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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Journal of The Korean Astronomical Society
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The Korean Astronomical Society
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Volume & Issues
Volume 34, Issue 4 - Dec 2001
Volume 34, Issue 3 - Dec 2001
Volume 34, Issue 2 - Jun 2001
Volume 34, Issue 1 - Apr 2001
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ULTRAVIOLET ISOPHOTE SHAPES OF NEARBY ELLIPTICAL GALAXIES AND SPIRAL BULGES
SOHN YOUNG-JONG ;
Journal of The Korean Astronomical Society, volume 34, issue 2, 2001, Pages 59~66
In this paper, we investigate the correlation between the radial ultraviolet color distribution and the shapes of the ultraviolet isophote for elliptical galaxies (M32, NGC 1399) and spiral bulges (of M31, M81) by using their archival UIT images. For M31, M81, and NGC 1399, the radial ultraviolet color distributions show a two-component trend; as the distance from the galactic center increase the color becomes redder in the inner region while it becomes bluer in the outer region. On the other hand, the color of M32 continues to become bluer with the increasing galactocentric distance. We also find, unlike the optical/IR images, significant variations of the position angle and the ellipticity in the ultraviolet isophotes of M31, M81, and NGC 1399 through the inner regions. For M32, the variation is significant in the outer region. Since these variation implies the triaxiality of their intrinsic shapes, we suggest that the early-type galaxies and spiral bulges with a radial color gradient in ultraviolet tend to have a triaxiality. On the other hand, the shape parameter characterized by the fourth order cosine Fourier coefficient of the isophote, a(4)/a, indicates that the systematic deviations of the ultraviolet isophotes of the four galaxies are smaller than
in units of the semi-major axis. The latter result implies that the ultraviolet isophotes of the galaxies have a pure elliptical shape rather than the boxy or disky shapes. Therefore, there is no clear evidence of correlation between the radial ultra-violet color gradient and the boxy/disky shapes of isophotes.
CHEMICAL ABUNDANCE ANALYSIS OF M31 AND M33 BASED ON THE SPECTRUM OF HII REGIONS
HAN SOO RYEON ; HYUNG SIEK ; PARK HONG-SUH ; LEE WOO-BAlK ;
Journal of The Korean Astronomical Society, volume 34, issue 2, 2001, Pages 67~80
Chemical evolution of galaxies can be understood by studying the spatial distribution of heavy elements. We selected two nearby galaxies, M31 and M33 and investigated spectrum of their HII regions: a) the elec-tron densities have been derived from the [S II] 6717/6731 ratio along with the most recent atomic constants (Hyung & Aller 1996); b) the electron temperatures were determinated from the Pagel's empirical method. Nebula Model (Hyung 1994) has been employed to predict the spectral line intensities which gives the proper chemical abundances. The model would predict the line intensities correctly only when various input parameters such as the effective central star temperatures, gravity log g, model atmosphere as well as the geometry and the nebula physical condition are appropriate. Thus, the determination of chemical abundances of O, S, N of the two nearby galaxies M31 and M33 has been done, which shows a radial dependance of O/H and N/H: decrease with the distance, or increasing electron temperature due to the elemental deficiency. Abundances of M31 appear to be enhanced than those of M33.
Park Myeong-Gu ; Han Cheongho ;
Journal of The Korean Astronomical Society, volume 34, issue 2, 2001, Pages 81~97
Since the first proposal by Paczynski, great efforts to detect Galactic dark matter by detecting light variations of stars located in the Magellanic Clouds and Galactic bulge caused by gravitational microlensing have been and are being carried out and more than 1,000 events have been successfully detected. In this paper, we review the progress in the theoretical and experimental progresses in microlensing. We begin with basics of microlensing and summarize the results obtained from the last 8 year observations along with the implications of the results. We also discuss the usefulness of microlensing in other fields of astronomy such as the stellar atmosphere, Galactic binary systems, and extra-solar planets. We finally discuss the problems of the current experiments and the new types of observations that can overcome these problems.
DISTANCES OF GLOBULAR CLUSTERS BASED ON HIPPARCOS PARALLAXES OF NEARBY SUBDWARFS
SAAD SOMAYA MOHAMED ; LEE SANG-GAK ;
Journal of The Korean Astronomical Society, volume 34, issue 2, 2001, Pages 99~109
In the present study we have determined the distance moduli for seven globular clusters M2, M3, Ml0, M12, NGC 2808, NGC 6229, and NGC 6752, whose metallicities are in the range -1.54 < [Fe/H] < -1.10. We have derived distances for them by the main-sequence fitting method using a sample of local subdwarfs, whose accurate parallaxes are taken from the Hipparcos Catalog. The derived distance moduli are 15.52 for M2, 14.98 for M3, 14.23 for Ml0, 14.03 for M12, 15.56 for NGC 2808, 17.34 for NGC 6229, and 13.29 for NGC 6752.
NEW DIGITAL H
OBSERVATION BY SOLAR FLARE TELESCOPE AT BOAO
LEE C.-W. ; MOON Y.-J. ; PARK Y.D. ; JANG B.-H. ; KIM KAP-SUNG ;
Journal of The Korean Astronomical Society, volume 34, issue 2, 2001, Pages 111~117
Recently, we have set up a new digital CCD camera system, MicroMax YHS-1300 manufactured by Roper Scientific for Ha observation by Solar Flare Telescope at Bohyunsan Optical Astronomy Observatory. It has a 12 bit dynamic range, a pixel number of 1300
1030, a thermoelectric cooler, and an electric shutter. Its readout speed is about 3 frames per second and the dark current is about 0.05 e-/p/s at
. We have made a system performance test by confirming the system linearity, system gain, and system noise that its specification requires. We have also developed a data acquisition software which connects a digital camera con-troller to a PC and acquires H
images via Microsoft Visual C++ 6.0 under Windows 98. Comparisons of high quality H
images of AR 9169 and AR 9283 obtained from SOFT with the corresponding images from Learmonth Solar Observatory in Australia confirm that our H
digital observational system is performed properly. Finally, we present a set of H
images taken from a two ribbon flare occurred in AR 9283.
THE RELATIVE SUNSPOT NUMBERS IN 2000
SIM K. J. ; MOON Y.-J. ; LEE C.-W. ; CHANG B. H. ; WOO H. S. ;
Journal of The Korean Astronomical Society, volume 34, issue 2, 2001, Pages 119~127
We have analyzed 210 data of daily sunspot observations made during the period of January 3 to December 31 in 2000 and presented the daily relative sunspot numbers. For this work we estimated the conversion factors to derive the relative sunspot numbers: k=0.72 for the 20 cm refractor and k=0.56 for Solar Flare Telescope in KAO. During the year of 2000, our annual average of relative sunspot numbers is found to be 99.4. This number is obtained from the averaged daily number of 8.9 spot groups, in which there are about 62.5 distinct spots observed. According to the appearance of 423 spot groups, our analysis shows that the mean life time of the spot groups is about 4 day and 12.0 hours.