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- 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 31/122
301
- Kang, Hyesung
- Journal of the Korean astronomical society = 천문학회지
- 45, n.5
- pp.127-138
- 2012
- 원문 바로보기
We explore how wave-particle interactions affect diffusive shock acceleration (DSA) at astrophysical shocks by performing time-dependent kinetic simulations, in which phenomenological models for magnetic field amplification (MFA), Alfv<TEX>$\acute{e}$</TEX>nic drift, thermal leakage injection, Bohm-like diffusion, and a free escape boundary are implemented. If the injection fraction of cosmic-ray (CR) particles is <TEX>${\xi}$</TEX> > <TEX>$2{\times}10^{-4}$</TEX>, for the shock parameters relevant for young supernova remnants, DSA is efficient enough to develop a significant shock precursor due to CR feedback, and magnetic field can be amplified up to a factor of 20 via CR streaming instability in the upstream region. If scattering centers drift with Alfv<TEX>$\acute{e}$</TEX>n speed in the amplified magnetic field, the CR energy spectrum can be steepened significantly and the acceleration efficiency is reduced. Nonlinear DSA with self-consistent MFA and Alfv<TEX>$\acute{e}$</TEX>nic drift predicts that the postshock CR pressure saturates roughly at ~10 % of the shock ram pressure for strong shocks with a sonic Mach number ranging <TEX>$20{\leq}M_s{\leq}100$</TEX>. Since the amplified magnetic field follows the flow modification in the precursor, the low energy end of the particle spectrum is softened much more than the high energy end. As a result, the concave curvature in the energy spectra does not disappear entirely even with the help of Alfv<TEX>$\acute{e}$</TEX>nic drift. For shocks with a moderate Alfv<TEX>$\acute{e}$</TEX>n Mach number (<TEX>$M_A$</TEX> < 10), the accelerated CR spectrum can become as steep as <TEX>$E^{-2.1}$</TEX> - <TEX>$E^{-2.3}$</TEX>, which is more consistent with the observed CR spectrum and gamma-ray photon spectrum of several young supernova remnants.
302
- Lee, Jung-Won
- Journal of the Korean astronomical society = 천문학회지
- 45, n.5
- pp.117-125
- 2012
- 원문 바로보기
We present <TEX>$^{12}CO$</TEX> J = 2-1 line observations of G54.1+0.3, a composite supernova remnant with a mid-infrared (MIR) loop surrounding the central pulsar wind nebula (PWN). We map an area of <TEX>$12^{\prime}{\times}9^{\prime}$</TEX> around the PWN and its associated MIR loop. We confirm two velocity components that have been proposed to be possibly interacting with the PWN/MIR-loop; the +53 km <TEX>$s^{-1}$</TEX> cloud, which appears in contact with the eastern boundary of the PWN and the +23 km <TEX>$s^{-1}$</TEX> cloud, which has CO emission coincident with the MIR loop. However, we have not found a direct evidence for the interaction in either of these clouds. Instead, we detected an 5'-long arc-like cloud at +15-+23 km <TEX>$s^{-1}$</TEX> with a systematic velocity gradient of ~3 km <TEX>$s^{-1}$</TEX> <TEX>$arcmin^{-1}$</TEX> and broad-line emitting CO gas with widths (FWHM) of <TEX>${\leq}7km\;s^{-1}$</TEX> in the western interior of the supernova remnant. We discuss their association with the supernova remnant.
303
- Li, Xue-Bao
- Journal of the Korean astronomical society = 천문학회지
- 45, n.1
- pp.19-24
- 2012
- 원문 바로보기
Microthermal fluctuations are introduced by atmospheric turbulence very near the ground. In order to detect microthermal fluctuations at Fuxian Solar Observatory (FSO), a microthermal instrument has been developed. The microthermal instrument consists of a microthermal sensor, which is based on a Wheatstone bridge circuit and uses fine tungsten filaments as resistance temperature detectors, an associated signal processing unit, and a data collection, & communication subsystem. In this paper, after a brief introduction to surface layer seeing, we discuss the instrumentation behind the microthermal detector we have developed and then present the results obtained. The results of the evaluation indicate that the effect of the turbulent surface boundary layer to astronomical seeing would become sufficiently small when installing a telescope at a height of 16m or higher from the ground at FSO.
304
- Youn, So-Young
- Journal of the Korean astronomical society = 천문학회지
- 45, n.4
- pp.93-99
- 2012
- 원문 바로보기
We present a 1.1mm emission map of the OMC1 region observed with AzTEC, a new large-format array composed of 144 silicon-nitride micromesh bolometers, that was in use at the James Clerk Maxwell Telescope (JCMT). These AzTEC observations reveal dozens of cloud cores and a tail of filaments in a manner that is almost identical to the submillimeter continuum emission of the entire OMC1 region at 450 and <TEX>$850{\mu}m$</TEX>. We perform Fourier analysis of the image with a modified periodogram and the density power spectrum, which provides the distribution of the length scale of the structures, is determined. The expected value of the periodogram converges to the resulting power spectrum in the mean squared sense. The present analysis reveals that the power spectrum steepens at relatively smaller scales. At larger scales, the spectrum flattens and the power law becomes shallower. The power spectra of the 1.1mm emission show clear deviations from a single power law. We find that at least three components of power law might be fitted to the calculated power spectrum of the 1.1mm emission. The slope of the best fit power law, <TEX>${\gamma}{\approx}-2.7$</TEX> is similar to those values found in numerical simulations. The effect of beam size and the noise spectrum on the shape and slope of the power spectrum are also included in the present analysis. The slope of the power law changes significantly at higher spatial frequency as the beam size increases.
