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- 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 61/121
601
- DING M. D.
- Journal of the Korean astronomical society = 천문학회지
- 36, n.suppl1
- pp.49-54
- 2003
- 원문 바로보기
We introduce the two-dimensional spectral observations of solar flares using the Solar Tower Tele-scope of Nanjing University, China. In particular, we introduce three typical events and the methods used to analyze the data. (1) The flare of November 11, 1998, which is a limb flare. We derive the temperature and density within the flaring loop using non-LTE calculations. The results show that the loop top may be hotter and denser than other parts of the loop, which may be a result of magnetic reconnect ion above the loop. (2) The flare of March 10, 2001, which is a white-light flare that shows an emission enhancement at the near infrared continuum. We propose a model of non-thermal electron beam heating plus backwarming to interpret the observations. (3) The flare of September 29, 2002, which shows unusual line asymmetries at one flare kernel. The line asymmetries are caused by an upward moving plasma that is accelerated and heated during the flare development.
602
- ZHANG XIAOLEI
- Journal of the Korean astronomical society = 천문학회지
- 36, n.3
- pp.223-239
- 2003
- 원문 바로보기
It is now a well established fact that galaxies undergo significant morphological transformation during their lifetimes, manifesting as an evolution along the Hubble sequence from the late to the early Hubble types. The physical processes commonly believed to be responsible for this observed evolution trend, i.e. the major and minor mergers, as well as gas accretion under a barred potential, though demonstrated applicability to selected types of galaxies, on the whole have failed to reproduce the most important statistical and internal properties of galaxies. The secular evolution mechanism reviewed in this paper has the potential to overcome most of the known difficulties of the existing theories to provide a natural and coherent explanation of the properties of present day as well as high-redshift galaxies.
603
- KOO BON-CHUL
- Journal of the Korean astronomical society = 천문학회지
- 36, n.1
- pp.43-48
- 2003
- 원문 바로보기
We introduce and describe performance of the 6-meter telescope of Seoul Radio Astronomy Observatory (SRAO). All the softwares and instruments except the antenna structure and its driving system are developed for ourselves. The SIS mixer type receiver resulted in the receiver noise temperature less than 50 K (DSB) over the whole 3-mm radio window. An autocorrelation spectrometer, developed first in Korea, provides maximum 50 MHz band width over 1024 channels. Antenna surface is measured and adjusted using template method and radio holography which resulted in a superb surface accuracy bet-ter than 30<TEX>${\mu}m$</TEX>. Accordingly, the aperture and beam efficiences amount to <TEX>$70\%$</TEX> and <TEX>$75\%$</TEX>, respectively, largely independent of frequency in the 85 - 115 GHz range. It is also found that telescope pointing errors are less than 10' in both azimuth and elevation and that antenna gain is almost constant against elevation greater than <TEX>$20^{\circ}$</TEX>, without adjusting sub-reflector position. The SRAO 6-meter telescope is now fully operational and all these characteristics verify that observations are carried out with high precision and fidelity.
604
- KIM DONG-WOO
- Journal of the Korean astronomical society = 천문학회지
- 36, n.3
- pp.213-222
- 2003
- 원문 바로보기
We review recent observational results on early type galaxies obtained with high spatial resolution Chandra data. With its unprecedented high spatial resolution, Chandra reveals many intriguing features in early type galaxies which were not identified with the previous X-ray missions. In particular, various fine structures of the hot ISM in early type galaxies are detected, for example, X-ray cavities which are spatially coincident with radio jets/lobes, indicating the interaction between the hot ISM and radio jets. Also point sources (mostly LMXBs) are individually resolved down to Lx = a few x <TEX>$10^{37}\;erg\;sec^{-1}$</TEX> and it is for the first time possible to unequivocally investigate their properties and the X-ray luminosity function. After correcting for incompleteness, the XLF of LMXBs is well reproduced by a single power law with a slope of -1.0 - -1.5, which is in contrast to the previous report on the existence of the XLF break at Lx, Eddington = 2 x <TEX>$10^{38}\;erg\;sec^{-1}$</TEX> (i.e., Eddington luminosity of a neutron star binary). Carefully considering both detected and undetected, hidden populations of point sources we further discuss the XLF of LMXBs and the metal abundance of the hot ISM and their impact on the properties of early type galaxies.
605
- KANG HYESUNG
- Journal of the Korean astronomical society = 천문학회지
- 36, n.1
- pp.1-12
- 2003
- 원문 바로보기
Nonthermal particles can be produced due to incomplete thermalization at collisionless shocks and further accelerated to very high energies via diffusive shock acceleration. In a previous study we explored the cosmic ray (CR) acceleration at cosmic shocks through numerical simulations of CR modified, quasi-parallel shocks in 1D plane-parallel geometry with the physical parameters relevant for the shocks emerging in the large scale structure formation of the universe (Kang & Jones 2002). Specifically we considered pancake shocks driven by accretion flows with <TEX>$U_o = 1500 km\;s^{-l}$</TEX> and the preshock gas temperature of <TEX>$T_o = 10^4 - 10^8K$</TEX>. In order to consider the CR acceleration at shocks with a broader range of physical properties, in this contribution we present additional simulations with accretion flows with <TEX>$U_o = 75 - 1500 km\;s^{-l}$</TEX> and <TEX>$T_o = 10^4K$</TEX>. We also compare the new simulation results with those reported in the previous study. For a given Mach number, shocks with higher speeds accelerate CRs faster with a greater number of particles, since the acceleration time scale is <TEX>$t_{acc}\;{\propto}\;U_o^{-2}$</TEX>. However, two shocks with a same Mach number but with different shock speeds evolve qualitatively similarly when the results are presented in terms of diffusion length and time scales. Therefore, the time asymptotic value for the fraction of shock kinetic energy transferred to CRs is mainly controlled by shock Mach number rather than shock speed. Although the CR acceleration efficiency depends weakly on a well-constrained injection parameter, <TEX>$\epsilon$</TEX>, and on shock speed for low shock Mach numbers, the dependence disappears for high shock Mach numbers. We present the 'CR energy ratio', <TEX>${\phi}(M_s)$</TEX>, for a wide range of shock parameters and for <TEX>$\epsilon$</TEX> = 0.2 - 0.3 at terminal time of our simulations. We suggest that these values can be considered as time-asymptotic values for the CR acceleration efficiency, since the time-dependent evolution of CR modified shocks has become approximately self-similar before the terminal time.
