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- The Korean Astronomical Society (The Korean Astronomical Society)
- 계간 (Quarterly)
- ISSN : 1225-4614 (ISSN : 1225-4614)
1225-4614
- DB구축현황 : 1,211건 (DB Construction : 1,211 Articles)
총 게시글 1,211건
페이지 77/122
761
- ANN H. B.
- Journal of the Korean astronomical society = 천문학회지
- 32, n.1
- pp.7-16
- 1999
- 원문 바로보기
Open clusters are useful tools to investigate the structure and evolution of the Galactic disk. We have started a long-term project to obtain UBVI CCD photometry of open clusters which were little studied before, using the Doyak 1.8 m telescope of Bohyunsan Optical Astronomy Observatory in Korea. The primary goals of this project are (1) to make a catalog of UBVI photometry of open clusters, (2) to make an atlas of open clusters, and (3) to survey and monitor variable stars in open clusters. Here we describe this project and report the first results based on preliminary analysis of the data on four open clusters in the survey sample: Be 14, Cr 74, Biu 9, and NGC 2355. Isochrone fitting of the color-magnitude diagrams of the clusters shows that all of them are intermediate age to old (0.3-1.6 Gyrs) open clusters with moderate metallicity.
762
- MOON YONG-JAE
- Journal of the Korean astronomical society = 천문학회지
- 32, n.1
- pp.65-73
- 1999
- 원문 바로보기
In this study we present a new improved nonlinear calibration method for vector magnetograms made by the Solar Flare Telescope of BOAO. To identify Fe I 6302.5 line, we have scanned monochromatic images of the line integrated over filter passband, changing the location of the central transmission wavelength of a Lyot filter. Then we obtained a filter-convolved line profile, which is in good agreement with spectral atlas data provided by the Sacramento Peak Solar Observatory. The line profile has been used to derive calibration coefficients of longitudinal and transverse fields, employing the conventional line slope method under the weak field approximation. Our improved nonlinear calibration method has also been used to calculate theoretical Stokes polarization signals with various angles of inclination of magnetic fields. For its numerical test, we have compared input magnetic fields with the calibrated ones, which have been derived from the new improved non-linear method and the conventional method respectively. The numerical test shows that the calibrated fields obtained from the improved method are consistent with the input fields, but not with those from the conventional method. Finally, we applied our new improved method to a dipole model which characterizes a typical field configuration of a single, round sunspot. It is noted that the conventional method remarkably underestimates the transverse field component near the inner penumbra.
763
- LEE JUNG-DEOK
- Journal of the Korean astronomical society = 천문학회지
- 32, n.2
- pp.91-107
- 1999
- 원문 바로보기
We present BVRI CCD photometry and near-infrared K photometry of the intermediate-aged open cluster NGC 7790. The reddening, E(B - V) = 0.54 <TEX>$\pm$</TEX> 0.05 and the distance modulus, (m - M)o = 12.45 <TEX>$\pm$</TEX> 0.10 for the cluster were determined by zero-age-main-sequence fitting and theoretical isochrone fitting using not only (V, B - V), (V, V - 1), (V, V - R) but also (V, V - K) color-magnitude diagrams. The reddening corresponded approximately to the average value derived from previous studies, while the distance modulus was found to be almost midway between the CCD photometric results of Romeo et al. (1989) and those of Mateo & Madore (1988). We have used four colors to distinguish members from field stars. The expected colors were calculated using the derived distance modulus, and were then were compared with the observed colors (B - V), (V - 1), (V - R), and (V - K). Thus, a color excess E(B - V) for each star was determined which could give the minimum difference between the calculated and observed colors. Single and binary members of the cluster were determined on the basis of the E(B - V) distribution of stars.
764
- CHAE JONGCHUL
- Journal of the Korean astronomical society = 천문학회지
- 32, n.2
- pp.137-147
- 1999
- 원문 바로보기
Recent studies show the importance of understanding three-dimensional magnetic reconnect ion on the solar surface. For this purpose, I consider non-coplanar magnetic reconnection, a simple case of three-dimensional reconnect ion driven by a collision of two straight flux tubes which are not on the same plane initially. The relative angle e between the two tubes characterizes such reconnection, and can be regarded as a measure of magnetic shear. The observable characteristics of non-coplanar reconnection are compared between the two cases of small and large angles. An important feature of the non-coplanar reconnect ion is that magnetic twist can be produced via the re-ordering of field lines. This is a consequence of the conversion of mutual helicity into self helicities by reconnection. It is shown that the principle of energy conservation when combined with the production of magnetic twist puts a low limit on the relative angle between two flux tubes for reconnect ion to occur. I provide several observations supporting the magnetic twist generation by reconnection, and discuss its physical implications for the origin of magnetic twist on the solar surface and the problem of coronal heating.
765
- MOON YONG-JAE
- Journal of the Korean astronomical society = 천문학회지
- 32, n.2
- pp.127-136
- 1999
- 원문 바로보기
In this study we present the study of solar active regions based on BOAO vector magnetograms and H<TEX>$\alpha$</TEX> filtergrams. With the new calibration method we analyzed BOAO vector magnetograms taken from the SOFT observational system to compare with those of other observing systems. In this study it has been demonstrated that (1) our longitudinal magnetogram matches very well the corresponding Mitaka's magnetogram to the extent that the maximum correlation yields r=0.962 between our re-scaled longitudinal magnetogram and the Mitaka's magnetogram; (2) according to a comparison of our magnetograms of AR 8422 with those taken at Mitaka solar observatory their longitudinal fields are very similar to each other while transverse fields are a little different possibly due to large noise level; (3) main features seen by our longitudinal magnetograms of AR 8422 and AR 8419 and the corresponding Kitt Peak magnetograms are very similar to each other; (4) time series of our vector magnetograms and H-alpha observations of AR 8419 during its flaring (M3.1/1B) activity show that the filament eruption followed the sheared inversion line of the quadrupolar configuration of sunspots, indicating that the flare should be associated with the quadrupolar field configuration and its interaction with new filament eruption. Finally, it may be concluded that the Solar Flare Telescope at BOAO works normally and it is ready to do numerous observational and theoretical works associated with solar activities such as flares.
