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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 72/122
711
- JONES T. W.
- Journal of the Korean astronomical society = 천문학회지
- 34, n.4
- pp.225-230
- 2001
- 원문 바로보기
Rarefied cosmic plasmas generally do not achieve thermodynamic equilibria, and a natural consequence of this is the presence of a significant population of charged particles with energies well above those of the bulk population. These are exemplified by the galactic cosmic rays, but the importance of these high energy populations extends well beyond that context. I review here some of the basic issues associated with the propagation and acceleration of cosmic rays, especially in the context of collisionless plasma shocks.
712
- TANUMA SYUNITI
- Journal of the Korean astronomical society = 천문학회지
- 34, n.4
- pp.309-311
- 2001
- 원문 바로보기
Strong thermal X-ray emission, called Galactic Ridge X-ray Emission, is observed along the Galactic plane (Koyama et al. 1986). The origin of hot (<TEX>$\~$</TEX>7 keV) component of GRXE is not known, while cool (<TEX>$\~$</TEX>0.8 keV) one is associated with supernovae (Kaneda et al. 1997, Sugizaki et al. 2001). We propose a possible mechanism to explain the origin; locally strong magnetic fields of <TEX>$B_{local}\;\~30{\mu}G$</TEX> heat interstellar gas to <TEX>$\~$</TEX>7 keV via magnetic reconnection (Tanuma et al. 1999). There will be the small-scale (< 10 pc) strong magnetic fields, which can be observed as <TEX>$(B)_{obs} \;\~3{\mu}G$</TEX> by integration of Faraday Rotation Measure, if it is localized by a volume filling factor of f <TEX>$\~$</TEX> 0.1. In order to examine this model, we solved three-dimensional (3D) resistive magnetohydrodynamic (MHD) equations numerically to examine the magnetic reconnect ion triggered by a supernova shock (fig.l). We assume that the magnetic field is Bx = 30tanh(y/20pc) <TEX>$\mu$</TEX>G, By = Bz = 0, and the temperature is uniform, at the initial condition. We put a supernova explosion outside the current sheet. The supernova-shock, as a result, triggers the magnetic reconnect ion, and the gas is heatd to > 7 keV. The magnetic reconnect ion heats the interstellar gas to <TEX>$\~$</TEX>7 keV in the Galactic plane, if it occurs in the locally strong magnetic fields of <TEX>$B_{local}\;\~30{\mu}G$</TEX>. The heated plasma is confined by the magnetic field for <TEX>$\~10^{5.5} yr$</TEX>. The required interval of the magnetic reconnect ions (triggered by anything) is <TEX>$\~$</TEX>1 - 10 yr. The magnetic reconnect ion will explain the origin of X-rays from the Galactic ridge, furthermore the Galactic halo, and clusters of galaxies.
713
- FUX ROGER
- Journal of the Korean astronomical society = 천문학회지
- 34, n.4
- pp.255-259
- 2001
- 원문 바로보기
PMDSPH is a combined 3D particle-mesh and SPH code aimed to simulate the self-consistent dynamical evolution of spiral galaxies including live stellar and collisionless dark matter components, as well as an isothermal gas component. This paper describes some aspects of this code and shows how its application to the Milky Way helps to recover the gas flow within the Galactic bar region from the observed HI and CO longitude-velocity distributions.
714
- 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.
715
- ALLEN ANTHONY
- Journal of the Korean astronomical society = 천문학회지
- 34, n.4
- pp.325-327
- 2001
- 원문 바로보기
This poster summarizes numerical collapse calculations of non-rotating and rotating singular, isothermal toroids that employed the zeus2d (Norman and Stone 1992) magnetohydrodynamics package. In the non-rotating collapse calculations, it is seen that infall proceeds at a constant rate and magnetically supported, high density pseudo-disks form in the equatorial plane. With rotating clouds, however, toroidal magnetic fields grow as infall proceeds, teaming with angular momentum to slow the inflow to the center and generate outflow.
716
- ANN H. B.
- Journal of the Korean astronomical society = 천문학회지
- 34, n.4
- pp.261-263
- 2001
- 원문 바로보기
Numerical simulations based on the smoothed particle hydrodynamics (SPH) is performed to investigate the dynamical properties of barred galaxies that have nuclear rings. The nuclear ring morphology depends on the relative strength of bar potentials. Nuclear rings form between the two ILRs and align perpendicular to the bars unless the bar potentials are strong enough to allow the x1 orbits near the ILRs. Shock dissipation plays a critical role in the formation of nuclear rings.
717
- 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.
718
- 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.
719
- KYEONG JAE-MANN
- Journal of the Korean astronomical society = 천문학회지
- 34, n.3
- pp.137-141
- 2001
- 원문 바로보기
We derive a new relationship between the giant branch slope as measured in the color-magnitude diagram (K, J - K) and [Fe/H] metallicity for old open clusters. Previously such relationships have been derived for globular clusters, while similar tendency has been expected for open clusters. New derived correlation, [Fe/H]=-17.2(<TEX>$\pm$</TEX>0.23)GB slope - 1.95(<TEX>$\pm$</TEX>0.02), is based on a collection of data for 10 old open clusters. Most clusters behave as expected from the theoretical predictions.
720
- 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.