606
- SHIN JUNHO
- Journal of the Korean astronomical society = 천문학회지
- 36, n.suppl1
- pp.117-124
- 2003
- 원문 바로보기
Pre-launch calibration data have been analyzed for evaluating the point spread function (PSF) of Yohkoh Soft X-ray Telescope (SXT). Especially, it is found crucial that the effect of undersampling should be treated properly. The best fit solution of the SXT PSF, which is modeled by an elliptical Moffat function, has been derived by the comparison with the ground experiment data. In order to examine the off-axis variation of the SXT PSF, we need to define in advance the location of the optical axis on the CCD. According to the previous studies, the off-axis variation of effective area (the vignetting function) may be approximated either by two non-concentric cones or by a cone with some flat distortions. There have been, however, no fully approved representations for the SXT vignetting effect. The effect of the shift of the optical axis from the geometrical center of the telescope is investigated by numerical simulation. It is revealed from our study that the full width at half maximum (FWHM) of the SXT PSF stays nearly constant within an error bound over the central area of the CCD where the solar disk is located.
607
- LEE JEONGWOO
- Journal of the Korean astronomical society = 천문학회지
- 36, n.suppl1
- pp.63-73
- 2003
- 원문 바로보기
Solar flares present a number of radiative characteristics indicative of kinetic processes of high energy particles. Proper understanding of the kinetic processes, however, relies on how well we can separate the acceleration from transport characteristics. In this paper, we discuss microwave and hard X-ray bursts as a powerful tool in investigating the acceleration and transport of high energy electrons. After a brief review of the studies devoted to the kinetic process of solar flare particles, we cast them into a simple formulation which allows us to handle the injection, trap, and precipitation of flare electrons self-consistently. The formulation is then taken as a basis for interpreting and analyzing a set of impulsive and gradual bursts occurred on 2001 April 6 observed with the Owens Valley Solar Array, and HXT/WBS onboard Yohkoh satellite. We quantify the acceleration, trap, and precipitation processes during each burst in terms of relevant time scales, and also determine ambient density and magnetic field. Our result suggests that it should be the acceleration property, in particular, electron pitch angle distribution, rather than the trap condition, that is mainly responsible for the distinctive properties of the impulsive and gradual flares.
608
- FANG C.
- Journal of the Korean astronomical society = 천문학회지
- 36, n.suppl1
- pp.55-61
- 2003
- 원문 바로보기
There are at least three effects of the non-thermal particle bombardment on the solar atmosphere: (1) non-thermal ionization and excitation; (2) proton-hydrogen charge exchange; (3) impact line polarization. Due to the non-thermal ionization and excitation effects of electron bombardments in flares, H<TEX>$\alpha$</TEX> line is widely broadened and shows a strong central reversal. Significant enhancements at the line wings of Ly<TEX>$\alpha$</TEX> and Ly<TEX>$\beta$</TEX> are also predicted. In the case of proton bombardment, less strong broadening and no large central reversal are expected. However, due to proton-hydrogen charge exchange, the enhancements at the red wings of Ly<TEX>$\alpha$</TEX> and especially of Ly<TEX>$\beta$</TEX> lines at the early impulsive phase of flares are significant. Electron beam can also in some cases generates visible and UV continuum emission in white-light flares. However, at the onset phase, a negative 'black' flare may appear in several seconds, due to the increase of the <TEX>$H^-$</TEX> opacity. The impact polarization of atomic lines can provide complementary information on the energetic particles, the energy transport and deposit in the solar chromosphere. New results of spectropolarimetric analysis for the major flare on July 23, 2002 are also given in the paper.
609
- POLAND A.I.
- Journal of the Korean astronomical society = 천문학회지
- 36, n.suppl1
- pp.151-154
- 2003
- 원문 바로보기
During the past decade the world solar physics community has made significant progress in understanding the Sun and its interaction with the heliosphere and Earth's magnetosphere. NASA in coordination and cooperation with many other countries has had impressive results with the SOHO, YOHKOH, POLAR, GEOTAIL, etc spacecraft. These successes have given us a sound foundation to proceed into the new century. The two current main efforts in the U.S. are the Solar Terrestrial Probes (STP) and Living With A Star (LWS) programs. The STP program is basically science driven with new missions being selected on the basis of basic science discovery. The LWS program is focused on understanding the basic physics of solar variability and its effects on Earth systems. The current plans for these two programs are discussed.
610
- Taniguchi, Yoshiaki
- Journal of the Korean astronomical society = 천문학회지
- 36, n.4
- pp.283-283
- 2003
- 원문 바로보기
The first sentence in the second paragraph of INTRODUCTION, 'The first discovery of a galaxy beyond z=5 was reported by Weymann et al. (1998); HDF 4-470.3 at z=5.60.' should be read as 'The first discovery of a galaxy beyond z=5 was reported by Dey et al. (1998); 0140+326 RD1 at z=5.34'. The authors sincerely regret this error.