모달창 닫기
- 홈으로 이동
1968년 ~ 2023년까지 1,187 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 : 1,187건 (DB Construction : 1,187 Articles)
총 게시글 1,187건
페이지 75/119
741
- 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.
742
- 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.
743
- 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.
744
- 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.
745
- 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.
746
- 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.
747
- LEE DONG WOOK
- Journal of the Korean astronomical society = 천문학회지
- 31, n.1
- pp.27-37
- 1998
- 원문 바로보기
We have made semi-analytical studies to investigate the configurations of caustics and the probability distribution of the flux factor K for the binary microlensing including external shears. A parametric equation of critical curve is derived in a 4th order complex polynomial. We present the topological dependencies of the caustics for selected gamma parameters (0, 0.3, 0.6, 1.3, 2.0, and 2.5) and convergence terms (0., 0.4, 0.8, 1.2, 1.6, and 2.0). For the purpose of analyzing the efficiency of High Amplification Event (HAE) on each caustics, we examine the probability distribution of the flux factor by a Monte Carlo method. Changing the separation of the binary system from 0.8 to 1.3 (in normalied unit), we examine the probability distribution of the K-values in various gamma parameters. The relationship between gamma parameters, seperations and their probabilties of the flux factor K have been studied. Our results show that the relatively higher K values (K>1.5) are increased as increasing the separation of the binary system. We therfore conclude that, in the N-body microlensing, the probabilities of higher HAEs are inversely proportional to the star density as well. We also point out that the present research might be used as a preliminary step toward investigating heavy N-body microlensing simulations.
748
- ANN HONG BAE
- Journal of the Korean astronomical society = 천문학회지
- 31, n.1
- pp.39-50
- 1998
- 원문 바로보기
We present UBV CCD photometry of Be 2, previously unstudied open cluster. Our photometry covers a field of <TEX>$3'.2\times3'.8$</TEX> of the sky centered on the cluster, which is slightly smaller than the cluster diameter estimated to be about 260'. We have determined the reddening, distance, age and metallicity of the cluster by fitting the Pad ova isochrones to the observed stellar distributions in color-magnitude diagram as well as main sequence fitting: <TEX>$E(B-V)=0.8\pm0.05,\;(m-M)_o=13.6\pm0.1,\;log(t) =8.9\pm0.1$</TEX>, and Z=0.008. The present photometry shows that Be 2 is a distant open cluster of intermediate age. that it is a distant intermediate-age open duster.
749
- YUN HONG SIK
- Journal of the Korean astronomical society = 천문학회지
- 31, n.1
- pp.1-17
- 1998
- 원문 바로보기
To understand the basic physics underlying large spatial fluctuations of intensity and Doppler shift, we have investigated the dynamical charctersitics of the transition region of the quiet sun by analyzing a raster scan of high resolution UV spectral band containing H Lyman lines and a S VI line. The spectra were taken from a quiet area of <TEX>$100'\times100'$</TEX> located near the disk center by SUMER on board SOHO. The spectral band ranges from 906 A to 950 A with spatial and spectral resolution of 1v and <TEX>$0.044 {\AA}$</TEX>, respectively. The parameters of individual spectral lines were determined from a single Gaussian fit to each spectral line. Then, spatial correlation analyses have been made among the line parameters. Important findings emerged from the present analysis are as follows. (1) The integrated intensity maps of the observed area of H I 931 line <TEX>$(1\times10^4 K)$</TEX> and S VI 933 line <TEX>$(2\times10^5 K)$</TEX> look very smilar to each other with the same characterstic size of 5'. An important difference, however, is that the intensity ratio of brighter network regions to darker cell regions is much larger in S VI 933 line than that in H I 931 line. (2) Dynamical features represented by Doppler shifts and line widths are smaller than those features seen in intensity maps. The features are found to be changing rapidly with time within a time scale shorter than the integration time, 110 seconds, while the intensity structure remains nearly unchanged during the same time interval. (3) The line intensity of S VI is quite strongly correlated with that of H I lines, but the Doppler shift correlation between the two lines is not as strong as the intensity correlation. The correlation length of the intensity structure is found to be about 5.7' (4100 km), which is at least 3 times larger than that of the velocity structure. These findings support the notion that the basic unit of the transition region of the quiet sun is a loop-like structure with a size of a few <TEX>$10^3 km$</TEX>, within which a number of unresolved smaller velocity structures are present.
750
- RYU OK-KYUNGI
- Journal of the Korean astronomical society = 천문학회지
- 31, n.2
- pp.161-171
- 1998
- 원문 바로보기
We have mapped about 1.5 square degree regions of Lynds 1299, a well isolated dark cloud in the Outer Galaxy (l = <TEX>$122^{\circ}$</TEX>, b = <TEX>$-7^{\circ}$</TEX>), in the J = 1- 0 transition of <TEX>$^{12}CO$</TEX> and <TEX>$^{13}CO$</TEX> with the 13.7 m radio telescope at Taeduk Radio Astronomy Observatory (TRAO). We found that there are two velocity components in the molecular emission, at <TEX>$V_{LSR} = -52 km S^{-1}$</TEX> (Cloud A) and -8.8 km <TEX>$s^{-1}$</TEX> (Cloud B), respectively. We have derived physical parameters of two molecular clouds and discussed three different mass estimate techniques. We found that there are large discrepancies between the virial and LTE mass estimates for both clouds. The large virial mass estimate reflects the fact that both are not gravitationally bound. We adopt the mass of <TEX>$5.6 {\times}10^3 \;M{\bigodot}$</TEX> for Cloud A and <TEX>$1.2{\times}10^3 \;M{\bigodot}$</TEX>) for Cloud B using conversion factor. Cloud A is found to be associated with a localized star forming site, and its morphology is well matching with that of far-infrared (FIR) dust emission. It shows a clear ring structure with an obvious velocity gradient. We suggest that it may be a remnant cloud from a past episode of massive star formation. Cloud B is found to be unrelated to Cloud A (d = 800 pc) and has no specific velocity structure. The average dust color temperature of the uncontaminated portion of Cloud A is estimated to be 24<TEX>$\~$</TEX>27.4 K. The low dust temperature may imply that there is no additional internal heating source within the cloud. The heating of the cloud is probably dominated by the interstellar radiation field except the region directly associated with the new-born B5 star. Overall, the dust properties of Cloud A are similar to those of normal dark cloud even though it does have star forming activity.