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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
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681
A NEW CHANNEL TO SEARCH FOR EXTRA-SOLAR SYSTEMS WITH MULTIPLE PLANETS VIA GRAVITATIONAL MICROLENSING
- HAN CHEONGHO
- Journal of the Korean astronomical society = 천문학회지
- 35, n.1
- pp.35-40
- 2002
- 원문 바로보기
Gaudi, Naber & Sackett pointed out that if an event is caused by a lens system containing more than two planets, all planets will affect the central region of the magnification pattern, and thus the existence of the multiple planets can be inferred by detecting additionally deformed anomalies from intensive monitoring of high magnification microlensing events. Unfortunately, this method has important limitations in identifying the existence of multiple planets and determining their parameters (the mass ratio and the instantaneous projected separation) due to the degeneracy of the resulting light curve anomalies from those induced by a single planet and the complexity of multiple planet lensing models. In this paper, we propose a new channel to search for multiple planets via microlensing. The method is based on the fact that the lensing light curve anomalies induced by multiple planets are well approximated by the superposition of those of the single planet systems where the individual planet-primary pairs act as independent lens systems. Then, if the source trajectory passes both of the outer deviation regions induced by the individual planets, one can unambiguously identify the existence of the multiple planets. We illustrate that the probability of successively detecting light curve anomalies induced by two Jovian-mass planets located in the lensing zone through this channel will be substantial. Since the individual anomalies can be well described by much simpler single planet lensing models, the proposed method has an important advantage of allowing one to accurately determine the parameters of the individual planets.
682
- LEE SUNGHO
- Journal of the Korean astronomical society = 천문학회지
- 35, n.3
- pp.111-121
- 2002
- 원문 바로보기
We have measured the correlation functions of the optically selected clusters of galaxies in the Abell and the APM catalogs, and of the X-ray clusters in the X-ray-Brightest Abell-type Clusters of galaxies (XBACs) catalog and the Brightest Clusters Sample (BCS). The same analysis method and the same method of characterizing the resulting correlation functions are applied to all observational samples. We have found that the amplitude of the correlation function of the APM clusters is much higher than what has been previously claimed, in particular for richer subsamples. The correlation length of the APM clusters with the richness R <TEX>$\ge$</TEX> 70 (as defined by the APM team) is found to be <TEX>$r_0 = 25.4_{-3.0}^{+3.1}\;h^{-1}$</TEX> Mpc. The amplitude of correlation function is about 2.4 times higher than that of Croft et al. (1997). The correlation lengths of the Abell clusters with the richness class RC <TEX>$\ge$</TEX> 0 and 1 are measured to be <TEX>$r_0 = 17.4_{-1.1}^{+1.2}$</TEX> and <TEX>$21.0_{-2.8}^{+2.8}\;h^{-1}$</TEX> Mpc, respectively, which is consistent with our results for the APM sample at the similar level of richness. The richness dependence of cluster correlations is found to be <TEX>$r_0= 0.40d_c + 3.2$</TEX> where <TEX>$d_c$</TEX> is the mean intercluster separation. This is identical in slope with the Bahcall & West (1992)'s estimate, but is inconsistent with the weak dependence of Croft et al. (1997). The X-ray bright Abell clusters in the XBACs catalog and the X-ray selected clusters in the BCS catalog show strong clustering. The correlation length of the XBACs clusters with <TEX>$L_x {\ge}0.65{\times} 10^{44}\;h^{-2}erg\;s^{-1}$</TEX> is <TEX>$30.3_{-6.5}^{+8.2}\;h^{-1}$</TEX> Mpc, and that of the BCS clusters with <TEX>$L_x {\ge}0.70{\times} 10^{44}\;h^{-2}erg\;s^{-1}$</TEX> is <TEX>$30.2_{-8.9}^{+9.8}\;h^{-1}$</TEX> Mpc. The clustering strength of the X-ray clusters is much weaker than what is expected from the optical clusters.
683
- ANN HONG BAE
- Journal of the Korean astronomical society = 천문학회지
- 35, n.1
- pp.29-34
- 2002
- 원문 바로보기
We have conducted UBVI CCD photometry of an intermediate-age open cluster NGC 559 to investigate the effect of dynamical evolution on the stellar distributions in NGC 559. Our photometry allows better estimates of distance and age of the cluster owing to much deeper photometry (V <TEX>$\le$</TEX> 21) than previous ones. It is found that the luminosity function and mass function as well as the spatial stellar distributions are affected by the dynamical evolution. Mass segregation leads to the central concentration of the high mass stars, which results in the flattened mass function inside the half mass radius.
684
- LEE C.-W.
