모달창 닫기
- 홈으로 이동
1968년 ~ 2023년까지 1,187 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 : 1,187건 (DB Construction : 1,187 Articles)
총 게시글 1,187건
페이지 28/119
271
- Na, Sung-Ho
- Journal of the Korean astronomical society = 천문학회지
- 45, n.2
- pp.49-57
- 2012
- 원문 바로보기
In this study, I calculate the past and future dynamical states of the Earth-Moon system by using modified Lambeck's formulae. I find that the ocean tidal effect must have been smaller in the past compared to its present amount. Even though the Moon is already in the spin-orbit synchronous rotational state, my calculation suggest that it will not be in geostationary rotational state in the next billion years or so. This is due to the associated Earth's obliquity increase and slow retardation of Earth's spin and lunar orbital angular velocities. I also attempt to calculate the precessional period of the Earth in the future. To avoid uncertainties in the time scale, the future state is described by using the Earth-Moon distance ratio as independent parameter. Effects due to solar tidal dissipation are included in all calculations.
272
- Kim, Yong-Ha
- Journal of the Korean astronomical society = 천문학회지
- 45, n.2
- pp.39-48
- 2012
- 원문 바로보기
We investigate non-LTE effects on the <TEX>$H_3^+$</TEX> level populations to help the analysis of the observed 2 and 3.5 micron <TEX>$H_3^+$</TEX> emissions from the Jovian ionosphere. We begin by constructing a simple three-level model, in order to compute the intensity ratio of the R(3,4) line in the hot band to the Q(1,0) line in the fundamental band, which have been observed in the Jovian auroral regions. We find that non-LTE effects produce only small changes in the intensity ratios for ambient <TEX>$H_2$</TEX> densities less than or equal to <TEX>$5{\times}10^{11}cm^{-3}$</TEX>. We then construct two comprehensive models by including all the collisional and radiative transitions between pairs of more than a thousand known <TEX>$H_3^+$</TEX> rovibrational levels with energies less than 10000 <TEX>$cm^{-1}$</TEX>. By employing these models, we find that the intensity ratios of the lines in the hot and fundamental bands are affected greatly by non-LTE effects, but the details depend sensitively on the number of collisional and radiative transitions included in the models. Non-LTE effects on the rovibrational population become evident at about the same ambient <TEX>$H_2$</TEX> densities in the comprehensive models as in the three-level model. However, the models show that rotational temperatures derived from the intensities of rotational lines in the <TEX>${\nu}_2$</TEX> and <TEX>$2{\nu}_2$</TEX> bands may differ significantly from the ambie temperatures in the non-LTE regime. We find that significant non-LTE effects appear near and above the <TEX>$H_3^+$</TEX> peak, and that the kinetic temperatures in the Jovian thermospheric temperatures derived from the observed line ratios in the 2 and 3.5 micron <TEX>$H_3^+$</TEX> emissions are highly model dependent.
273
- Minh, Young Chol
- Journal of the Korean astronomical society = 천문학회지
- 45, n.6
- pp.157-166
- 2012
- 원문 바로보기
Using the Submillimeter Array (SMA), we identified two bright hot subcores, MM1a and MM1b (size ~ 1' and mass ~ 0.5 <TEX>$M_{\odot}$</TEX>) separated by about 1.600, in the 230 GHz continuum emission toward the massive star-forming region DR21(OH). Both display typical hot core characteristics but have slightly different chemical properties. For example, highly saturated species show stronger emission toward MM1a and seem to be evaporating directly from the grain mantles. In contrast, simple sulfur-bearing species have brighter emission at MM1b. These features indicate that MM1a is at an earlier stage than MM1b, and the small-scale chemical differences between these two cores may result from the age difference of the order of <TEX>$10^4$</TEX> years.
274
- Park, Myeong-Gu
- Journal of the Korean astronomical society = 천문학회지
- 45, n.4
- pp.101-110
- 2012
- 원문 바로보기
I present here one approach to general relativistic radiation hydrodynamics. It is based on covariant tensor conservation equations and considers only the frequency-integrated total energy and momentum exchange between matter and the radiation field. It is also a mixed-frame formalism in the sense that, the interaction between radiation and matter is described with quantities in the comoving frame in which the interaction is often symmetric in angle while the radiation energy and momentum equations are expressed in the fixed frame quantities in which the derivatives are simpler. Hence, this approach is intuitive enough to be applied straightforwardly to any spacetime or coordinate. A few examples are provided along with caveats in this formalism.
275
- Park, Hong-Soo
- Journal of the Korean astronomical society = 천문학회지
- 45, n.3
- pp.71-84
- 2012
- 원문 바로보기
We present a photometric study of the globular clusters (GCs) in the Virgo giant elliptical galaxy M86 based on Washington <TEX>$CT_1$</TEX> images. The colors of the GCs in M86 show a bimodal distribution with a blue peak at (<TEX>$C-T_1$</TEX>) = 1.30 and a red peak at (<TEX>$C-T_1$</TEX>) = 1.72. The spatial distribution of the red GCs is elongated similar to that of the stellar halo, while that of the blue GCs is roughly circular. The radial number density profile of the blue GCs is more extended than that of the red GCs. The radial number density profile of the red GCs is consistent with the surface brightness profile of the M86 stellar halo. The GC system has a negative radial color gradient, which is mainly due to the number ratio of the blue GCs to the red GCs increasing as galactocentric radius increases. The bright blue GCs in the outer region of M86 show a blue tilt: the brighter they are, the redder their mean colors get. These results are discussed in comparison with other Virgo giant elliptical galaxies.
276
- Lee, Ki-Won
- Journal of the Korean astronomical society = 천문학회지
- 45, n.4
- pp.85-91
- 2012
- 원문 바로보기
Astronomical data making such as forming a calendar, period of day, determining the time of rising/setting of the sun and the onset of twilight are essential in our daily lives. Knowing the calendar day of the past is particularly crucial for studying the history of a clan or a nation. To verify previous studies in the calendar day of the Joseon dynasty (1392 - 1910), we investigate the sexagenary cycle of the new moon day (i.e., the first day in a lunar month) by using sources such as results of the calculations using the Datong calendar (a Chinese Calendar of the Ming Dynasty) and the data of Baekjungryeok (a Perpetual Calendar; literally, a one hundred-year almanac). Compared with the study of Ahn et al., we find that as many as 17 sexagenary cycles show discrepancies. In the cases of nine discrepancies, we find that the sexagenary cycles of this study are identical to those of the almanacs at that time. In addition, we study five sexagenary cycles by using the historical accounts of Joseon Wangjo Sillok (Annals of the Joseon Dynasty), Seungjeongwon Ilgi (Daily Reports of Royal Secretariat), Chungung Ilgi (Logs of Crown Prince), and so forth. For the remaining discrepancies, we present historical literature supporting the results of this study. This study will greatly contribute to the identification of the lunisolar calendar days during the Joseon dynasty as the dates of the modern (i.e., Gregorian) calendar.
277
- 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.
278
- 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.
279
- 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.
280
- 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.