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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 70/122
691
- 박명구
- Journal of the Korean astronomical society = 천문학회지
- 34, n.2
- pp.81-97
- 2001
- 원문 바로보기
Since the first proposal by Paczynski, great efforts to detect Galactic dark matter by detecting light variations of stars located in the Magellanic Clouds and Galactic bulge caused by gravitational microlensing have been and are being carried out and more than 1,000 events have been successfully detected. In this paper, we review the progress in the theoretical and experimental progresses in microlensing. We begin with basics of microlensing and summarize the results obtained from the last 8 year observations along with the implications of the results. We also discuss the usefulness of microlensing in other fields of astronomy such as the stellar atmosphere, Galactic binary systems, and extra-solar planets. We finally discuss the problems of the current experiments and the new types of observations that can overcome these problems.
692
- GHOSH K. K.
- Journal of the Korean astronomical society = 천문학회지
- 34, n.1
- pp.9-15
- 2001
- 원문 바로보기
We present the results of optical differential photometry of five blazars [PKS0219+428 (3C66A), PKS 0235+164 (AO 0235+16), H0414+019, PKS 0851+202 (OJ 287) and QSO 1807+698 (3C 371)] that were observed on 7 nights between November 05, 1997 and December 29, 1998, using the B and the V band filters. We have detected microvariations in four blazars (3C66A, AO 0235+16, H04l4+019, and OJ 287). In addition, the light curve of AO 0235+16 has displayed a mini-flare when the brightness of this source was decreasing. Night-to-night variations have also been detected in 3C66A, H04l4+019, and OJ 287. The results of our observations are discussed in the framework of accretion disk phenomena (magnetic flares or hot spots in accretion disks) and jet phenomena (plasma instabilities in jets).
693
- SAAD SOMAYA MOHAMED
- Journal of the Korean astronomical society = 천문학회지
- 34, n.2
- pp.99-109
- 2001
- 원문 바로보기
In the present study we have determined the distance moduli for seven globular clusters M2, M3, Ml0, M12, NGC 2808, NGC 6229, and NGC 6752, whose metallicities are in the range -1.54 < [Fe/H] < -1.10. We have derived distances for them by the main-sequence fitting method using a sample of local subdwarfs, whose accurate parallaxes are taken from the Hipparcos Catalog. The derived distance moduli are 15.52 for M2, 14.98 for M3, 14.23 for Ml0, 14.03 for M12, 15.56 for NGC 2808, 17.34 for NGC 6229, and 13.29 for NGC 6752.
694
- OKUDA TORU
- Journal of the Korean astronomical society = 천문학회지
- 34, n.4
- pp.251-254
- 2001
- 원문 바로보기
To examine the structure and dynamics of thick accretion disks, we use a two-dimensional viscous hydrodynamic code coupled with radiation transport. The <TEX>$\alpha$</TEX>-model and the full viscous stress-tensor description for the kinematic viscosity are used. The radiation transport is treated in the gray, flux-limited diffusion approximation. The finite difference methods used are based on an explicit-implicit method. We apply the numerical code to the Super-Eddington black-hole model for SS 433.@The result for a very small viscosity parameter a reproduces well the characteristic features of SS 433, such as the relativistic jets with <TEX>$\~$</TEX>0.26c, the small collimation degree of the jets, the mass-outflow rate of <TEX>${\ge}5{\times}10^{-7}M{\bigodot}yr^{-1}$</TEX>, and the formation of the X-ray iron emission lines.
695
- CHOI CHUL-SUNG
- Journal of the Korean astronomical society = 천문학회지
- 34, n.3
- pp.129-135
- 2001
- 원문 바로보기
We report results from an analysis of the X-ray archival data on MCG-2-58-22 obtained with Ginga, ROSAT and ASCA. By analyzing both short- and long-term light curves, we find clear time variations, ranging widely from, <TEX>$\~10^3$</TEX> s to more than several years, in the X-ray energy range 0.1 - 10 keV. In addition, a flare is detected in 1991, overlaid on a gradual, secular flux decrease from 1979 to 1993; this flare has a time scale of about 1 year, and the X-ray flux increased by at least a factor of 3. The implications of these observational results are discussed in terms of accretion flow dynamics near a supermassive black hole.
