모달창 닫기
- 홈으로 이동
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 68/122
671
- AHN SANG-HYEON
- Journal of the Korean astronomical society = 천문학회지
- 35, n.4
- pp.175-185
- 2002
- 원문 바로보기
Almost half of primeval galaxies show P-Cygni type profiles in the Ly<TEX>$\alpha$</TEX> emission line. The main underlying mechanism for the profile formation in these systems is thought to be the frequency re-distribution of the line photons in expanding scattering media surrounding the emission source. A Monte Carlo code is developed to investigate the Ly<TEX>$\alpha$</TEX> line transfer in an optically thick and moving medium with a careful consideration of the scattering in the damping wings. Typical column densities and expansion velocities of neutral hydrogen investigated in this study are <TEX>$N_{H1}{\~}10^{17-20}\;cm^{-2}$</TEX> and <TEX>${\Delta}V{\~} 100 km\;s^{-1}$</TEX>. We investigate the dependence of the emergent profiles on the kinematics and on the column density. Our numerical results are applied to show that the damped Ly<TEX>$\alpha$</TEX> absorbers may possess an expanding H I supershell with bulk flow of <TEX>${\~}200 km\;s^{-l}$</TEX> and H I column density <TEX>$N_{H1}{\~}10^{19}\;cm^{-2}$</TEX>. We briefly discuss the observational implications.
672
- 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.
673
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.
674
- 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.
675
- HONG S. S.
- Journal of the Korean astronomical society = 천문학회지
- 35, n.1
- pp.41-57
- 2002
- 원문 바로보기
We have written a code called QDM_sca, which numerically solves the problem of radiative transfer in an anisotropically scattering, spherical atmosphere. First we formulate the problem as a second order differential equation of a quasi-diffusion type. We then apply a three-point finite differencing to the resulting differential equation and transform it to a tri-diagonal system of simultaneous linear equations. After boundary conditions are implemented in the tri-diagonal system, the QDM_sca radiative code fixes the field of specific intensity at every point in the atmosphere. As an application example, we used the code to calculate the brightness of atmospheric diffuse light(ADL) as a function of zenith distance, which plays a pivotal role in reducing the zodiacal light brightness from night sky observations. On the basis of this ADL calculation, frequent uses of effective extinction optical depth have been fully justified in correcting the atmospheric extinction for such extended sources as zodiacal light, integrated starlight and diffuse galactic light. The code will be available on request.
676
- CHAE JONGCHUL
- Journal of the Korean astronomical society = 천문학회지
- 35, n.1
- pp.59-65
- 2002
- 원문 바로보기
Solar observations support that magnetic reconnect ion ubiquitously occurs in the chromosphere as well as in the corona. It is now widely accepted that coronal magnetic reconnect ion is fast reconnect ion of the Petschek type, and is the main driver of solar flares. On the other hand, it has been thought that the traditional Sweet-Parker model may describe chromospheric reconnect ion without difficulty, since the electric conductivity in the chromoshphere is much lower than that in the corona. However, recent observations of cancelling magnetic features have suggested that chromospheric reconnect ion might proceed at a faster rate than the Sweet-Parker model predicts. We have applied the Sweet-Parker model and Petschek model to a well-observed cancelling magnetic feature. As a result, we found that the inflow speed of the Sweet-Parker reconnect ion is too small to explain the observed converging speed of the feature. On the other hand, the inflow speeds and outflow speeds of the Petschek reconnect ion are well compatible with observations. Moreover, we found that the Sweet-Parker type current sheet is subject to the ion-acoustic instability in the chromosphere, implying the Petschek mechanism may operate there. Our results strongly suggest that chromospheric reconnect ion is of the Petschek type.