766
- KIM YOUNG KWANG
- Journal of the Korean astronomical society = 천문학회지
- 32, n.1
- pp.17-39
- 1999
- 원문 바로보기
We investigate dynamical evolution of globular clusters with multi-mass component under the Galactic tidal field. We compare the results with our previous work which considered the cases of single-mass component m the globular clusters. We find the followings: 1) The general evolutions are similar to the cases of single-mass component. 2) There is no evidence for dependence on the orbital phase of the cluster as in the case of single-mass component. 3) The escape rate in multi-mass models is larger than that in the single-mass models. 4) The mass-function depends on radius more sensitively in anisotropic models than in isotropic models.
767
- LEE JEONG-EUN
- Journal of the Korean astronomical society = 천문학회지
- 32, n.1
- pp.41-53
- 1999
- 원문 바로보기
We have carried out high-resolution observations along one-dimensional cuts through the three Galactic super-shells GS 064-01-97, GS 090-28-17, and GS 174+02-64 in the HI 21 cm and CO J=l-0 lines. By comparing the HI data with IRAS data, we have derived the distributions of the <TEX>$I_{100}$</TEX> and <TEX>$T_{100}$</TEX> excesses, which are, respectively, the 100 <TEX>${\mu}m$</TEX> intensity and 100 <TEX>${\mu}m$</TEX> optical depth in excess of what would be expected from HI emission. We have found that both the <TEX>$I_{100}$</TEX> and <TEX>$T_{100}$</TEX> excesses have good correlations with the CO integrated intensity W co in all three supershells. But the <TEX>$I_{100}$</TEX> excess appears to underestimate <TEX>$H_2$</TEX> column density N(<TEX>$H_2$</TEX>) by factors of 1.5-3.8. This factor is the ratio of atomic to molecular infrared emissivities, and we show that it can be roughly determined from the HI and IRAS data. By comparing the <TEX>$T_{100}$</TEX> excess with <TEX>$W_{co}$</TEX>, we derive the conversion factor X <TEX>$\equiv$</TEX> N (<TEX>$H_2$</TEX>) /<TEX>$W_{co}{\simeq}$</TEX> 0.26 - 0.66 in the three supershells. In GS 090- 28-17, which is a very diffuse shell, our result suggests that the region with N(<TEX>$H_2$</TEX>) <TEX>$\le$</TEX> <TEX>$3 {\times} 10^{20} cm^{-2}$</TEX> does not have observable CO emission, which appears to be consistent with previous results indicating that diffuse molecular gas is not observable in CO. Our results show that the molecular gas has a 60/100 <TEX>${\mu}m$</TEX> color temperature <TEX>$T_d$</TEX> lower than the atomic gas. The low value of <TEX>$T_d$</TEX> might be due either to the low equilibrium temperature or to the lower abundance of small grains, or a combination of both.
768
- ANN HONG BAE
- Journal of the Korean astronomical society = 천문학회지
- 32, n.2
- pp.83-89
- 1999
- 원문 바로보기
We have conducted a V, I, J, and H surface photometry of a barred galaxy NGC 4314 to analyze the morphology and luminosity distribution of the galaxy. By applying a semi two-dimensional profile decomposition method, we derived the luminosity fractions and the scale lengths of the three distinct components, bulge, disk, and bar: <TEX>$L_b {\approx}0.35,\;L_d{\approx}0.35,\;L_{bar}{\approx}0.30,\;r_e{\approx}22',\;r_o {\approx} 50'$</TEX>, and a <TEX>$\approx$</TEX> 60'. The bulge of NGC 4314 seems to be triaxial due to the isophotal twists but its luminosity distribution is well approximated by the <TEX>$r^{1/4}$</TEX>-law.
769
- LEE HYUNG MOK
- Journal of the Korean astronomical society = 천문학회지
- 31, n.2
- pp.95-99
- 1998
- 원문 바로보기
We report preliminary results of an on-going survey of optically selected barred galaxies with <TEX>$^{12}CO$</TEX>(J=1-0) line. The entire sample is composed of about 100 bright barred galaxies (<TEX>$B_T{\le}13$</TEX>) with small inclination angle. Most of the galaxies are relatively nearby with receding speed less than 10,000 km/sec. In the first observing run, we have observed central parts of 18 galaxies and detected CO emissions from 5 galaxies (NGC521, 2525, 4262, 4900, and 7479). Most of these galaxies are not observed with CO previously, except for NGC7479 which has been studied at various wavelengths. The peak antenna temperature of detected galaxies ranges from about 30 to 300 mK.
770
- LEE KANG HWAN
- Journal of the Korean astronomical society = 천문학회지
- 31, n.1
- pp.19-26
- 1998
- 원문 바로보기
The wide field <TEX>$(\~20'\times20')$</TEX> CCD photometry has been performed for more than 4,000 stars over a whole region of NGC 362 which is located inside the SMC halo. The Color-Magnitude diagram (CMD) and luminosit function (LF) for red giant branch (RGB) stars are presented, discussing a distinct bump along the RGB and some blue stars appearing in the blue horizontal branch (BHB) and above BHB. The anomalous globular cluster NGC 362 with highly populated red horizontal branch (RHB) stars is compared with the another anomalous globular cluster NGC 288 with highly populated BHB stars. A metal-rich, young blue component and metal-'poor, old red component of the SMC halo stars are examined.