696
- MIZUTA AKIRA
- Journal of the Korean astronomical society = 천문학회지
- 34, n.4
- pp.329-331
- 2001
- 원문 바로보기
We investigate the morphology of Active Galactic Nuclei(AGN) jets. AGN jets propagate over kpc <TEX>$\~$</TEX> Mpc and their beam velocities are close to the speed of light. The reason why many jets propagate over so long a distance and sustain a very collimated structure is not well understood. It is argued that some dimensionless parameters, the density and the pressure ratio of the jet beam and the ambient gas, the Mach number of the beam, and relative speed of the beam compared to the speed of light, are very useful to understand the morphology of jets namely, bow shocks, cocoons, nodes etc. The role of each parameters has been studied by numerical simulations. But more research is necessary to understand it systematically. We have developed 2D relativistic hydrodynamic code to analyze relativistic jets. We pay attention to the propagation velocity which is derived from 1D momentum balance in the frame of the working surface. We show some of our models and discuss the dependence of the morphology of jets on the parameter.
697
- KIM YONG HA
- Journal of the Korean astronomical society = 천문학회지
- 34, n.1
- pp.25-29
- 2001
- 원문 바로보기
We have constructed a non-spherical model for the hot oxygen corona of Mars by including the effects of planetary rotation and diurnal variation of the Martian ionosphere. Exospheric oxygen densities are calculated by integrating ensemble of ballistic and escaping oxygen atoms from the exobase over the entire planet. The hot oxygen atoms are produced by dissociative recombination of <TEX>$O^+_2$</TEX>, the major ion in the Martian ionosphere. The densities of hot oxygen atoms at the exobase are estimated from electron densities which have been measured to vary with solar zenith angle. Our model shows that the density difference of hot oxygen atoms between noon and terminator is about two orders of magnitude near the exobase, but reduces abruptly around altitudes of 2000 km due to lateral transport. The diurnal variation of hot oxygen densities remains significant up to the altitude of 10000 km. The diurnal variation of the hot oxygen corona should thus be considered when the upcoming Nozomi measurements are analyzed. The non-spherical model of the hot oxy-gen corona may contribute to building sophisticate solar wind interaction models and thus result in more accurate escaping rate of oxygens from Mars.
698
- JUNG JAE HOON
- Journal of the Korean astronomical society = 천문학회지
- 34, n.3
- pp.157-166
- 2001
- 원문 바로보기
The molecular cloud associated with the H II region S301 has been mapped in the J = 1-0 transitions of <TEX>$^{12}CO$</TEX> and <TEX>$^{13}CO$</TEX> using the 13.7 m radio telescope of Taeduk Radio Astronomy Observatory. The cloud is elongated along the north-south direction with two strong emission components facing the H II region. Its total mass is <TEX>$8.7 {\times} 10^3 M{\bigodot}$</TEX>. We find a velocity gradient of the molecular gas near the interface with the optical H II region, which may be a signature of interaction between the molecular cloud and the H II region. Spectra of CO, CS, and HCO+ exhibit line splitting even in the densest part of the cloud and suggests the clumpy structure. The radio continuum maps show that the ionzed gas is distributed with some asymmetry and the eastern part of the H II region is obscured by the molecular cloud. We propose that the S301 H II region is at the late stage of the champagne phase, but the second generation of stars has not yet been formed in the postshock layer.
699
- ISOBE HIROAKI
- Journal of the Korean astronomical society = 천문학회지
- 34, n.4
- pp.337-339
- 2001
- 원문 바로보기
One-dimensional hydrodynamic modeling of a protostellar flare loop is presented. The model consists of thermally isolated loop connecting the central core and the accretion disk. We found that the conductive heat flux of a flare heated the accretion disk up to coronal temperature and consequently the disk is evaporated and disappeard. This effect may explain the ovserved feature of the repeated flare from the young stellar object YLW 15.
700
- KYEONG JAE-MANN
- Journal of the Korean astronomical society = 천문학회지
- 34, n.3
- pp.143-147
- 2001
- 원문 바로보기
UBVI CCD photometry of open cluster NGC 2324 is presented. C-M diagrams of this cluster show well-defined main sequence with a red giant clump centered at B - V =1.05, V =13.45. We derived the major cluster characteristics; E(B - V)=0.17<TEX>$\pm$</TEX>0.12 from color-color diagram and mean color of red giant clump stars, (m - M)o=13.1<TEX>$\pm$</TEX>0.1 from zero age main sequence fitting, and [Fe/H]<TEX>$\~$</TEX>-0.32 from comparison the theoretical model developed by Bertelli et al. (1994) to the observed C-M diagrams. We estimate the age of NGC 2324 to be log t<TEX>$\~$</TEX>8.8 by applying isochrone fitting and morphological age index method.