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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 66/119
651
- 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.
652
- 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.
653
- 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.
654
- KIM SANG CHUL
- Journal of the Korean astronomical society = 천문학회지
- 35, n.1
- pp.9-28
- 2002
- 원문 바로보기
We present UBVI CCD photometry of the stellar contents and globular cluster(GC) candidates in the spiral galaxy NGC 300 in the Sculptor group. Color-magnitude diagrams for 18 OB associations having more than 30 member stars are presented. The slope of the initial mass function for the bright stars in NGC 300 is estimated to be <TEX>${\Gamma}= -2.6{\pm} 0.3$</TEX>. Assuming the distance to NGC 300 of (m - M)o = 26.53 <TEX>$\pm$</TEX> 0.07, the mean absolute magnitude of three brightest blue stars is obtained to be < <TEX>$M_v^{BSG}$</TEX> (3) > = -8.95 mag. We have performed search for GCs in NGC 300 and have found 17 GC candidates in this galaxy. Some characteristics of these GC candidates are discussed.
655
- 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.
656
- LEE CHANG WON
- Journal of the Korean astronomical society = 천문학회지
- 35, n.4
- pp.187-196
- 2002
- 원문 바로보기
A spectral line survey is performed from 159.7 to 164.7 GHz toward Orion-KL, as an extension of our previous line survey from 138.3 to 150.7 GHz with the same 14 m radio telescope of Taeduk Radio Astronomy Observatory. Typical system temperatures were 260 - 1000 K to achieve a sensitivity of about 0.02 - 0.04 K in TA unit. A total of 63 line spectra are detected in this survey. Among them, 54 lines lines are found to be the first detections towards an astronomical source and only 9 spectral lines have been previously identified from other observations. Forty-eight of 54 lines are believed to be from the known transitions of the known molecules, while 6 lines are 'unidentified'. All detected lines are found to be from a total of 10 molecular species and their isotopic variants. The molecular species with most numerous detected transitions are <TEX>$HCOOCH_3$</TEX> (22), followed by <TEX>$CH_3OCH_3$</TEX> (7), <TEX>$C_2H_5CN$</TEX> (7), and <TEX>$SO_2$</TEX> (6). The LTE rotation diagram analysis using all homogeneous data with those from previous survey gives more reliable determination of physical quantities. The derived values of the rotation temperatures and column densities for <TEX>$HCOOCH_3$</TEX>, <TEX>$CH_3OCH_3$</TEX>, and <TEX>$SO_2$</TEX> are are 75 <TEX>$\~$</TEX> 197 K and <TEX>$1.5 {\~}18 {\times} 10^{15}\;cm^{-2}$</TEX>, respectively.
657
- CHANG HEON-YOUNG
- Journal of the Korean astronomical society = 천문학회지
- 35, n.3
- pp.123-130
- 2002
- 원문 바로보기
An elliptical accretion disk may be formed by tidally disrupted debris of a flying-by star in an active galactic nucleus (AGN) or by tidal perturbation due to a companion in a binary black hole system. We investigate the iron K<TEX>$\alpha$</TEX> line profiles expecting from a geometrically thin, relativistic, elliptical disk in terms of model parameters, and find that a broad and skewed line profile can be reproduced well. Its shape is variable to the model parameters, such as, the emissivity power-law index, the ellipticity of the disk, and the major axis orientation of the elliptical accretion disk. We suggest that our results may be useful to search for such an elliptical disk and consequently the tidal disruption event.
658
- 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.
659
- 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.
660
- OKUDA TORU
- Journal of the Korean astronomical society = 천문학회지
- 34, n.4
- pp.251-254
- 2001
- 원문 바로보기
To examine the structure and dynamics of thick accretion disks, we use a two-dimensional viscous hydrodynamic code coupled with radiation transport. The <TEX>$\alpha$</TEX>-model and the full viscous stress-tensor description for the kinematic viscosity are used. The radiation transport is treated in the gray, flux-limited diffusion approximation. The finite difference methods used are based on an explicit-implicit method. We apply the numerical code to the Super-Eddington black-hole model for SS 433.@The result for a very small viscosity parameter a reproduces well the characteristic features of SS 433, such as the relativistic jets with <TEX>$\~$</TEX>0.26c, the small collimation degree of the jets, the mass-outflow rate of <TEX>${\ge}5{\times}10^{-7}M{\bigodot}yr^{-1}$</TEX>, and the formation of the X-ray iron emission lines.