- Journal of the Korean astronomical society = 천문학회지
- 34, n.2
- pp.111-117
- 2001
- 원문 바로보기
Recently, we have set up a new digital CCD camera system, MicroMax YHS-1300 manufactured by Roper Scientific for Ha observation by Solar Flare Telescope at Bohyunsan Optical Astronomy Observatory. It has a 12 bit dynamic range, a pixel number of 1300<TEX>$\times$</TEX>1030, a thermoelectric cooler, and an electric shutter. Its readout speed is about 3 frames per second and the dark current is about 0.05 e-/p/s at <TEX>$-10^{\circ}C$</TEX>. We have made a system performance test by confirming the system linearity, system gain, and system noise that its specification requires. We have also developed a data acquisition software which connects a digital camera con-troller to a PC and acquires H<TEX>$\alpha$</TEX> images via Microsoft Visual C++ 6.0 under Windows 98. Comparisons of high quality H<TEX>$\alpha$</TEX> images of AR 9169 and AR 9283 obtained from SOFT with the corresponding images from Learmonth Solar Observatory in Australia confirm that our H<TEX>$\alpha$</TEX> digital observational system is performed properly. Finally, we present a set of H<TEX>$\alpha$</TEX> images taken from a two ribbon flare occurred in AR 9283.
685
- 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.
686
- LEE YOUNGUNG
- Journal of the Korean astronomical society = 천문학회지
- 34, n.1
- pp.1-8
- 2001
- 원문 바로보기
We present a fast reduction method of survey data obtained using a single-dish radio telescope. Along with a brief review of classical method, a new method of identification and elimination of negative and positive bad channels are introduced using cloud identification code and several IRAF (Image Reduction and Analysis Facility) tasks relating statistics. Removing of several ripple patterns using Fourier Transform is also discussed. It is found that BACKGROUND task within IRAF is very efficient for fitting and subtraction of base-line with varying functions. Cloud identification method along with the possibility of its application for analysis of cloud structure is described, and future data reduction method is discussed.
687
- 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.
688
- MONAGHAN J. J.
- Journal of the Korean astronomical society = 천문학회지
- 34, n.4
- pp.203-207
- 2001
- 원문 바로보기
SPH is the shorthand for Smoothed Particle Hydrodynamics. This method is a Lagrangian method which means that it involves following the motion of elements of fluid. These elements have the characteristics of particles and the method is called a particle method. A useful review of SPH (Monaghan 1992) gives the basic technique and how it can be applied to numerous problems relevant to astrophysics. You can get some basic SPH programs from http) /www.maths.monash.edu.au/jjm/sphlect In the present lecture I will assume that the student has studied this review and therefore understands the basic principles. In today's lecture I plan to approach the equations from a different perspective by using a variational principle.
689
- SOHN YOUNG-JONG
- Journal of the Korean astronomical society = 천문학회지
- 34, n.2
- pp.59-66
- 2001
- 원문 바로보기
In this paper, we investigate the correlation between the radial ultraviolet color distribution and the shapes of the ultraviolet isophote for elliptical galaxies (M32, NGC 1399) and spiral bulges (of M31, M81) by using their archival UIT images. For M31, M81, and NGC 1399, the radial ultraviolet color distributions show a two-component trend; as the distance from the galactic center increase the color becomes redder in the inner region while it becomes bluer in the outer region. On the other hand, the color of M32 continues to become bluer with the increasing galactocentric distance. We also find, unlike the optical/IR images, significant variations of the position angle and the ellipticity in the ultraviolet isophotes of M31, M81, and NGC 1399 through the inner regions. For M32, the variation is significant in the outer region. Since these variation implies the triaxiality of their intrinsic shapes, we suggest that the early-type galaxies and spiral bulges with a radial color gradient in ultraviolet tend to have a triaxiality. On the other hand, the shape parameter characterized by the fourth order cosine Fourier coefficient of the isophote, a(4)/a, indicates that the systematic deviations of the ultraviolet isophotes of the four galaxies are smaller than <TEX>$\~0.2\%$</TEX> in units of the semi-major axis. The latter result implies that the ultraviolet isophotes of the galaxies have a pure elliptical shape rather than the boxy or disky shapes. Therefore, there is no clear evidence of correlation between the radial ultra-violet color gradient and the boxy/disky shapes of isophotes.
690
- RYU DONGSU
- Journal of the Korean astronomical society = 천문학회지
- 34, n.4
- pp.209-213
- 2001
- 원문 바로보기
This paper describes the numerical solution to the hyperbolic system of magnetohydrodynamic (MHD) equations. First, by pointing out the approximations involved, the deal MHD equations are presented. Next, the MHD waves as well as the associated shocks and discontinuities, are presented. Then, based on the hyperbolicity of the ideal MHD equations, the application of upwind schemes, which have been developed for hydrodynamics, is discussed to solve the equations numerically. As an definite example, one and multi-dimensional codes based on the Total Variation Diminishing scheme are presented. The treatment in the multi-dimensional code, which maintains <TEX>${\nabla}{\cdot}$</TEX>B = 0, is described. Through tests, the robustness of the upwind schemes for MHDs is demonstrated.