305
- Deng, Xin-Fa
- Journal of the Korean astronomical society = 천문학회지
- 45, n.3
- pp.59-64
- 2012
- 원문 바로보기
Using the volume-limited Main galaxy sample constructed from the Sloan Digital Sky Survey Data Release 7 (SDSS DR7), we explore the environmental dependence of the fraction of 'unconventional' galaxies: luminous blue and faint red. It is found that the fraction of faint red increases apparently with increasing local density, and the fraction of luminous blue declines substantially with increasing local density, which shows that there is an environmental dependence for color beyond that for luminosity.
306
- Lee, Sung Hwan
- Journal of the Korean astronomical society = 천문학회지
- 45, n.5
- pp.111-116
- 2012
- 원문 바로보기
We present a mathematical model that predicts the variation of illuminance during a solar eclipse, considering continuous effects of limb darkening. We assume that (1) the Sun and the Moon constitute perfect spheres, (2) the Moon crosses the Sun with a constant apparent velocity, and (3) sunspots, prominences, and coronae can be neglected. We compare predictions of this model with actual measurements made by M<TEX>$\ddot{o}$</TEX>llmann & Vollmer (2006) during a total solar eclipse in Turkey, and with predictions of existing models. The new model is shown to describe the actual phenomenon more accurately than existing models.
307
- Kim, Chul-Hee
- Journal of the Korean astronomical society = 천문학회지
- 45, n.2
- pp.25-29
- 2012
- 원문 바로보기
New methods are developed to estimate the effective temperature (Te), surface gravity (log g), and metallicity ([A/H]) simultaneously with the spectral line depth ratios. Using the model atmosphere grids, depth values are calculated for the wavelength range of <TEX>$4000{\AA}-5600{\AA}$</TEX> for various temperatures, gravities, and metallicities. All possible different combinations of line depth ratios for different pairs of ratios are investigated. A graphical 3D figure is produced with X, Y, and Z axes corresponding to Te, log g, and [A/H], respectively. By reading a cross point of two curves plotted by a connection of three parameters obtained from spectral line depth ratio pairs on each of the three projected planes, Te, log g, and [A/H] are determined simultaneously. In addition, an analytical method is devised based on the similar algorithm developed for the graphical method. Our methods were applied to estimate the fundamental atmospheric parameters of the Sun and Arcturus.
308
- Suh, Kyung-Won
- Journal of the Korean astronomical society = 천문학회지
- 44, n.1
- pp.13-21
- 2011
- 원문 바로보기
We model dust around Herbig Ae/Be stars using a radiative transfer model for multiple isothermal circumstellar dust shells to reproduce the multiple broad peaks in their spectral energy distributions (SEDs). Using the opacity functions for various types of dust grains at different temperatures, we calculate the radiative transfer model SEDs for multiple dust shells. For eight sample stars, we compare the model results with the observed SEDs including the Infrared Space Observatory (ISO) and AKARI data. We present model parameters for the best fit model SEDs that would be helpful to understand the overall structure of dust envelopes around Herbig Ae/Be stars. We find that at least four separate dust components are required to reproduce the observed SEDs. For all the sample stars, two innermost dust components (a hot component of 1000-1500 K and a warm component of 300-600 K) with amorphous silicate and carbon grains are needed. Crystalline dust grains (corundum, forsterite, olivine, and water ice) are needed for some objects. Some crystalline dust grains exist in cold regions as well as in hot inner shells.
309
- Deng, Lin-Hua
- Journal of the Korean astronomical society = 천문학회지
- 44, n.6
- pp.209-215
- 2011
- 원문 바로보기
In this paper, the long-term hemispheric variation of the polar faculae is investigated. It is found that, (1) both the N-S asymmetry and N-S asynchrony of the polar faculae exhibit a long-term persistence, which suggests that they should not be regarded as a stochastic phenomenon; (2) both the N-S asynchrony and N-S asymmetry of the polar faculae are functions of the latitude, implying that the N-S asynchrony of the polar faculae is related to the N-S asymmetry of the polar faculae; (3) from a long-term view, the dominant hemisphere of the polar faculae seems to have close connection with the phase-leading hemisphere of the polar faculae.
310
- Le, Huynh Anh Nguyena
- Journal of the Korean astronomical society = 천문학회지
- 44, n.4
- pp.125-134
- 2011
- 원문 바로보기
We present medium resolution (R = 5000 - 6000) spectra in the near-infrared band, 1.4 - 1.8 <TEX>${\mu}m$</TEX>, for template stars in G, K, and M types observed by the echelle spectrometer, IRCS, at the SUBARU 8.2 m telescope. The identification of lines is based on the spectra of Arcturus (K2 III) in the literature. We measured the equivalent of widths and compared our results to those of Meyer et al. (1998). We conclude that our spectral resolution (R = 6000) data can investigate more accurately the properties of lines in stellar spectra. The library of the template stellar spectra in ASCII format are available for download on the World Wide Web.