0.042. We resorted to numerical solutions of governing equations of the self-gravitational disk to find out profiles of ${\sigma}$, u and ${\upsilon}$ in terms of x. Their profiles were rapidly changed around the innermost region of the self-gravitational disk. It indicates that a new object was formed in the most inner region of the disk.
유계화,Yoo, Kye-Hwa 한국천문학회 2005 天文學論叢 Vol.20 No.1
We present a high resolution spectrum of PU Vul observed at Bohyunsan Optical Astronomy Observatory (BOAO) on April 9, 2004. Permitted emission and nebular lines of PU Vul had been significantly changed compared to all spectra observed since its eruption in 1979. Therefore all new lines should be re-identified and were done so. We do-convoluted a $H{\beta}$ line into several emission components with Gaussian functions. Then we carefully discussed the geometrical feature of PU Vul in April 2004.
유계화,YOO KYE WHA 한국천문학회 2000 Journal of The Korean Astronomical Society Vol.33 No.3
The time-dependence of an $\alpha$-disk model under the influence of collisions of particles is examined. Collisions with viscosity tend to take away angular momentum. Both effects cause the disk to rotate more rapidly. The disk gradually contracts with increasing time.
유계화,YOO KYE WHA 한국천문학회 2001 Journal of The Korean Astronomical Society Vol.34 No.1
The collision effects in particles of the accretion disk are examined by the use of small perturbation. The collision force is assumed to be equal to 2 vV. From the equations governing collisions of such particles the local dispersion relation is obtained.
유계화,윤태석,강용희,Yoo, Kye-Hwa,Yoon, Tae-Seog,Kang, Yong-Hee 한국천문학회 2003 天文學論叢 Vol.18 No.1
The problem of the collapse of a self gravitating disk is here considered. We show self-similar solutions for the above problem under a modified viscous parameter. Surface density depends on r$^m$ in the inner region, where m is -1.6. Therefore growing central mass goes on without mass inflow to the system.
유계화,YOO KYE HWA 한국천문학회 2002 天文學論叢 Vol.17 No.1
Our examination of the relations of spherically symmetric accretion on a massive point object to viscous drag, neglecting gas pressure and using self-similar transformation, shows the behaviors of the asymptotic solutions? in the regions near to and far from the center. The viscosity reduces the free-fall velocity by the factor $(1\;+\;\zeta) ^{-1}$, and causes flattening in the density distribution. Therefore, the viscosity leads to the reduction of the mass accretion rate.
柳桂和 梨花女子大學校 韓國生活科學硏究院 1989 韓國生活科學硏究院 論叢 Vol.44 No.-
1967년, 1977년의 CH Cygni의 폭발현상 때, Balmer선의 변화에 대하여 서술했다. Balmer선의 lower members의 선폭증가는 Stark효과에는 무관하나, 작은 양이지만 난류운동에는 관계가 있는 것 같다. 선폭증가의 주원인은 강착원반에서의 물질의 Kepler운동에 의한 Doppler효과 때문으로 생각된다. 폭발현상 때의 복사는 M6Ⅲ와 어떤 black body의 복합복사를 나타낸다. The Spectral behaviours of the Balmer lines during the eruption phases in 1967, and 1977 were described. It seemed to show that the line broadening of the lower members in the Balmer lines was not due to the Stark effect, but due to the small turbulence motion in the disk. The most line broadening results from the Doppler effect brought by the Keplerian motion of the matter in the disk. The composite radiation in both MbⅢ and a black body required the radiation of the CH Cygni in these active periods.