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1968년 ~ 2024년까지 1,201 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 : 1,201건 (DB Construction : 1,201 Articles)
총 게시글 1,201건
페이지 77/121
761
- 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.
762
- 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.
763
- 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.
764
- 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.
765
- CHOE G. S.
- Journal of the Korean astronomical society = 천문학회지
- 31, n.2
- pp.89-93
- 1998
- 원문 바로보기
An attempt is made to find the boundary tangential components of potential magnetic fields without constructing solutions in the entire domain. In our procedure, the magnetic energy is expressed as a functional of tangential and normal magnetic fields at the boundary and is minimized by the variational principle. This paper reports a preliminary study on two dimensional potential fields above a plane.
766
- LEE KANG HWAN
- Journal of the Korean astronomical society = 천문학회지
- 31, n.2
- pp.101-104
- 1998
- 원문 바로보기
We have obtained photometry of stars in NGC 2264 with several combinations of H<TEX>$\alpha$</TEX> filters and continuum filters. The main purpose of these observations was to determine the best filter combination for selecting low ma!,s member stars in their Pre-Main Sequence (PMS) stage using H<TEX>$\alpha$</TEX> photometry. A narrow band H<TEX>$\alpha$</TEX> filter (<TEX>${\Delta}{\lambda}$</TEX> = <TEX>$l0{\AA}$</TEX>) with any combination of continuum filters showed the highest resolution in the H<TEX>$\alpha$</TEX> photometry.
767
- 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.
768
- KIM MINSUN
- Journal of the Korean astronomical society = 천문학회지
- 31, n.2
- pp.109-115
- 1998
- 원문 바로보기
We show that the low density regions of the matter distribution preserve the properties of the primordial density field better than the high density regions. We have performed a cosmological N-body simulation of large-scale structure formation in the standard CDM cosmology, and studied the evolution of statistics of under-density and over-density regions separately. The rank-order of the under-density regions is closer to the original one compared to that of the over-density regions. The under-density peaks (or voids) has moved less than over-density peaks (or dense clusters of galaxies) from their initial positions. Therefore, the under-density regions are more useful than the over-density regions in the study of the statistical property of the primordial density field.
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
- KYEONG JAE-MANN
- Journal of the Korean astronomical society = 천문학회지
- 31, n.2
- pp.127-140
- 1998
- 원문 바로보기
With a large format near-infrared camera at the 2.2-m telescope on Mauna Kea Observatory, we performed J K near-infrared observations for the metal rich globular cluster NGC6712. This cluster lies near the galactic plane and therefore suffers heavy reddening. We present the near-infrared color-magnitude diagram and also derive the metallicity ([Fe/H] <TEX>${\~}-0.96{\pm}0.27$</TEX>) as well as its distance modulus ((m - M) <TEX>${\~}13.42{\pm}0.12$</TEX>).