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1968년 ~ 2024년까지 1,211 건의 한국천문학회지를 격월간 확인하실 수 있습니다.
- 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 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.
762
- 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.
763
- SUNG HWANKYUNG
- Journal of the Korean astronomical society = 천문학회지
- 32, n.2
- pp.109-117
- 1999
- 원문 바로보기
UBVI CCD photometry has been obtained for a region around the Wolf-Rayet star WR 12. We found two young stellar associations in the observed field: the nearer one comprises the field members of Vela OBI association at d = 1.8kpc, while the farther one is the young open cluster Bochum 7 (Bo 7) at d = 4.8kpc. The stars associated with Bo 7 showed no central concentration which suggests that Bo 7 is not a young open cluster but simply a local concentration in the density of young stars belonging to the OB association (Vel OB3). These two associations have similar ages but remarkably different mass function slopes (<TEX>$\Gamma$</TEX> = -2.1 <TEX>$\pm$</TEX> 0.3 for Vel OBI and -1.0 <TEX>$\pm$</TEX> 0.3 for Bo 7). The stars in Vel OBI shows an evident age spread (<TEX>${\Delta}T\~ 9Myr$</TEX>). We also found two strong H<TEX>$\alpha$</TEX> emission stars - WR 12 and <TEX>$\sharp$</TEX>1066 - from narrow band H<TEX>$\alpha$</TEX> photometry.
764
- ANN HONG BAE
- Journal of the Korean astronomical society = 천문학회지
- 32, n.1
- pp.1-6
- 1999
- 원문 바로보기
We have conducted near-infrared (J- and H-band) surface photometry for two early type barred galaxies, NGC 3412 and NGC 3941. The bulges of NGC 3412 and NGC 3941 show isophotal twists which indicate that they are triaxial. NGC 3412 has a very short bar and its bulge is more centrally concentrated than that of NGC 3941. The unusually short bar and the centrally concentrated triaxial bulge of NGC 3412 might be the result of bar dissolution. The colors of the nuclear region of NGC 3941 resemble those of the blue nuclei, implying the presence of young stellar populations.
765
- 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.
766
- 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.
767
- 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.
768
- 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.
769
- CHOI YOUNG-JUN
- Journal of the Korean astronomical society = 천문학회지
- 31, n.2
- pp.141-160
- 1998
- 원문 바로보기
We have conducted BV RI CCD surface photometry of three spiral galaxies ESO 598-G009, NGC 1515 and NGC 7456. In order to understand the morphological properties and luminosity distribution characteristics for each galaxy, we derived isophotal map, position angle profile, ellipticity profile, luminosity profile, color profile and color contour map. ESO 598-G009, which has a bright bulge component and a ring, shows a trace of gravitational interaction. NGC 1515 is a spiral galaxy with a bar and dust lane. NGC 7456 shows typical characteristics of a late type spiral galaxy.
770
- MINH Y. C.
- Journal of the Korean astronomical society = 천문학회지
- 31, n.2
- pp.117-125
- 1998
- 원문 바로보기
We have observed the 10-9 transitions of <TEX>$HC_3N$</TEX> and its <TEX>$^{13}C$</TEX> substitutes (<TEX>$H^{13}CCCN,\;HC^{13}CCN$</TEX>, and <TEX>$HCC^{13}CN$</TEX>), and the vibration ally excited 12-11 (<TEX>$v_r=1$</TEX>) <TEX>$HC_3N$</TEX> transition toward the Sgr B2 molecular cloud. The observed <TEX>$HC_3N$</TEX> emission shows an elongated shape around the Principal Cloud (<TEX>$\~$</TEX>4.5 pc in R.A. <TEX>$\times$</TEX> 7.4 pc in Decl.). The optically thin <TEX>$H^{13}CCCN$</TEX> line peaks around the (N) core and we derive the total column density <TEX>$N(H^{13}CCCN) = 4 {\times}10^{13} cm^{-2}$</TEX> at this position. Toward the 2' N cloud which shows the peculiar chemistry, the <TEX>$HC_3N$</TEX> lines show enhancements compared to the extended envelope. The shocks of the 2' N may have resulted in the enhancement of <TEX>$HC_3N$</TEX>. The hot component of <TEX>$HC_3N$</TEX> is strongly concentrated around the (N) core and its HPW is <TEX>$\~$</TEX>0.9 pc in diameter. We derive the lower limit of the abundance ratio <TEX>$N(HC_3N)/N(H^{13}CCCN)$</TEX> to be larger than 40 in most regions except the (M) and (N) cores. The fractionation processes of <TEX>$^{13}C $</TEX>at this region may not be as effective as previously reported.