677
- YANG YUJIN
- Journal of the Korean astronomical society = 천문학회지
- 35, n.3
- pp.131-141
- 2002
- 원문 바로보기
We present Near-IR photometry of the Arches cluster, a young and massive stellar cluster near the Galactic center. We have analyzed the high resolution (FWHM <TEX>$\~$</TEX> 0.2') Hand K' band images in the Galactic Center Demonstration Science Data Set, which were obtained with the Gemini/Hokupa's adaptive optics (AO) system. We present the color-magnitude diagram, the luminosity function and the initial mass function (IMF) of the stars in the Arches cluster in comparison with the HST/NICMOS data. The IMF slope for the range of 1.0 < log (M/M<TEX>$\bigodot$</TEX>) < 2.1 is estimated to be <TEX>${\Gamma} = -0.79 {\pm} 0.16$</TEX>, in good agreements with the earlier result based on the HST/NICMOS data [Figer et al. 1999, ApJ, 525, 750]. These results strengthen the evidence that the IMF of the bright. stars close to the Galactic center is much flatter than that for the solar neighborhood. This is also consistent with a recent finding that the IMFs of the bright stars in young clusters in M33 get flatter as the galactocentric distance decreases [Lee et al. 2001, astro-ph 0109258]. It is found that the power of the Gemini/ AO system is comparable, with some limits, to that of the HST/NICMOS.
678
- PARK CHAN-GYUNG
- Journal of the Korean astronomical society = 천문학회지
- 35, n.2
- pp.67-73
- 2002
- 원문 바로보기
We have made a topological study of cosmic microwave background (CMB) polarization maps by simulating the AMiBA experiment results. A ACDM CMB sky is adopted to make mock interferometric observations designed for the AMiBA experiment. CMB polarization fields are reconstructed from the AMiBA mock visibility data using the maximum entropy method. We have also considered effects of Galactic foregrounds on the CMB polarization fields. The genus statistic is calculated from the simulated Q and U polarization maps, where Q and U are Stokes parameters. Our study shows that the Galactic foreground emission, even at low Galactic latitude, is expected to have small effects on the CMB polarization field. Increasing survey area and integration time is essential to detect non-Gaussian signals of cosmological origin through genus measurement.
679
- CHOI CHUL-SUNG
- Journal of the Korean astronomical society = 천문학회지
- 35, n.1
- pp.1-7
- 2002
- 원문 바로보기
We have studied the long-term X-ray light curve (2-10 keV) of the luminous Seyfert 1 galaxy MCG-2-58-22 by compiling data, from various X-ray satellites, which together cover more than 20 years. We have found two distinct types of time variations in the light curve. One is a gradual and secular decrease of the X-ray flux, and the other is the episodic increase of X-ray flux (or flare) by a factor of 2-4 compared with the level expected from the secular variation. We detected 3 such flares in total; a representative duration for the flares is <TEX>$\~$</TEX>2 years, with intervening quiescent intervals lasting <TEX>$\~$</TEX>6-8 years. We discuss a few possible origins for these variabilities. Though a standard disk instability theory may explain the displayed time variability in the X-ray light curve, the subsequent accretions of stellar debris, from a tidal disruption event caused by a supermassive black hole in MCG-2-58-22, cannot be ruled out as an alternative explanation.
680
- OH SU YEON
- Journal of the Korean astronomical society = 천문학회지
- 35, n.3
- pp.151-157
- 2002
- 원문 바로보기
From the data of solar wind observation by ACE spacecraft orbiting the Earth-Sun Lagrangian point, we selected 48 forward interplanetary shocks(IPSs) occurred in 2000, maximum solar activity period. Examining the profiles of solar wind parameters, the IPSs are classified by their shock drivers. The significant shock drivers are the interplanetary coronal mass ejection(ICME) and the high speed stream(HSS). The IPSs driven by the ICMEs are classified into shocks driven by magnetic clouds and by ejectas based on the existence of magnetic flux rope structure and magnetic field strength. Some IPSs could be formed as the blast wave by the smaller energy and shorter duration of shock drivers such as type II radio burst. Out of selected 48 forward IPSs, <TEX>$56.2\%$</TEX> of the IPSs are driven by ICME, <TEX>$16.7\%$</TEX> by HSS, and <TEX>$16.7\%$</TEX> of the shocks are classified into blast-wave type shocks. However, the shock drivers of remaining <TEX>$10\%$</TEX> of the IPSs are unidentified. The classification of the IPSs by their driver is a first step toward investigating the critical magnitudes of the IPS drivers commencing the magnetic storms in each class.