모달창 닫기
- 홈으로 이동
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 78/122
771
- 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.
772
- 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>).
773
- 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.
774
- 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.
775
- 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.
776
- 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.
777
- 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.
778
- 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.
779
- KIM YONGCHEOL
- Journal of the Korean astronomical society = 천문학회지
- 31, n.2
- pp.77-87
- 1998
- 원문 바로보기
The accumulated knowledge of the influence of solar granulation on spectral lines, i.e. their asymmetry, provides a key to analyze stellar spectral line asymmetries. In this paper, a simple line synthesis using a simple 'model' of granulation was calculated. By adjusting the properties of the granule model, the observed imprints of convection on spectral lines can be reproduced. Since we depict convective flows using a continuous function rather than using a few components of flows (cf. Gray and Toner 1985, 1986; dravins 1990), we were able to identify which components of convection are important in line bisector shapes. The results of this study can be summarized as follows: Firstly, the intensity contrast (i.e. temperature fluctuation), and the area coverage of up- and down-flows are the two important factors which determine the line bisector shapes. Secondly, on the contrary to the assumption of other studies, the effect of horizontal flows is non-negligible. This exercise provides a qualitative understanding of the effect of convection on spectral lines. This knowledge serves as a guideline for understanding the characteristic difference in convection for stars on either side of the 'Granulation Boundary' (Gray 1982; Gray and Nagel 1989).
780
- PARK CHANGBOM
- Journal of the Korean astronomical society = 천문학회지
- 31, n.2
- pp.105-108
- 1998
- 원문 바로보기
We have found that the two-point correlation function of the APM clusters of galaxies has an amplitude much higher than that claimed by the APM group. As the richness limit increases from R = 53 to 80, the correlation length increases from 17.5 to 28.9 <TEX>$h^{-1}Mpc$</TEX>. This indicates that the richness dependence of the APM cluster correlation function is also much stronger than what the APM group has reported. The richness dependence can be represented by a fitting formula ro = 0.53dc + 0.01, which is consistent with the Bahcall's formula ro = 0.4dc. We have tried to find the possible reason for discrepancies. However, our estimates for the APM cluster correlation function are found to be robust against variation of the method of calculation and of sample definition.